Just a snapshot of the amazing fauna that can be found in "our backyard". There was a playful group of these tiny monkeys at the hotel's garden one afternoon. Awesome!
Friday, August 13, 2010
Wonders of Joao Pessoa
Just a snapshot of the amazing fauna that can be found in "our backyard". There was a playful group of these tiny monkeys at the hotel's garden one afternoon. Awesome!
Halo nuclei
Last afternoon we heard about neutron halos in C nuclei, by Tobias Frederico. I was looking forward to this talk, as one of the projects I have lined up for my postdoc work is measuring radii of weakly bound light neutron rich nuclei (maybe even carbon; should read the proposal again!). The outline was there; the talks would start with explanations of the Thomas Collapse and some Efimov Effect that would somewhat pop up again later. I understood Thomas was working on physics around 1935, but what collapsed then was my interest in the talk! The speaker explained why the Thomas collapse happens, but failed to define or explain what the collapse of a quantum mechanical system is. I think he assumed it was something advanced undergrads would be very familiar with, but it's been too long since I'm one of those creatures.
However, after a few more slides I somewhat caught up with it and constructed a picture in my imagination that looked like this: Frederico constructed a simple model of a core + 2 neutrons using some energies of the system as 'scale parameters' (such thing is coming from Efimov). The parameters are just the binding energy between the two neutrons, or a neutron and the core, or the total binding energy of the system (the 4th one sounded just like being also the binding energy to me). Playing with these you can predict what type of halo nuclei you'll have, which are classified by the Latinamerican music they prefer to dance... tango, zamba (a tongue in cheek nomenclature for the possibility of having bound states between two of the three subsystems of the halo nuclei). With that models he obtained what accounts for a parameterization of the matter radius of the system on the binding energy, so he was quite excited with some of the first results from RIKEN on interaction cross sections. An attempt to compare his predicted binding energy with the known mass of 20C (or was it 19C) didn't go so well, but there were large error bars all over the place: in the end these are ultra neutron rich isotopes we're dealing with!
In conclusion, he'd love to see an experiment in 19C + n scattering and test his theory. We'd all love to see it, a 19C or a neutron target would be pretty cool things ... What about using this indirect 19C(d,p)20C things??
However, after a few more slides I somewhat caught up with it and constructed a picture in my imagination that looked like this: Frederico constructed a simple model of a core + 2 neutrons using some energies of the system as 'scale parameters' (such thing is coming from Efimov). The parameters are just the binding energy between the two neutrons, or a neutron and the core, or the total binding energy of the system (the 4th one sounded just like being also the binding energy to me). Playing with these you can predict what type of halo nuclei you'll have, which are classified by the Latinamerican music they prefer to dance... tango, zamba (a tongue in cheek nomenclature for the possibility of having bound states between two of the three subsystems of the halo nuclei). With that models he obtained what accounts for a parameterization of the matter radius of the system on the binding energy, so he was quite excited with some of the first results from RIKEN on interaction cross sections. An attempt to compare his predicted binding energy with the known mass of 20C (or was it 19C) didn't go so well, but there were large error bars all over the place: in the end these are ultra neutron rich isotopes we're dealing with!
In conclusion, he'd love to see an experiment in 19C + n scattering and test his theory. We'd all love to see it, a 19C or a neutron target would be pretty cool things ... What about using this indirect 19C(d,p)20C things??
Thursday, August 12, 2010
Fusion with rare isotope beams
The talk given by prof. Ernst Rhem was really nice. He is very kind and a good person to work. I'm his fan . : )
Ernst talked about the advantages and problems to use radioactive beams to perform fusion reactions. In his seminar, he aborded some techniques to produce radioactive beams and gave an overview for the future using rare isotope beams.
Ernst talked about the advantages and problems to use radioactive beams to perform fusion reactions. In his seminar, he aborded some techniques to produce radioactive beams and gave an overview for the future using rare isotope beams.
Identification of isomers- A tricky business
Ana Bacerril just gave an informative talk on the latest experimental program at NSCL-MSU aimed at pinning down the structure of isotopes in the 100Sn region. She gave a didactic introduction on nuclear isomerism and I finally understood the three mechanisms underlying this phenomenon (shape, spin-gap and K-isomers). The main highlights were the measurements of the half life of the beta decay of 96Cd, hints on isomer of 98In and new gamma lines for 96Ag. The latter result was compared against shell model calculations performed by B. A. Brown.
Breit Idea
Title: Breit Equation in Nuclear Physics
Victim: Marek Nowakowski
Here comes the experimentalist-on-theorist tough love.
16.03 Marek plans on being paced appropriately, but we’ll see, eh?
16.06 3 eqn. on second slide, including GR notation. Nope. Didn’t make it.
16.07 Shit 6-7 eqn. Ok, buckle in, kiddies. Rough ride ahead. Reaching for Excedrin.
16.08 "Bump-tail" parameter. Mind is wandering. And he hates experimentalists, clearly. What did we do to him? I'm searching my memory....
16.10 An eqn with 24 terms filling the slide. Are you serious? If you didn’t want me to pay attention, just write talk in red on blue or yellow on white, and I’ll get the picture. No need to be passive aggressive about it.
16.11 H atom: consider final size of proton (“one of the smallest known corrections”) To that big equation? Corrections to energy, apparently.
16.14 dE ~2.396E-9 eV for binding energy. Why do we care then??? So small!!
16.14 Confirms my assessment- sooooooo small. HOWEVER, QED corrections to recoil on order of E-9. Readiative recoil correction is E-11. Three loops E-15. Holy cow.
16.15 Hyperfine splitting 1S hyperfine frequency—precise enough to see correction due to finite size of proton… quoted as -37.7 kHz
16.16 Hardonic atoms”capture of ...” whoah- slide is gone. Will have to catch it on the wiki.
16.18 Electromagnetic binding of atoms corrections from strong int (shifts energy levels). Look- if you say "atoms" you imply that you are talking about the electrons, not the nucleons.
16.25 In summary, talked about nuclear finite-size effects arising due to electromagnetic form factors.
Ernesto asks about that article that was recently published in which the size of the proton was measured 4% off from expectations—Marek says they need a correction term. There is no time to clarify whether this is a matter of interpretting their data to extract the radius or if there was an issue elsewhere.
Victim: Marek Nowakowski
Here comes the experimentalist-on-theorist tough love.
16.03 Marek plans on being paced appropriately, but we’ll see, eh?
16.06 3 eqn. on second slide, including GR notation. Nope. Didn’t make it.
16.07 Shit 6-7 eqn. Ok, buckle in, kiddies. Rough ride ahead. Reaching for Excedrin.
16.08 "Bump-tail" parameter. Mind is wandering. And he hates experimentalists, clearly. What did we do to him? I'm searching my memory....
16.10 An eqn with 24 terms filling the slide. Are you serious? If you didn’t want me to pay attention, just write talk in red on blue or yellow on white, and I’ll get the picture. No need to be passive aggressive about it.
16.11 H atom: consider final size of proton (“one of the smallest known corrections”) To that big equation? Corrections to energy, apparently.
16.14 dE ~2.396E-9 eV for binding energy. Why do we care then??? So small!!
16.14 Confirms my assessment- sooooooo small. HOWEVER, QED corrections to recoil on order of E-9. Readiative recoil correction is E-11. Three loops E-15. Holy cow.
16.15 Hyperfine splitting 1S hyperfine frequency—precise enough to see correction due to finite size of proton… quoted as -37.7 kHz
16.16 Hardonic atoms”capture of ...” whoah- slide is gone. Will have to catch it on the wiki.
16.18 Electromagnetic binding of atoms corrections from strong int (shifts energy levels). Look- if you say "atoms" you imply that you are talking about the electrons, not the nucleons.
16.25 In summary, talked about nuclear finite-size effects arising due to electromagnetic form factors.
Ernesto asks about that article that was recently published in which the size of the proton was measured 4% off from expectations—Marek says they need a correction term. There is no time to clarify whether this is a matter of interpretting their data to extract the radius or if there was an issue elsewhere.
Good Will Newton
Any relation, Will? To Newton?
Title: Towards a Better Understanding of Nuclear Matter: Synthesizing Neutron Star Observations and Nuclear Experiment
10.00 Choco- bacon. Seems to be for shock effect. Didn’t have breakfast this morning, so it has a slightly different effect on your blogger.
10.01 Blaming Google for his representation of nuclear physicists. Crowd appreciates the friendly start to the talk. A little chit chat is nice before… you know. Take note, kids.
10.02 Arrows everywhere. Interdependence between subfields. We get it. It takes a village.
10.02 J0737-3039 Double pulsar, A & B. Looks like my flight number. 22.7 ms and 2.77 s rotational periods for the two pulsars, respectively. Opposites attract, I guess.
10.03 Did someone say--- muuuurder?? My idea of using crime as a metaphor for nuclear physics is being carried to fruition here. I was thinking more along the lines of a mafia syndicate ande cooked books to describe the discrepencies between the Hamiltonians we construct and what Nature uses.
10.06 e-capture is Will's fall guy for pulsar B formation, and crime of double homicide. There is no statute of limitations here. He is going to lay out the case and take it to the jury. Who killed Pulsar B??
10.10 Wrapping up SNe feature list.
10.13 Distinguishing the rest mass and measured mass of pulsar, which is going to include gravitational binding energy of star. EOS is relevant. M_0/R is relevant here.
10.15 Aw- I really don’t feel like listening to EOS crap. Shouldn’t do that to people before noon, Will. Ya- I’m talking to you, man. EOS slides are ALWAYS boring. It is the only thing worse than spectroscopic factors.
10.16 Isospin asymmetries are “alpha.” Should be nice and confusing.
10.18 Symmetry energy discussed, with list of recent studies.
10.21 Zero minutes left warning is interpreted by Will as ~ 5 minutes left. Common approximation for theorists and crazies. (He's a theorist.) Will made the mistake of assuming the session chair was giving other warnings, too. Ahem.
10.24 Constraints are zeroing in on symmetry energy and mass….
10.26 “…final note,….”
10.27 Questions: tolerance for fallback? Simulations of the SNe explosion give E-3 M_solar if any at all. Will recommends seasoning his slides with salt. You should take most of what he says with a grain of salt: he's Brittish. Hendrik: wouldn’t we expect this to happen more frequently given how common e-capture SNe are? Zach: difference in frequencies for A and B…? Spin up of one from L transfer from the other. (Zach is a shoo-in for the student with the most zeal for asking questions. It is a cry for help- just not the kind you think.)
Title: Towards a Better Understanding of Nuclear Matter: Synthesizing Neutron Star Observations and Nuclear Experiment
10.00 Choco- bacon. Seems to be for shock effect. Didn’t have breakfast this morning, so it has a slightly different effect on your blogger.
10.01 Blaming Google for his representation of nuclear physicists. Crowd appreciates the friendly start to the talk. A little chit chat is nice before… you know. Take note, kids.
10.02 Arrows everywhere. Interdependence between subfields. We get it. It takes a village.
10.02 J0737-3039 Double pulsar, A & B. Looks like my flight number. 22.7 ms and 2.77 s rotational periods for the two pulsars, respectively. Opposites attract, I guess.
10.03 Did someone say--- muuuurder?? My idea of using crime as a metaphor for nuclear physics is being carried to fruition here. I was thinking more along the lines of a mafia syndicate ande cooked books to describe the discrepencies between the Hamiltonians we construct and what Nature uses.
10.06 e-capture is Will's fall guy for pulsar B formation, and crime of double homicide. There is no statute of limitations here. He is going to lay out the case and take it to the jury. Who killed Pulsar B??
10.10 Wrapping up SNe feature list.
10.13 Distinguishing the rest mass and measured mass of pulsar, which is going to include gravitational binding energy of star. EOS is relevant. M_0/R is relevant here.
10.15 Aw- I really don’t feel like listening to EOS crap. Shouldn’t do that to people before noon, Will. Ya- I’m talking to you, man. EOS slides are ALWAYS boring. It is the only thing worse than spectroscopic factors.
10.16 Isospin asymmetries are “alpha.” Should be nice and confusing.
10.18 Symmetry energy discussed, with list of recent studies.
10.21 Zero minutes left warning is interpreted by Will as ~ 5 minutes left. Common approximation for theorists and crazies. (He's a theorist.) Will made the mistake of assuming the session chair was giving other warnings, too. Ahem.
10.24 Constraints are zeroing in on symmetry energy and mass….
10.26 “…final note,….”
10.27 Questions: tolerance for fallback? Simulations of the SNe explosion give E-3 M_solar if any at all. Will recommends seasoning his slides with salt. You should take most of what he says with a grain of salt: he's Brittish. Hendrik: wouldn’t we expect this to happen more frequently given how common e-capture SNe are? Zach: difference in frequencies for A and B…? Spin up of one from L transfer from the other. (Zach is a shoo-in for the student with the most zeal for asking questions. It is a cry for help- just not the kind you think.)
Dark Blog
First up today, the final Thursday of the conference, is Pedro Alevino with "Dark matter and dark energy: a review and prospects"
9.05 He is not a nuclear physicist - he's a cosmologist.
9.11 Hubble expansion implies an age of the universe of 14Gyr. Completely wrong of course - Genesis tells us it's only around 6,000 yrs old. I've seen the dinosaur footprints next to the human footprints.
9.13 Need an accelerating universe to give an age of universe greater than 10Gyr. This is puzzling to me - from my cosmology course I distinctly remembering solving the Friedmann-Robertson-Walker equations and getting a universe age of 13Gyr without any dark energy. Hmmmm...
9.14 And now the FRW equations and EoS of the universe are flashed up. We're introduced to omegas:
Omega_m - density of matter/critical density of matter
Omega_e - density of dark energy/critical density of matter
9.16 Critical density: smaller - expand forever, greater - collapses at some point. This is without dark energy.
9.17 Dark energy has already been assumed to exist. Evidence to follow...
9.20 Primordial nucleosynthesis, when T < 0.1MeV. From nucleosynthesis, we can derive that 5% of matter density of universe is baryonic.
9.24 Cosmic Microwave Background is shown. Most perfect black body spectrum known. Not totally perfect though, there are observed temperature fluctuations due to density fluctuations in the plasma of the early universe.
9.25 Size of fluctuations consistent with flat universe.
9.26 These fluctuations are responsible for large scale structure formation - we can see their echo in the distribution of galaxies.
9.27 I get the feeling that the speaker is going for a shock and awe approach to the talk. Cosmologists do simulations with more particles than there are people on Earth!
9.29 Here comes the Type Ia SN evidence. He skips over the fact that the data appears consistent with no dark energy as well as dark energy.
9.31 Dark matter! Evidence: rotation curves of galaxies. He mentions changing gravity, but this doesn't work in explaining galaxy cluster collisions (e.g. the Bullet cluster). I have been to talks by Modified Gravity people claiming that it can.
9.36 The next slide loses me, partly because I missed the definition of the 'w' parameter which tells us about the dark energy EoS. 9.37 More long equations. Shock and awe.
9.38 Not natural to have w = constant, apparently. Indeed, it's illegal in 13 states in the US.
9.39 What the ?&$%? I wouldn't want to look at that slide on hallucenogenics. I'm stuggling with just coffee.
9.40 I have absolutely no idea what these domain wall networks are. But they can provide dark energy.
9.41 Relativistic and non-relativistic colored splotches are shown. They both look the same. Nevertheless one is ruled out.
9.42 Unified dark matter and dark energy! What are we going to call this unholy union?
9.45 The Planck satellite is going to constrain some of this stuff by measuring the CMB to unprecedented accuracy.
9.46 Summary: everything is known, except for what is dark matter and dark energy?
9.47 I'm waiting for the promised connection to nuclear physics in any useful way for this audience.
9.50 Questions. Modifying gravity is asked about. Its is more complicated, but it can be made to explain observations - this is a little different to what was said earlier.
9.52 Carlos asks about the black hole contribution to dark matter. The black hole mas in the universe is rather uncertain.
9.54 Some English dude asks about the Type Ia supernovae data - that the data, by eye, appears to be consistent with no-dark energy as well as dark energy. He agrees, but statistically, when combined with other data, it favors dark energy. So its no good on its own, apparently.
9.56 Unbelievable - the same English dude has sneaked a second question in. He asks about the reason for the historical preference for dark matter rather than MOND. Why has, overwhelmingly, so much more effort has been devoted to dark matter than modifying gravity? Is it philosophical? The answer refers to modern evidence, which rather misses the point.
9.58 The English guy has finally shut up, and the talk ends.
9.05 He is not a nuclear physicist - he's a cosmologist.
9.06 The beginning of dark energy: Einstein's famous 'greatest mistake'- the cosmological constant introduced into his gravitational field equations to give a static universe. By doing this he missed the opportunity to theoretically predict the expanding universe discovered by Hubble in 1929 from redshifted spectral lines from galaxies. Einstein really was a bit dim, wasn't he?
9.11 Hubble expansion implies an age of the universe of 14Gyr. Completely wrong of course - Genesis tells us it's only around 6,000 yrs old. I've seen the dinosaur footprints next to the human footprints.
9.13 Need an accelerating universe to give an age of universe greater than 10Gyr. This is puzzling to me - from my cosmology course I distinctly remembering solving the Friedmann-Robertson-Walker equations and getting a universe age of 13Gyr without any dark energy. Hmmmm...
9.14 And now the FRW equations and EoS of the universe are flashed up. We're introduced to omegas:
Omega_m - density of matter/critical density of matter
Omega_e - density of dark energy/critical density of matter
9.16 Critical density: smaller - expand forever, greater - collapses at some point. This is without dark energy.
9.17 Dark energy has already been assumed to exist. Evidence to follow...
9.20 Primordial nucleosynthesis, when T < 0.1MeV. From nucleosynthesis, we can derive that 5% of matter density of universe is baryonic.
9.24 Cosmic Microwave Background is shown. Most perfect black body spectrum known. Not totally perfect though, there are observed temperature fluctuations due to density fluctuations in the plasma of the early universe.
9.25 Size of fluctuations consistent with flat universe.
9.26 These fluctuations are responsible for large scale structure formation - we can see their echo in the distribution of galaxies.
9.27 I get the feeling that the speaker is going for a shock and awe approach to the talk. Cosmologists do simulations with more particles than there are people on Earth!
9.29 Here comes the Type Ia SN evidence. He skips over the fact that the data appears consistent with no dark energy as well as dark energy.
9.31 Dark matter! Evidence: rotation curves of galaxies. He mentions changing gravity, but this doesn't work in explaining galaxy cluster collisions (e.g. the Bullet cluster). I have been to talks by Modified Gravity people claiming that it can.
9.36 The next slide loses me, partly because I missed the definition of the 'w' parameter which tells us about the dark energy EoS. 9.37 More long equations. Shock and awe.
9.38 Not natural to have w = constant, apparently. Indeed, it's illegal in 13 states in the US.
9.39 What the ?&$%? I wouldn't want to look at that slide on hallucenogenics. I'm stuggling with just coffee.
9.40 I have absolutely no idea what these domain wall networks are. But they can provide dark energy.
9.41 Relativistic and non-relativistic colored splotches are shown. They both look the same. Nevertheless one is ruled out.
9.42 Unified dark matter and dark energy! What are we going to call this unholy union?
9.45 The Planck satellite is going to constrain some of this stuff by measuring the CMB to unprecedented accuracy.
9.46 Summary: everything is known, except for what is dark matter and dark energy?
9.47 I'm waiting for the promised connection to nuclear physics in any useful way for this audience.
9.50 Questions. Modifying gravity is asked about. Its is more complicated, but it can be made to explain observations - this is a little different to what was said earlier.
9.52 Carlos asks about the black hole contribution to dark matter. The black hole mas in the universe is rather uncertain.
9.54 Some English dude asks about the Type Ia supernovae data - that the data, by eye, appears to be consistent with no-dark energy as well as dark energy. He agrees, but statistically, when combined with other data, it favors dark energy. So its no good on its own, apparently.
9.56 Unbelievable - the same English dude has sneaked a second question in. He asks about the reason for the historical preference for dark matter rather than MOND. Why has, overwhelmingly, so much more effort has been devoted to dark matter than modifying gravity? Is it philosophical? The answer refers to modern evidence, which rather misses the point.
9.58 The English guy has finally shut up, and the talk ends.
Wednesday, August 11, 2010
PASI 2012: rotten tomatoes?
The discussion began with a complaint about a theory slide from yesterday's talks: an equation with 24 terms? why on earth put it there and dedicate 6 seconds to explain it? Are our standards for presentations so achanchados that we tolerate such persistent background of bad talks? How much do we value properly communicating our good science at a conference?
We were just a sample of the young scientists in the conference happily chatting over some half finished dishes of camarao. We let our imagination fly and set to change the world, and the PASI 201X slowly took shape.
The first idea was to have a second projector showing live tweeter comments from the audience. I liked it even if I despise tweeter. Of course, a big loud buzz going off when time is over is essential, just to show the speaker who is in charge. And what if we give 'clickers' to the audience and poll them as the talk goes on? A trap door in the stage would open when the approval rating reaches the level of Italian politicians, sending a surprised speaker into a swimming pool. Maybe we should just give the audience control of advancing the slides. They could decide to halt the presentation in those absurdly complicated slides until the speaker has gone through the torture of explaining every detail. Clickers and technology are out there, power to the people!
Shall we replace session chairs, and their fluctuating skills, with a panel of multidisciplinary experts with the authoritative and intimidatory powers of a thesis defense committee, or of supreme court judges? They would be able to exert enough force to keep even the most reputable figures of our community on track, and discussing topics interesting to the bulk of the audience.
The draft of the plan, which might or might not involve some sort of "last physicist standing" element, is now on the hands of Meredith. I can not reveal more details so as not to interfere with the grant writing process, but we only have to finalize a few things here and there. For example, do we apply to the NSF, or to the Discovery Channel? They need a show to replace the aging MythBusters!
PS: today Ed Brown showed us the way speakers can strike back: Quizes.
Talk-delayed blog post emission
My apologies to Valdir Guimaraes for this late post, but I was busy selfishly tending to my own interests. Valdir told us about Light Radioactive Nuclei Capture Reactions By Phenomenological Potential models. The point of this talk was to demonstrate the importance of knowing capture cross-sections on light nuclei and show us how he can use a potential model based indirect data as well as direct data on neighbouring nuclei to make predictions for these cross-sections.
The light nuclei Valdir is referring to give us insight on light halo nuclei (e.g. 11Li and 11Be) as well as the A=8 gap present in cosmic abundances (e.g. 8Li 8B). Capture cross sections on light nuclei can effect early r-process nucleosynthesis, the pp-chain in the sun, as well as yields for big bang nucleosynthesis. Unfortunately I have to disagree with a point made by Valdir on the motivation for BBN. He said that observed abundances of 4He, 3He, 2H, and 7Li disagree with experimental capture cross sections, but this is actually only true for 7Li. Initially it was thought that all disagreed, but more careful approaches to observation have proved only 7Li disagrees with current nuclear knowledge (see R. Cyburt's lecture on BBN at http://www.nscl.msu.edu/~cyburt).
Ingredients in Valdir's potential model are the spectroscopic factor, the bound state potential, and the scattering potential. Each of these pieces of information are extracted from various pieces of experimental data, e.g. the spectroscopic factor can be obtained from data on transfer reactions. Valdir showed us a few examples of how his potential model accurately reproduced known capture cross-section data and it seems his model does quite a good job. However, maybe I missed them but I didn't see any predictions for less well known cross sections or the impact of these predictions. Without any interesting predictions, the potential model certainly loses the sexy-factor that comes with predictive power.
The light nuclei Valdir is referring to give us insight on light halo nuclei (e.g. 11Li and 11Be) as well as the A=8 gap present in cosmic abundances (e.g. 8Li 8B). Capture cross sections on light nuclei can effect early r-process nucleosynthesis, the pp-chain in the sun, as well as yields for big bang nucleosynthesis. Unfortunately I have to disagree with a point made by Valdir on the motivation for BBN. He said that observed abundances of 4He, 3He, 2H, and 7Li disagree with experimental capture cross sections, but this is actually only true for 7Li. Initially it was thought that all disagreed, but more careful approaches to observation have proved only 7Li disagrees with current nuclear knowledge (see R. Cyburt's lecture on BBN at http://www.nscl.msu.edu/~cyburt).
Ingredients in Valdir's potential model are the spectroscopic factor, the bound state potential, and the scattering potential. Each of these pieces of information are extracted from various pieces of experimental data, e.g. the spectroscopic factor can be obtained from data on transfer reactions. Valdir showed us a few examples of how his potential model accurately reproduced known capture cross-section data and it seems his model does quite a good job. However, maybe I missed them but I didn't see any predictions for less well known cross sections or the impact of these predictions. Without any interesting predictions, the potential model certainly loses the sexy-factor that comes with predictive power.
Brad's FRIB
Longest. Blog. Ever!
Asked what he thought of being blogged/taped as he prepared- Bad Bad Brad Sherrill said he was more concerned about bloggers harping on mistakes or jokes in the talk. How prescient. The live audience seems to be more of a threat than the bloggers, though. I wonder which jokes didn’t make the cut.
Here’s his plan: lay out the beam production mechanisms, discuss some fundamental symmetries you can test with those beams, and then round out the 45 minutes with societal applications and benefits from rare isotope facilities. This is not 100% FRIB, as I thought, but more a picture of where FRIB fits in the (modern) RIB facilities.
This is ambitious and a nice complement for a program that is riddled with a good number of speakers who haven’t fully embraced the spirit of reaching beyond our own special little corner in science.
15.05 Baha points out Brad’s tongue slip of identifying the protons as neutrons.
15.08 9 is less than 8. Ernst finds the new nucleus: Z=7 flourine. Congratulations, Ernst. But you don’t get to name it. Ernstinated toothpaste just sounds weird.
15.11 List of production mechanisms. Promises resources for the wiki. I must recruit him. Cha-ching for the Rare Isotope Facilities working group! The trick is to get all these promises made during the talks to be realized in the next week before people stop working on it.
15.12 List of good mechanisms for producing nuclei close to stability. (p,n), (p,nn) Also, fusion evaporation has large cross section. Good to know.
15.13 Fusion-fission!! 238U+12C fizzes to heavier isotopes—laser acceleration in the future. Good for getting nuclear physics on the movie screen. Lasers are camera friendly. How does one get the job of being a consultant for Hollywood?? That is never covered in physics career services….
15.15 Brad is doing the math in his head for 3He(58Ni,60Zn)n real quick. It quickly washes over his face that (58Ni,60Zn)n is ok. I enjoyed some of the finer details of production concerns for different types of nuclei. Having spent so much time at the NSCL, I have had a hard time wrapping my head around what happens at other types of facilities.
15.18 On to higher energy production mechanisms.
15.20 Spallation (wiki commons file shown) Ooo- video! It is just like fragmentation, except you get the beam nucleus from the target instead of the primary beam.
15.22 Shows range of isotopes you get for given processes. Nice to see what you will get at what facilities without having to look up a table. It is not quite second nature to me yet. But soon we will have the wiki. Hendrik will see to that.
15. 25 Explains abrasion and oblation terms and fills in details of fragmentation process. I hate abrasion/oblation talks and all their terminology. Brad confirms my suspicion that those talks employ unnecessary mystery about what they are doing.
15.28 He is behind schedule. I am worried he won’t get through all three sections. He is still in the first! One too many production curves, Brad.
15.29 Q_g term name- historical, and now I want to know the story. Probably a let down. Q_g is binding energy between beam and fragment (ME(beam) – ME(frag)). Production cross sections tell you about how well mass models are doing. Ah. That excited a few people in the room.
15.32 He’s screwed. No way he has enough time. I’ve never seen this before from Brad.
15.35 In 1966, 1000 know isotopes. Now, around 3000.
15.38 He’s referencing my jargon page. Must steal his pictures for jaron page in the name of my (non)working group page.
15.39 Reminds us the efficiencies are an important factor in getting a good intensity beam. True dat.
15.43 Good map. Going to steal that, too. This talk is more reconnaissance for me….
15.45 Holy crap—2E13 particles from U fission!!!
15.46 LISE++ advertisement.
15.49 Rap- You can thank Zach Meisel. YouTube making its entrance into the physics conference world. Fun at Brad’s expense. Good sport.
15.50 Still sorry he didn’t get to symmetries and societal impact as promised. Turns out- Brad is a tease.
Overtime: So when do you think FRIB will see first light? Brad: 2018. I’ll be starting a pool on how far behind schedule they ultimately go. Cash only.
15.54 Dying to AutoTune Brad Sherrill’s talk. Any suggestions on the music? Would be better if there were video of Brad talking.
15.55 Questions- finally. Discussion includes high vs. low energy experiment, the 6-12 months dead time between the NSCL turning off and FRIB turning on; a new hire Oscar at the NSCL to look at correlations in Beta decay for new physics in the weak interactions; doing EDM measurements an order of magnitude beyond TRIUMF. Baha wants the latter in writing: Done.
Asked what he thought of being blogged/taped as he prepared- Bad Bad Brad Sherrill said he was more concerned about bloggers harping on mistakes or jokes in the talk. How prescient. The live audience seems to be more of a threat than the bloggers, though. I wonder which jokes didn’t make the cut.
Here’s his plan: lay out the beam production mechanisms, discuss some fundamental symmetries you can test with those beams, and then round out the 45 minutes with societal applications and benefits from rare isotope facilities. This is not 100% FRIB, as I thought, but more a picture of where FRIB fits in the (modern) RIB facilities.
This is ambitious and a nice complement for a program that is riddled with a good number of speakers who haven’t fully embraced the spirit of reaching beyond our own special little corner in science.
15.05 Baha points out Brad’s tongue slip of identifying the protons as neutrons.
15.08 9 is less than 8. Ernst finds the new nucleus: Z=7 flourine. Congratulations, Ernst. But you don’t get to name it. Ernstinated toothpaste just sounds weird.
15.11 List of production mechanisms. Promises resources for the wiki. I must recruit him. Cha-ching for the Rare Isotope Facilities working group! The trick is to get all these promises made during the talks to be realized in the next week before people stop working on it.
15.12 List of good mechanisms for producing nuclei close to stability. (p,n), (p,nn) Also, fusion evaporation has large cross section. Good to know.
15.13 Fusion-fission!! 238U+12C fizzes to heavier isotopes—laser acceleration in the future. Good for getting nuclear physics on the movie screen. Lasers are camera friendly. How does one get the job of being a consultant for Hollywood?? That is never covered in physics career services….
15.15 Brad is doing the math in his head for 3He(58Ni,60Zn)n real quick. It quickly washes over his face that (58Ni,60Zn)n is ok. I enjoyed some of the finer details of production concerns for different types of nuclei. Having spent so much time at the NSCL, I have had a hard time wrapping my head around what happens at other types of facilities.
15.18 On to higher energy production mechanisms.
15.20 Spallation (wiki commons file shown) Ooo- video! It is just like fragmentation, except you get the beam nucleus from the target instead of the primary beam.
15.22 Shows range of isotopes you get for given processes. Nice to see what you will get at what facilities without having to look up a table. It is not quite second nature to me yet. But soon we will have the wiki. Hendrik will see to that.
15. 25 Explains abrasion and oblation terms and fills in details of fragmentation process. I hate abrasion/oblation talks and all their terminology. Brad confirms my suspicion that those talks employ unnecessary mystery about what they are doing.
15.28 He is behind schedule. I am worried he won’t get through all three sections. He is still in the first! One too many production curves, Brad.
15.29 Q_g term name- historical, and now I want to know the story. Probably a let down. Q_g is binding energy between beam and fragment (ME(beam) – ME(frag)). Production cross sections tell you about how well mass models are doing. Ah. That excited a few people in the room.
15.32 He’s screwed. No way he has enough time. I’ve never seen this before from Brad.
15.35 In 1966, 1000 know isotopes. Now, around 3000.
15.38 He’s referencing my jargon page. Must steal his pictures for jaron page in the name of my (non)working group page.
15.39 Reminds us the efficiencies are an important factor in getting a good intensity beam. True dat.
15.43 Good map. Going to steal that, too. This talk is more reconnaissance for me….
15.45 Holy crap—2E13 particles from U fission!!!
15.46 LISE++ advertisement.
15.49 Rap- You can thank Zach Meisel. YouTube making its entrance into the physics conference world. Fun at Brad’s expense. Good sport.
15.50 Still sorry he didn’t get to symmetries and societal impact as promised. Turns out- Brad is a tease.
Overtime: So when do you think FRIB will see first light? Brad: 2018. I’ll be starting a pool on how far behind schedule they ultimately go. Cash only.
15.54 Dying to AutoTune Brad Sherrill’s talk. Any suggestions on the music? Would be better if there were video of Brad talking.
15.55 Questions- finally. Discussion includes high vs. low energy experiment, the 6-12 months dead time between the NSCL turning off and FRIB turning on; a new hire Oscar at the NSCL to look at correlations in Beta decay for new physics in the weak interactions; doing EDM measurements an order of magnitude beyond TRIUMF. Baha wants the latter in writing: Done.
Simulation of Silicon Detector Response
It was increadible how Zach looked like very calm during his presentation. He had changed a little the title of his talk, but he could show the results of the simulations using GEANT4 for the response of a DSSD detector comparing with experimental data. And he did propaganda of Marcelo's talk on Thursday. I don1t knowif Marcelo was expecting it. : )
6He+9Be reaction
This was one of the student seminars and Kelly did a very good presentation. In the beginning she was a little nervous, like all the students when present their work in a different language and in front of too many professors. In her place, I would stay in a panic.
She talked about the study of 6He+9Be reaction, the experimental results obtained in Brazil and the theoretical predictions were made in colaboration with people from Seville, Spain.
She talked about the study of 6He+9Be reaction, the experimental results obtained in Brazil and the theoretical predictions were made in colaboration with people from Seville, Spain.
The Drinks of Brazil - Caipirinha
The Caipirinha is the national drink of Brazil. I have collected accounts of the Caipirinha being a good 'any time' drink to have in the morning, afternoon or night; However, if you drink too many in the morning you will be out like it's night. According to the International Bartenders Association it is made with 2 teaspoons of sugar 1/2 a lime and 5 cl of cachaça, although I doubt most bartenders measure that exactly. The Caipifruta replaces lime with some other fruit and sometimes adds condensed milk.
Tuesday, August 10, 2010
Break up in Buenos Aires
Alberto Pacheco presented what I found was the most clear description of break up reactions so far. Perhaps it was that I was blogging the talk and payed 'extra attention'. Perhaps it was that he restricted the explanations of break up to the bare essentials - referring to the talks from last week for additional information. It worked for me.
We learned how break up is a reaction when something breakups. We detect the pieces flying out, and from there we'd like to understand what happened. It's not so simple as it sounds. Experimentalists collect information on energy and momentum of the reaction products, in a limited set of detectors. This must be used to reconstruct how the reaction proceed (with SUPERKINETICO code), and understand which of the many alternative processes we group in the breakup bag took place. Understanding breakup is an advancement of science in itself, but it also contributes to fields such as astrophysics (better understanding of capture reactions through Coulomb dissociation), and reaction theory (to enhance or reduce fission by breakup? such is the question).
He showed results for 6Li+144Sm, and 7Li+144Sm, but I missed what the results had to say about the aforementioned questions. It would also had been nice to have some words about the Tandar lab, which I think was for the first time a main character in the plot.
We learned how break up is a reaction when something breakups. We detect the pieces flying out, and from there we'd like to understand what happened. It's not so simple as it sounds. Experimentalists collect information on energy and momentum of the reaction products, in a limited set of detectors. This must be used to reconstruct how the reaction proceed (with SUPERKINETICO code), and understand which of the many alternative processes we group in the breakup bag took place. Understanding breakup is an advancement of science in itself, but it also contributes to fields such as astrophysics (better understanding of capture reactions through Coulomb dissociation), and reaction theory (to enhance or reduce fission by breakup? such is the question).
He showed results for 6Li+144Sm, and 7Li+144Sm, but I missed what the results had to say about the aforementioned questions. It would also had been nice to have some words about the Tandar lab, which I think was for the first time a main character in the plot.
Review: Rare isotopes experiments at FAIR
Tom Auman gave a very exciting talk about the status of rare isotopes experiments at FAIR and I will post some topics that I could remember.
FAIR is a project that will start next year in GSI and will enable new experiments to measure giant resonances in rare isotopes. In particular, experiments to measure the giant quadrupole resonances of rare isotopes that have not been done so far, will be studied by systematic apha scattering. The nucleus is excited by the absorption of virtual photons of the strong electric field of a heavy nucleus and the determination of the photon energy (excitation energy) is done via the measurement of the complete kinematics of the outgoing particles event by event.
He showed the experiment setup at GSI including the LAND (large area neutron detector with a high efficiency of ~90% at 600 MeV) and ALADIN (large acceptance dipole). This new setup will provide measurements of excitation energies with resolution of 20keV.
He showed results for the dipole strenght distribution in neutron rich Sn isotopes and pointed out that limitations in the experiment come from the maximum charge limit in the storage ring (ESR). He comment that beam intensities will be less than in MSU but the energies will be larger.
FAIR is a project that will start next year in GSI and will enable new experiments to measure giant resonances in rare isotopes. In particular, experiments to measure the giant quadrupole resonances of rare isotopes that have not been done so far, will be studied by systematic apha scattering. The nucleus is excited by the absorption of virtual photons of the strong electric field of a heavy nucleus and the determination of the photon energy (excitation energy) is done via the measurement of the complete kinematics of the outgoing particles event by event.
He showed the experiment setup at GSI including the LAND (large area neutron detector with a high efficiency of ~90% at 600 MeV) and ALADIN (large acceptance dipole). This new setup will provide measurements of excitation energies with resolution of 20keV.
He showed results for the dipole strenght distribution in neutron rich Sn isotopes and pointed out that limitations in the experiment come from the maximum charge limit in the storage ring (ESR). He comment that beam intensities will be less than in MSU but the energies will be larger.
Mass ejection in protoneutron star induced by neutrino burst
Luis Gustavo gave a nice talk about protoneutron stars and the the role played by the neutrinos in mass ejection. He used the Equation of State (EOS) to conclude that neutrino pressure and momenta must act together in order to see noticeable mass ejection, of about 2% of the total mass.
Students taking careful notes
The youngest PASI student and aspiring "big person," Sophie, took careful notes (seen here is a page from the stellar burning section) during Ani's talk on the origin of the elements Monday morning. Sophie confessed to only paying attention to the first half before succombing to the daydreams of other more tantilizing ideas. When asked what could be more exciting than the origin of the elements, Sophie confessed, "I don't know," turned, and left. Refreshing honesty.
The Drinks of Brazil - Chimarrão
By popular demand chimarrão. Now anybody who has been around someone from Argentina, Uruguay, or Paraguay would say that's just mate, and they would be right. Chimarrão is like tea in inverse kinematics, lots of leaves form the erva mate plant (yerba mate plant in Spanish) with only a little bit of hot water. Special equipment is needed to drink chimarrão. A dried gourd known as a cuia, is used as a cup with a special metal straw, called a bomba, that has a strainer at one end. It is usually drunk in social gatherings passing the gourd around and people taking a sip from the straw. It is predominantly drunk in the south of Brazil, however a variant of the drink is served in the Brazilian state of Mato Grosso Sul where it is made with cold water and known as tererê.
Time is never time at all
Neelima Kelkar presented a different perspective into the problem of alpha decay. This comes courtesy of the 'dwell time', which is the time a particle spends inside a barrier in the quantum tunneling problem we all came to love in our quantum mechanics classes. After some quasi-philosophical questions on the meaning of time on such microscopic situation, the talk went on with a lot of formulas and derivations that made me felt we had the famous V.Z giving the talk (my QM professor; fortunately the lecture was not followed by one of his infamous homework assignments!). The derivations converged on the identity between dwell time and the Wigner width of the state the system decays to (or is it decay from?), thus dwell time is a elegant concept nicely related to alpha decay. How, why, what else can we learn from it, that it help in other types of decays?? There was lively discussion about it in the question session. The answers won't be found on this post, but with Neelima in one of the coffee breaks
There talk also presented a journey from the literature in the field, starting in the 1930's and explaining the main results and controversies in about 50 papers most of us PASIParticipants will never read. But if you must read one: Asher Peres, Am J Phys 48 552 (1980). What is a clock? But beware the conclusions about the demise of Hamiltonian quantum mechanics; they have been proved wrong.
There talk also presented a journey from the literature in the field, starting in the 1930's and explaining the main results and controversies in about 50 papers most of us PASIParticipants will never read. But if you must read one: Asher Peres, Am J Phys 48 552 (1980). What is a clock? But beware the conclusions about the demise of Hamiltonian quantum mechanics; they have been proved wrong.
Stripping cross-sections
10.04 Good Morning.
10.05 Cladio deConti is now talking about Pauli Blocking and in-Medium Effects in Nucleon Knockout Reactions.
10.07 I think I need a new pair of glasses to see the introduction.
10.08 Focusing on symmetric nuclear matter, he's studying how the medium modifies nucleon knowckout reaction cross-sections. Such reactions are used to study single particle structure in nuclei.
10.09 It appears (correct me if I'm wrong) that several methods are used - Pauli blocking, Brueckner, and a Hartree-Fock (phenomenological) treatment. Brueckner presumably includes Pauli blocking.
10.10 Approximation: free NN cross-section is isotropic.
10.11 A simple parameterization of the cross-section is shown (I think for the Brueckner treatment). I think simple is a relative term.
10.12 The stripping cross-section is displayed. I had something else in mind other than what is actually shown.
10.13 I'm still thinking about stripping cross-sections.
10.14 So the initial state is before the clothes come off? And the final state....?
10.14 + 30secs And Pauli blocking is something to do with a large Italian bouncer throwing an over-enthusiastic customer out?
10.15 Results! pn cross-sections are displayed. The cross-sections from including Pauli-blocking, and from Brueckner theory, both appear to agree well at low scattering energies, but Brueckner diverges at high energies. They both are lower than the free cross-section at low energies. The phenomenological treatment is close to the free cross-section - so it doesn't include Pauli-blocking?
10.22 The results are applied to some reactions. I picked the wrong talk to sit right at the back of the room.
10.23 Results for stripping diffraction dissociation. Sounds like something you'd find in a David Lynch film.
10.25 My mistake - stripping, diffraction, and dissocation are three seperate processes.
10.27 Conclusions. My eyes hurt.
10.28 Medium modifications are more pronounced in halo nuclei than more bound nuclei.
10.29 Stripping follows nucleon-nucleon cross-sections from model to model.
10.30 Discussion follows about whether the Brueckner's high energy behavior is an artifact or physical. I don't catch the conclusion.
10.33 Questions are certainly lively! Must be all the talk of stripping.
10.35 And we're done. Coffee and a wet towel over the eyes are now in order.
10.05 Cladio deConti is now talking about Pauli Blocking and in-Medium Effects in Nucleon Knockout Reactions.
10.07 I think I need a new pair of glasses to see the introduction.
10.08 Focusing on symmetric nuclear matter, he's studying how the medium modifies nucleon knowckout reaction cross-sections. Such reactions are used to study single particle structure in nuclei.
10.09 It appears (correct me if I'm wrong) that several methods are used - Pauli blocking, Brueckner, and a Hartree-Fock (phenomenological) treatment. Brueckner presumably includes Pauli blocking.
10.10 Approximation: free NN cross-section is isotropic.
10.11 A simple parameterization of the cross-section is shown (I think for the Brueckner treatment). I think simple is a relative term.
10.12 The stripping cross-section is displayed. I had something else in mind other than what is actually shown.
10.13 I'm still thinking about stripping cross-sections.
10.14 So the initial state is before the clothes come off? And the final state....?
10.14 + 30secs And Pauli blocking is something to do with a large Italian bouncer throwing an over-enthusiastic customer out?
10.15 Results! pn cross-sections are displayed. The cross-sections from including Pauli-blocking, and from Brueckner theory, both appear to agree well at low scattering energies, but Brueckner diverges at high energies. They both are lower than the free cross-section at low energies. The phenomenological treatment is close to the free cross-section - so it doesn't include Pauli-blocking?
10.22 The results are applied to some reactions. I picked the wrong talk to sit right at the back of the room.
10.23 Results for stripping diffraction dissociation. Sounds like something you'd find in a David Lynch film.
10.25 My mistake - stripping, diffraction, and dissocation are three seperate processes.
10.27 Conclusions. My eyes hurt.
10.28 Medium modifications are more pronounced in halo nuclei than more bound nuclei.
10.29 Stripping follows nucleon-nucleon cross-sections from model to model.
10.30 Discussion follows about whether the Brueckner's high energy behavior is an artifact or physical. I don't catch the conclusion.
10.33 Questions are certainly lively! Must be all the talk of stripping.
10.35 And we're done. Coffee and a wet towel over the eyes are now in order.
Trapped in quantum many body physics
I must confess that I have not attended Rotureau's talk on effective field theory for few-
fermion systems, but I "interviewed" some PASI students and I managed to get the slides :) So, when I read the title, I thought his would would have something to do with the kind of work I do with ion traps. Not really. Maybe the theorist bloggers have something to say?
fermion systems, but I "interviewed" some PASI students and I managed to get the slides :) So, when I read the title, I thought his would would have something to do with the kind of work I do with ion traps. Not really. Maybe the theorist bloggers have something to say?
Monday, August 9, 2010
Rodizio Dinner this Wednesday
Let´s get together this Wednesday and have dinner at a very nice restaurant rodizio style. They have by far the best picanha (sirloin steak) we tried in Joao Pessoa and also an excellent sushi and sashimi buffet.
The place is called Picanha do Basto´s praia and the address is 705, Rua Professora Maria Sales. It costs about R$25 per person. If you are interested we will meet at the lobby of the hotel at 7:30pm.
See you there!
The place is called Picanha do Basto´s praia and the address is 705, Rua Professora Maria Sales. It costs about R$25 per person. If you are interested we will meet at the lobby of the hotel at 7:30pm.
See you there!
The start of a new week: Baha Balantekin + Ernesto Mane
We began the second week on the conference with neutrinos from Baha Balantekin, and laser spectroscopy from Ernesto Mane.
Prof. Balantekin gave one of the best review talks of he conference so far. He started with an historical introduction to neutrino astrophysics: Davis, Bahcal, the ancient solar neutrino problem. It turns out there's still life in it, arising from inconsistencies betwen observations in helioseismologic (the bubble behaviour of the sun) and the sun composition. It would require precision measurements of CNO neutrinos (precision+neutrino experiments: good luck with that!). The talk then flashed a bit too fast through neutrino experiments, but we were treated with pictures of SUPERKAMIOKANDE and some clasic experimental spectra: oscillation of atmospheric neutrinos, the few counts that made neutrino emissions from core collapse supernovae an experimental fact.
Theory was smartly introduces with slides written in "Comic Sans" font; it created a great illusion of simplicity for the derivations with Lagrangians and dimensional countings. Unfortunately, almost five six since my last classical mechanics class the difference between a Lagrangian and a Hamiltonian has long evaporated from my mind! From the derivations we arrived at the fact that a massive neutrino can be somewhat expressed in the simplest possible way within the standard model (exactly how was beyond me), so another of their properties is they obbey Ocham's razor. With the mass arrived their mixing angles (we'd ove to know theta13), and how all we ignore about neutrinos permeates everything from the matter-antimatter asymmetry to the electron fraction in the ejected material during core collapse supernovae.
A revolution is in the making in enormous underwater tanks and theorist's brains!
Then it was the turn of the local hero, Dr. Mane. He began explaining all things we can learn from shining lasers into radioactive ions, such as charge radii, magnetic moments, nuclear exited states. It followed with what I thought was a unnecessarily pessimistic picture of the experimental challenges in laser spectroscopic experiments... we need millions and millions of atoms! But it turns out he had a few cards to puled out of his sleeve and solve those problems with ion traps in the experimental setup!
The tricks: with a gas filled Pauli trap you can control bunch the beam (i.e. cotrol when you send the atoms out of the trap and into the light) and that reduces background greatly because you only listen to the detectors at that time. Fill the trap with gas and the atoms beam is restricted to smaller region of space, and has less spread in velocities (low low emitance). Thus better resolution. And finally just pump up the atoms when they're still in the trap (better efficiency!) and you can call yourself a laser spectroscopy magician.
In summary, I got the impression lasser spectroscopy is a field with a lot of activity (CERN, Finland, TRIUMF), and with more people jumping in the wagon soon (NSCL, ANL, one more), which promises lots of experimental results in the years to come.
Prof. Balantekin gave one of the best review talks of he conference so far. He started with an historical introduction to neutrino astrophysics: Davis, Bahcal, the ancient solar neutrino problem. It turns out there's still life in it, arising from inconsistencies betwen observations in helioseismologic (the bubble behaviour of the sun) and the sun composition. It would require precision measurements of CNO neutrinos (precision+neutrino experiments: good luck with that!). The talk then flashed a bit too fast through neutrino experiments, but we were treated with pictures of SUPERKAMIOKANDE and some clasic experimental spectra: oscillation of atmospheric neutrinos, the few counts that made neutrino emissions from core collapse supernovae an experimental fact.
Theory was smartly introduces with slides written in "Comic Sans" font; it created a great illusion of simplicity for the derivations with Lagrangians and dimensional countings. Unfortunately, almost five six since my last classical mechanics class the difference between a Lagrangian and a Hamiltonian has long evaporated from my mind! From the derivations we arrived at the fact that a massive neutrino can be somewhat expressed in the simplest possible way within the standard model (exactly how was beyond me), so another of their properties is they obbey Ocham's razor. With the mass arrived their mixing angles (we'd ove to know theta13), and how all we ignore about neutrinos permeates everything from the matter-antimatter asymmetry to the electron fraction in the ejected material during core collapse supernovae.
A revolution is in the making in enormous underwater tanks and theorist's brains!
Then it was the turn of the local hero, Dr. Mane. He began explaining all things we can learn from shining lasers into radioactive ions, such as charge radii, magnetic moments, nuclear exited states. It followed with what I thought was a unnecessarily pessimistic picture of the experimental challenges in laser spectroscopic experiments... we need millions and millions of atoms! But it turns out he had a few cards to puled out of his sleeve and solve those problems with ion traps in the experimental setup!
The tricks: with a gas filled Pauli trap you can control bunch the beam (i.e. cotrol when you send the atoms out of the trap and into the light) and that reduces background greatly because you only listen to the detectors at that time. Fill the trap with gas and the atoms beam is restricted to smaller region of space, and has less spread in velocities (low low emitance). Thus better resolution. And finally just pump up the atoms when they're still in the trap (better efficiency!) and you can call yourself a laser spectroscopy magician.
In summary, I got the impression lasser spectroscopy is a field with a lot of activity (CERN, Finland, TRIUMF), and with more people jumping in the wagon soon (NSCL, ANL, one more), which promises lots of experimental results in the years to come.
A theory for all nuclei, ever?
NOTE: Apologies for the length of this blog, but the talk was quite an epic.
My hobby: going to physics talks by both members of a classic physics textbook authoring double act. It's my equvalent of autograph hunting. Today I complete the Ring and Schuck collection I started four years ago when I saw Peter Schuck talk at Orsay.
I've also completed the Hawking and Ellis set (Large Scale Structure of Space-Time). I think that might be it for two-authored texts. I must try and see Walter "must beat Landau" Greiner sometime, which automatically covers about 411 textbooks.
Anyone else seen any interesting textbook authors? Anyone else care?
15.03 So Peter Ring is talking on "Density Functional Theory in Nuclear Physics". And he's off.
15.04 Goal: a theory that covers the whole nuclide chart. Simples.
15.04 A lot of astrophysicists' needs are flashed up for about two seconds. I didn't catch any, but I can come up with a few...
15.04 Ab-initio scales: >1GeV QCD, 200MeV for nucloeon and pion Lagrangian, 100keV density dependent effective nuclear forces > DFT!
15.06 Ring has set off at a furious pace. The familiar phenomenology of the bare nucleon-nucleon interaction comes and goes like a Mercedes at Hockenheim.
15.07 Nuclei are very small apparently. Try telling that to a friend of mine who was mugged by one walking back from the pub one night.
15.08 He means relative to the scale of the uncertainty relation; in comparison, molecular physics has a similar potential, but it is able to sit in the bottom of the attractive well since that well sits at distances much larger than those at which uncertainty becomes a problem.
15.09 Crikey.
15.10 Hohenberg-Kohn theorem - the remarkable theorem that the exact energy of a quantum mechanical many body system is a universal function of the local density. From this we can embark on the project of constructing such a functional for nuclear physics.
15.13 For a many body system in an external field, local density is a functional of potential, and we Legendre transform to get potential as a functional of density. The Legendre transform is explained with reference to transforming between thermodynamic variables, the most familiar use of such transforms.
15.15 This is breathless stuff. Can he keep up the pace, or has he come out of the gates too quickly? Stay tuned....
15.16 Hohenberg-Kohn gave a proof for the existence of their universal functional, but didn't tell us how to calculate it. Spoilsports.
15.18 the HK functional can be decomposed into the direct interaction part (the Hartree term), the non-interacting part and the exchange term (Fock term).
15.19 Thomas-Fermi approx. is a local density approx. - take density to be locally constant, and the non-interacting term is analytical. Usually gradient terms in density are added to make it work better. Still, shell effects are not included.
15.21 Kohn-Sham theory: Kohn is not done yet; together with the unfortunately named Sham, he added an auxiliary potential, which, in the Schrodinger equation, would give the exact density (which includes shell effects). Crazy, but nice!
15.23 By the way, the equations on the slides are color-coded: potentials and densities in red, wavefunctions and kinetic energy densities in blue, the rest black.
15.25 I think of wavefunctions as having a melancholy shade of azure.
15.26 We arrive at a Hartree-Fock like scheme. Except it's exact not an approximation to the ground state. Actually the Fock term isn't explicit - it's somewhere hiding in the local approximation. It's shy.
15.27 Condensed matter physicists rejoice: for Coulomb forces one now has the exact functional.
15.28 I catch something about going to the supermarket to purchase functionals. I usually find them between the pet food and paper towels.
15.30 Amusingly, the paper towels in the convenience store opposite the hotel have the brand name "Snob".
15.31 DFT in nuclei: We have Skyrmes, Gogny and RMF. We have spin, isospin, relativistic and pairing degrees of freedom. AND we have to perform all calcuations while suspended upside down over a crocodile infested pool while half-starved lions are projected towards us by catapult.
15.34 The slide with the catapulting lions was quite amusing.
15.35 Virtues of DFTs: self-consistency - deformations, shells, whether valence or not, universality (applicability over the whole nuclear chart) and taste good with or without whipped cream.
15.36 He's talking about Skyrmes, something I'm actually very familiar with. Now he's finished and moved on to relativistic mean field theory. Oh well, easy come easy go.
15.37 RMF has many advatages, not least among them covariance, connection to underlying theories (chiral theories, for example), more apparently physical coupling constants, self-consistent inclusion of spin-orbit term and a rather nice line in jaunty hats.
15.41 I was working on the beach the other day and employed the no-sea approximation. I almost drowned.
15.42 For a small fee, I'm available for weddings and bar-mitzvahs.
15.43 Let's compare a point-coupling RMF model with ab-initio. Excellent agreement with Baldo's results. (Baldo is a nuclear theorist, not the nickname of a follically challenged physicist). But it is sometimes necessary to fit to microscopic results.
15.44 Now it's time for the "running out of time so lets show 279 graphs in 3 minutes" part of the talk.
15.45 It was only two minutes. Now we're on to time-dependence. The Runge-Gross theorem is the time-dependent version of Kohn-Sham. Or Hohnberg-Kohn. Or Even Hohnberg-Sham. I'm losing track. Some nice slides of giant resonances in tin, (My master's thesis was on giant resonances in Argon isotopes using time-dependent Hartree-Fock, so I'm wallowing in nostalgia right now).
15.50 Interesting results for spin-isopsin resonances and beta decay. I would say more, but next time I look up he's covering supernova neutrino flux. Aaaargh!
15.52 Conclsion: DFT is VERY successful, though we're far from a microscopic derivation. Uncertainties are, among other things, the isospin dependence of the parameters (e.g. large isospin asymmetries?) and tensor forces.
15.53 The isospin dependence is raised as a problem in rare isoptopes for n or p-rich nuclei.
15.56 Interestingly, Ring says he doesn't understand the spin-orbit emergence from the simple Walecka RMF model.
15.58 Deriving the mean-field parameters from microscopic, or at least some hybrid microscopic-nuclear matter model, is ongoing.
16.04 And we're done. Breathe.
My hobby: going to physics talks by both members of a classic physics textbook authoring double act. It's my equvalent of autograph hunting. Today I complete the Ring and Schuck collection I started four years ago when I saw Peter Schuck talk at Orsay.
I've also completed the Hawking and Ellis set (Large Scale Structure of Space-Time). I think that might be it for two-authored texts. I must try and see Walter "must beat Landau" Greiner sometime, which automatically covers about 411 textbooks.
Anyone else seen any interesting textbook authors? Anyone else care?
15.03 So Peter Ring is talking on "Density Functional Theory in Nuclear Physics". And he's off.
15.04 Goal: a theory that covers the whole nuclide chart. Simples.
15.04 A lot of astrophysicists' needs are flashed up for about two seconds. I didn't catch any, but I can come up with a few...
15.04 Ab-initio scales: >1GeV QCD, 200MeV for nucloeon and pion Lagrangian, 100keV density dependent effective nuclear forces > DFT!
15.06 Ring has set off at a furious pace. The familiar phenomenology of the bare nucleon-nucleon interaction comes and goes like a Mercedes at Hockenheim.
15.07 Nuclei are very small apparently. Try telling that to a friend of mine who was mugged by one walking back from the pub one night.
15.08 He means relative to the scale of the uncertainty relation; in comparison, molecular physics has a similar potential, but it is able to sit in the bottom of the attractive well since that well sits at distances much larger than those at which uncertainty becomes a problem.
15.09 Crikey.
15.10 Hohenberg-Kohn theorem - the remarkable theorem that the exact energy of a quantum mechanical many body system is a universal function of the local density. From this we can embark on the project of constructing such a functional for nuclear physics.
15.13 For a many body system in an external field, local density is a functional of potential, and we Legendre transform to get potential as a functional of density. The Legendre transform is explained with reference to transforming between thermodynamic variables, the most familiar use of such transforms.
15.15 This is breathless stuff. Can he keep up the pace, or has he come out of the gates too quickly? Stay tuned....
15.16 Hohenberg-Kohn gave a proof for the existence of their universal functional, but didn't tell us how to calculate it. Spoilsports.
15.18 the HK functional can be decomposed into the direct interaction part (the Hartree term), the non-interacting part and the exchange term (Fock term).
15.19 Thomas-Fermi approx. is a local density approx. - take density to be locally constant, and the non-interacting term is analytical. Usually gradient terms in density are added to make it work better. Still, shell effects are not included.
15.21 Kohn-Sham theory: Kohn is not done yet; together with the unfortunately named Sham, he added an auxiliary potential, which, in the Schrodinger equation, would give the exact density (which includes shell effects). Crazy, but nice!
15.23 By the way, the equations on the slides are color-coded: potentials and densities in red, wavefunctions and kinetic energy densities in blue, the rest black.
15.25 I think of wavefunctions as having a melancholy shade of azure.
15.26 We arrive at a Hartree-Fock like scheme. Except it's exact not an approximation to the ground state. Actually the Fock term isn't explicit - it's somewhere hiding in the local approximation. It's shy.
15.27 Condensed matter physicists rejoice: for Coulomb forces one now has the exact functional.
15.28 I catch something about going to the supermarket to purchase functionals. I usually find them between the pet food and paper towels.
15.30 Amusingly, the paper towels in the convenience store opposite the hotel have the brand name "Snob".
15.31 DFT in nuclei: We have Skyrmes, Gogny and RMF. We have spin, isospin, relativistic and pairing degrees of freedom. AND we have to perform all calcuations while suspended upside down over a crocodile infested pool while half-starved lions are projected towards us by catapult.
15.34 The slide with the catapulting lions was quite amusing.
15.35 Virtues of DFTs: self-consistency - deformations, shells, whether valence or not, universality (applicability over the whole nuclear chart) and taste good with or without whipped cream.
15.36 He's talking about Skyrmes, something I'm actually very familiar with. Now he's finished and moved on to relativistic mean field theory. Oh well, easy come easy go.
15.37 RMF has many advatages, not least among them covariance, connection to underlying theories (chiral theories, for example), more apparently physical coupling constants, self-consistent inclusion of spin-orbit term and a rather nice line in jaunty hats.
15.41 I was working on the beach the other day and employed the no-sea approximation. I almost drowned.
15.42 For a small fee, I'm available for weddings and bar-mitzvahs.
15.43 Let's compare a point-coupling RMF model with ab-initio. Excellent agreement with Baldo's results. (Baldo is a nuclear theorist, not the nickname of a follically challenged physicist). But it is sometimes necessary to fit to microscopic results.
15.44 Now it's time for the "running out of time so lets show 279 graphs in 3 minutes" part of the talk.
15.45 It was only two minutes. Now we're on to time-dependence. The Runge-Gross theorem is the time-dependent version of Kohn-Sham. Or Hohnberg-Kohn. Or Even Hohnberg-Sham. I'm losing track. Some nice slides of giant resonances in tin, (My master's thesis was on giant resonances in Argon isotopes using time-dependent Hartree-Fock, so I'm wallowing in nostalgia right now).
15.50 Interesting results for spin-isopsin resonances and beta decay. I would say more, but next time I look up he's covering supernova neutrino flux. Aaaargh!
15.52 Conclsion: DFT is VERY successful, though we're far from a microscopic derivation. Uncertainties are, among other things, the isospin dependence of the parameters (e.g. large isospin asymmetries?) and tensor forces.
15.53 The isospin dependence is raised as a problem in rare isoptopes for n or p-rich nuclei.
15.56 Interestingly, Ring says he doesn't understand the spin-orbit emergence from the simple Walecka RMF model.
15.58 Deriving the mean-field parameters from microscopic, or at least some hybrid microscopic-nuclear matter model, is ongoing.
16.04 And we're done. Breathe.
The Drinks of Brazil – Nova Schin
Does this drink combine two great things, beer and explosive nucleosynthesis, into one? The answer is sadly no. When you drink Nova Schin instead of getting a stellar explosion of taste in you mouth you are greeted by something resembling Bud Light. The confusion comes from Portuguese being a romance language. When Tycho Brahe saw the supernova of 1572 in the sky he thought that it was a brand new star and so he called it stella nova which is Latin for new star. Since Portuguese is a romance language it descended from Latin and therefor the word for new, nova, is the same. So like New Coke this is New Schin, which begs the question what is Schin classic like?
very delayed blog on beta-delayed proton emission studies for nuclear astrophysics
Livius Trache told us some stories on measurements of reactions relevant to Hydrogen burning in novae and X-ray bursts. As mentioned in previous talks we need good nuclear physics data in order to link astronomical observations and nucleosynthesis models. His research group studies radiative capture reactions, such as (p,γ), (α,γ) and (n,γ). The interest lies on the determination of astrophysical S factors (remember that we measure cross sections, but we plot S).
We're mostly concerned with resonant reactions, which are two step processes: (1) formation of metastable state, (2) decay. The cross section given by Breit-Wigner and varies rapidly with energy and its contribution to the reaction rate depends on two factors: (1) location in energy, and (2) probability of occurrence. There are two big problems in this kind of studies first, that the reactions in stars involve radioactive nuclei, i.e. we need RIBs to produce them, and second, that the energies involved are low and the cross sections very small, therefore we need to use indirect methods.
Some indirect methods with RIBs introduced: Coulomb Dissociation, Transfer Reactions, Breakup of loosely bound nuclei, Spectroscopy of resonances, Decay spectroscopy, Trojan horse method.
One case of interest given as example is the 23Al decay to 23Mg (compound system). Also here comes the 22NA puzzle again: how does depletion of 22Na in novae happen? We can contibute by studying 22Mg(p,g) and 22Na(p,g) reactions. Livius et at conduct experiments at MARS, at Texas A&M University using inverse kinematics reactions such as (p,n), (p,2n), (p,3n), among others. We are shown technical details of the facility and experimental details, then some results: they found out that the 22Mg(p,g) reaction is not important for depletion of 22Na in novae since its cross section is too small and photodissociation happens quickly. They are also able to determine half-lives, branching ratios, a new value for the mass of 23Al, resonances in 23Mg, etc. It was very interesting to learn that very close lying resonances can be disentangled by using a very thin (~40 micrometer-thick) Si detector to measure beta-proton decays.
3 nucleons are stronger than 2, says Feynman
It's written in the Feynman lectures in physics. The story goes that Sir Richard took the task of preparing a lecture on spin as a challenge from a colleague, but quickly found the big challenges of the endeavor. One of the mantras behind his lecture series was "if we really understand a topic in Physics we should be able to explain it at a level accessible to undergraduates". It seems he still didn't fully comprehend spin.
Contrast that to the instructions we received from the organizers as you might find in the PASI webpage: make a presentation at the Advanced Undergraduate level, and spend like 75% of the talk discussing the open questions in the topic. A clear clash with Feynman's ideas! So lets be fair to the speakers in this my first lecture blog (it took only a week!). Most have made the effort to keep talks at the students level; at least for the first few slides. There were of course a few who couldn't resist and showed off their results right from the start, even though I think we're not the most receptive audience for that kind of stuff... but I digress.
Achim Schwenk talk last Friday started at the (graduate) student level; or so it seemed to my highly under-caffeinated and under-slept experimentalist mind*. The main clear message was: 3-body forces are frontier, they impact the structure and existence of neutron-rich nuclei and neutron-rich matter in astrophysics. Very easy to get it, as it was written explicitly in the second slide.
The highest point of Achim's advanced undergraduateness was a intuitive explanation of three body forces with such mundane objects as the sun, and the moon, and the tides. But we know intuitive explanations can only take us so far in nuclear physics, so soon we were dealing with pion exchange, V_low,k, and non-local potentials. I got a bit lost with what sounded like technicalities (cut offs, next to next to next leading order), yet it was still possible for me to keep track to where the talk was going until we reached the results.
When the results of the NNNNMNNLO calculations showed up, we saw again how 3 body interactions are there to help us describe nuclear structure of semi light isotopes (Jason Holt's earlier talk), and their effect in the equation of state (EOS) of nuclear matter. Achim can calculate the problem until nuclear matter density, and afterwards he asked his nephew to finish painting the picture.... But the nephew had fever that day, so he had to use polytrops. From these emerged constrained in the EOS that resulted in a neutron star radius of about 12 km +/- a couple of km. The curves shoot straight up from this point in the mass-radius diagram, so the NS mass basically is whatever it wants to be (that's your task astronomer!). He mentioned the results agree nicely with recent constrains from observations (a completely different method) published by another bright young mind, A. Steiner and collaborators (arxiv). Should be fun to watch how the NS community digests these constraints.
My big question at the end was why calculations stop at nuclear density. It seems you have to give the drawing to your nephew right when things take a turn in the mass-radius diagram!
* I had stayed up making the last figure for my talk, which I decided to migrated to the "extra slide section" on the morning!
Contrast that to the instructions we received from the organizers as you might find in the PASI webpage: make a presentation at the Advanced Undergraduate level, and spend like 75% of the talk discussing the open questions in the topic. A clear clash with Feynman's ideas! So lets be fair to the speakers in this my first lecture blog (it took only a week!). Most have made the effort to keep talks at the students level; at least for the first few slides. There were of course a few who couldn't resist and showed off their results right from the start, even though I think we're not the most receptive audience for that kind of stuff... but I digress.
Achim Schwenk talk last Friday started at the (graduate) student level; or so it seemed to my highly under-caffeinated and under-slept experimentalist mind*. The main clear message was: 3-body forces are frontier, they impact the structure and existence of neutron-rich nuclei and neutron-rich matter in astrophysics. Very easy to get it, as it was written explicitly in the second slide.
The highest point of Achim's advanced undergraduateness was a intuitive explanation of three body forces with such mundane objects as the sun, and the moon, and the tides. But we know intuitive explanations can only take us so far in nuclear physics, so soon we were dealing with pion exchange, V_low,k, and non-local potentials. I got a bit lost with what sounded like technicalities (cut offs, next to next to next leading order), yet it was still possible for me to keep track to where the talk was going until we reached the results.
When the results of the NNNNMNNLO calculations showed up, we saw again how 3 body interactions are there to help us describe nuclear structure of semi light isotopes (Jason Holt's earlier talk), and their effect in the equation of state (EOS) of nuclear matter. Achim can calculate the problem until nuclear matter density, and afterwards he asked his nephew to finish painting the picture.... But the nephew had fever that day, so he had to use polytrops. From these emerged constrained in the EOS that resulted in a neutron star radius of about 12 km +/- a couple of km. The curves shoot straight up from this point in the mass-radius diagram, so the NS mass basically is whatever it wants to be (that's your task astronomer!). He mentioned the results agree nicely with recent constrains from observations (a completely different method) published by another bright young mind, A. Steiner and collaborators (arxiv). Should be fun to watch how the NS community digests these constraints.
My big question at the end was why calculations stop at nuclear density. It seems you have to give the drawing to your nephew right when things take a turn in the mass-radius diagram!
* I had stayed up making the last figure for my talk, which I decided to migrated to the "extra slide section" on the morning!
On the origin of heavy species
Ani Aprahamian gave us a nice, quick chronological review of everlasting quest for the answer to the question: what is the world made of?
We quickly see the evolution in this investigation from the ancient Greeks’ four elements (earth, fire, air, and water) to the present Rare Ion Beam facilities, which has allowed us to build the chart of nuclides. There are ~300 stable isotopes known, and lots of unstable ones, which number, some theorist claim could be up to 10 thousand!
OK, so there are way too many different nuclei … now, where are they made? So far we’ve figured out that the lightest elements were created shortly after the Big Bang, other low A elements were synthesized in early stars, and then up to Fe are created in main sequence stars. The creation of heavier elements requires a neutron-rich environment. We’ve come to classify the different nucleosynthesis processes according to the mass range of isotopes they create, for instance the s-process, and the r-process (the location of which is still an open question).
So, it becomes pretty obvious that nuclear physics plays a key role in getting an answer for our question. Nuclear physics experiments aim to learn about the structure of nuclei, the shell closures, the limits of stability, etc. The link between precision astronomical observations and nucleosynthesis models (such as the r-process in supernova, neutrino winds, jets, explosive burning, prompt explosion, GRB) is the nuclear physics! So we do experiments, simulations and nuclear theoretical models. An example to study nucleosynthesis in the r-process: Ani and collaborators ran a network calculation taking Fe as seed nuclei, and considered n-captures competing with beta decays. The process time scale is around 8^4 sec. Does this give the right peaks? We see the accumulation at bottlenecks (nuclei with slow beta-decays). Then, one performs experiments to study such bottlenecks, for instance 78Ni, which is doubly magic. The experiment was performed at the NSCL, and 11 events were recorded, which allowed the first determination of the half-life of this nucleus (Paul Hosmer’s Ph.D. thesis). Another NSCL experiment studied 90Se, 89As, 88,87As (Matt Quinn’s Ph.D. Thesis).
How do we know what to measure next? Ani’s group made a sensitivity study using the FRDM mass model to find out what number gives us the biggest effect on final elemental abundances. They found the most interesting cases to be around closed shells (N=50,and N=82).
Here’s some further reading:
Brian Fields 2002 – Big Bang Nucleosynthesis
Anna Frebel 2006 – Early stars
Grevesse and Noels 1995 – Solar abundance pattern
Olinda/Recife tour
Yesterday we went in a tour to Olinda and Recife and all people that speak portuguese have a lot of fun with the guide when he tried to translate portuguese words in a poor english. Here are the best phrases:
-"arcebisp" (corrupted form of portuguese word "arcebispo", it means archbishop)
-"Let's vamos!" (Instead of let's go)
-"naked woman" (free translation of "Pelada", brazilian's name of a soccer game played with friends everywhere, not at the soccer field)
-"Our lady of Mercy" (Translation word by word of a saint's name: Nossa Senhora da Misericordia. Nossa Senhora = the Blessed Virgin)
I hope now people can understand some phrases of the guide.
-"arcebisp" (corrupted form of portuguese word "arcebispo", it means archbishop)
-"Let's vamos!" (Instead of let's go)
-"naked woman" (free translation of "Pelada", brazilian's name of a soccer game played with friends everywhere, not at the soccer field)
-"Our lady of Mercy" (Translation word by word of a saint's name: Nossa Senhora da Misericordia. Nossa Senhora = the Blessed Virgin)
I hope now people can understand some phrases of the guide.
Sunday, August 8, 2010
The Drinks of Brazil - Juice of Sleeve
Today I am starting a series looking at the many drinks that can be found in Brazil. Today, after a long sweaty day I enjoy a tall cool glass of juice of sleeve. Brazil has many fresh juices from Cashew fruit juice to Mango juice, which this is. The Brazilian word for sleeve is Manga which is also their word for Mango. The hotel staff obviously mistranslated Manga with funny results.
Cold alpha matter
No, this post is not about an insensitive caveman named Alpha proclaiming his importance. Sorry to disappoint. This post is about Serban Misicu's talk on different potential models for the alpha-alpha interaction potential at 0 temperature. The interaction potential models Serban discussed all qualitatively resembled a Lennard-Jones potential; namely they were the Ali-Bodmer, Gogny-D1, Gogny-D1S, and Gogny-D1N potentials. There was also mention of using variational theory of bose liquids to build up from a 2-body force to a 4-body force and beyond. Unfortunately I can't report much more than that about the potentials because I became somewhat bogged down in equations...so I'll skip to the important points: regarding the interaction potential, "there is a significant dependence of saturation on the 2-body potential" and using alpha-cluster expansion and hypernetic chains to model dilute alpha matter provides "consistent results."
You may wonder, does cold alpha matter....matter? Yes! It is present in various places in our universe: clusterization on the surface of nuclei, the Hoyle state in 12C when modeled as a 3-alpha nuclear model, and low density nuclear matter composed of protons, neutrons, and alphas near the neutrino-sphere in core collapse supernovae, to name a few.
If this type of physics is your cup of tea then I strongly urge you to see Serban's slides on the proceedings wiki, as there were equations galore that I can't really describe here. ... that is of course if he actually gets added as a speaker on the wiki page.
You may wonder, does cold alpha matter....matter? Yes! It is present in various places in our universe: clusterization on the surface of nuclei, the Hoyle state in 12C when modeled as a 3-alpha nuclear model, and low density nuclear matter composed of protons, neutrons, and alphas near the neutrino-sphere in core collapse supernovae, to name a few.
If this type of physics is your cup of tea then I strongly urge you to see Serban's slides on the proceedings wiki, as there were equations galore that I can't really describe here. ... that is of course if he actually gets added as a speaker on the wiki page.
Friday, August 6, 2010
TOF mass measurements at NSCL
Alfredo Estrade was my collegue at NSCL where he defended his PhD thesis in TOF mass measurements. In this work, that was a collaboration between MSU and LANL, they measure the new masses of 63V, 63Cr, 66Mn and 74Ni.
Atomic masses play a very important role in nuclear astrophysics, and in particular they can be used to understand processes taking place in the crust of accreting neutron stars, where the extreme density condition drives the composition of nuclear matter towards the neutron drip line. Nuclear masses are needed to determine electron capture transition strengths as well as neutron capture rates, calculated with the Hauser-Feshbach model. Are nuclear reactions a heat source in the crust of neutron stars?
more info: http://th-www.if.uj.edu.pl/acta/vol40/pdf/v40p0695.pdf
I had never seen this version of the world map upsidedown and it makes me think how it would be and what would be different ... would we still be drinking caipirinha every day after the talks or we would be happy with a glass of vodka?
Atomic masses play a very important role in nuclear astrophysics, and in particular they can be used to understand processes taking place in the crust of accreting neutron stars, where the extreme density condition drives the composition of nuclear matter towards the neutron drip line. Nuclear masses are needed to determine electron capture transition strengths as well as neutron capture rates, calculated with the Hauser-Feshbach model. Are nuclear reactions a heat source in the crust of neutron stars?
more info: http://th-www.if.uj.edu.pl/acta/vol40/pdf/v40p0695.pdf
I had never seen this version of the world map upsidedown and it makes me think how it would be and what would be different ... would we still be drinking caipirinha every day after the talks or we would be happy with a glass of vodka?
Evolution of intruder 1f7=2 orbital for upper sd shell nuclei
The seminar was nice because it was about nuclear structure, exactly what I do. There were a lot of information and it was a little difficult to follow everything.
Prof. Maitreyee introduced some experimental results for 35Cl and 30P. One explanation to the experimental positive and negative level energies in these nuclei is modifying the gap between the d3/2 and f7/2. It could be done changing the single particle energies in the spdf effective interaction. She has also shown some others examples in the Sn and Te.
Prof. Maitreyee introduced some experimental results for 35Cl and 30P. One explanation to the experimental positive and negative level energies in these nuclei is modifying the gap between the d3/2 and f7/2. It could be done changing the single particle energies in the spdf effective interaction. She has also shown some others examples in the Sn and Te.
Rare Isotopes Experiments at RIKEN RIBF
I am a big fun of professor's Motobayashi talks and for what I´ve heard from other students this was one of the most awaited talks in the PASI. Motobayashi san showed the status of the new RIBF facility in RIKEN, the first new generation in RI beams.
Energetic heavy-ion beams are converted into intense RI beams via the projectile fragmentation of stable ions or the in-flight fission of uranium ions by the superconducting isotope separator. This upgrade will expand the knownledge of the nuclear chart to presently unreachable region (about 7,000 isotopes predicted but not known) mostly at the neutron rich side.
It is already in operation and the first measurenment was the doppler shifted gamma-ray for excited nuclei in flight. He also showed the production of 127Pd and 128Pd among other 45 new isotopes (Z=25-56) using in flight fission of 238U and the analysis to obtain beta decay half lives is in progress.
more info at: http://www.rarf.riken.jp/Eng/facilities/RIBF.html
Energetic heavy-ion beams are converted into intense RI beams via the projectile fragmentation of stable ions or the in-flight fission of uranium ions by the superconducting isotope separator. This upgrade will expand the knownledge of the nuclear chart to presently unreachable region (about 7,000 isotopes predicted but not known) mostly at the neutron rich side.
It is already in operation and the first measurenment was the doppler shifted gamma-ray for excited nuclei in flight. He also showed the production of 127Pd and 128Pd among other 45 new isotopes (Z=25-56) using in flight fission of 238U and the analysis to obtain beta decay half lives is in progress.
more info at: http://www.rarf.riken.jp/Eng/facilities/RIBF.html
RESOLUT at FSU
Ingo decided that a lot has been said already about 26Al, and he's telling us about the new REsonator SOLenoid with Upscale Transmission (RESOLUT) at Florida State instead. At this facility they use a 9MV tandem accelerator to produce radioactive ion beams at energies around the coulomb barrier, and one reaction of particular interest for them is 25Al(p,g)26Si. After the tandem they have a superconducting linear accelerator followed by superconducting resonators that once were part of Atlas ( at Argonne National Lab). The radioactive beams impinge upon a target gas cell that could be H2, D2, He3, or He4. They use inverse kinematics for their production reactions.
He finally doesn't resist and tells us about his research on 26Al, of astrophysical relevance as we have heard in previous talks. Ingo's group wants to study competition of decay from the isomeric state in 26Al, and for that they study 26Si resonances. They use a surrogate measurement, which has very similar properties to the mechanism of actual interest (for nuclear astro), to study l=0 proton resonances of the p+25Al system.
What about direct measurement of 25Al(p,g)? too difficult, small cross section, high beam quality required. Impossible to do at FSU, could be done at rare ion facilities.
Using HIRA and the (p,d) reaction to study structure near N=50 shell closure
Oh! Bob Tribble! your review talk would have been the perfect intro for this topic! Oh well, here we go: Meredith wants to investigate on nuclear structure near the N=50 shell closure via (p,d) reactions. She ran a 10 day experiment at the NSCL during which her team was able to study several reactions, such as: 84Se(p,d)83Se, 86Kr(p,d)85Kr, 56Ni and 58Ni with (d, 3He) and (p,d). The experiment allowed to extract spectroscopic factors (S) in these nuclei, as well as relevant information for nuclear astrophysics, such as Gamov Teller Strenghts.
Mmmhh, spectroscopic factors, what are those? they tell us what a nucleon is doing, they represent the overlap of two quantum states and let us know about the single-particle properties of valence nucleons ... some discussion sets in now ... It kinda looks to me like people know what S is but they have a hard time explaining it. Oops! A table … what fraction of states is filled out with neutrons? … we want to look at general trends . Shown are N=49 and N=51. Now lets get some data for N=50!
Meredith's experiment at NSCL was completed on May2010, the primary beam was 86Kr @ 150Mev/u, the production target was 9Be, and the S800 spectrograph was used to identify 83Se at the focal plane, charge particle detectors see the deuteron while HIRA measures angle, and energy. The protons for the reaction were provided by a CH2 target, and since trapping mechanism is needed for good angle determination, they used HV foils and MCPs. The analysis of the experiment is in progress, so stay tuned!
The Structure of Rare Isotopes, Taka Otsuka
For me, this was one of the most awaited talks of the conference. I first watched Taka's talk at ENAM in 2008, in Poland. At the time people were digesting his ideas about the tensor force driving major shell structure changes. Not much was mentioned about the role of 3-body forces, not that I recall. Anyhow, I had no idea what he was talking about. I don't think I still do, but when I read that he was coming to PASI and was going to give a talk about his work. Since PASI talks are supposed to be at undergraduate level, I felt that was my chance to finally learn something from this guy. However, I knew it was impossible to review in 45 minutes such a tough subject using undergrad physics. But hey, Taka did a great job!
He started with a very pedagogical intro, showing how to construct many body systems from the basic nuclear forces. He spent some time discussing key features of the bare nn potential. He then moved on to single-particle potential, with our beloved harmonic oscillator potential, added L.S splitting and voilá, there you have the shell model and magic numbers. The universality of magic numbers has been challenged over the years, and he showed us some empirical evidence. As an example, he showed the now famous Tanihata's PRL in halo nuclei, which was published in 1985 - I was 2 years old when this happened, and to me at least it is impressive and scary to see that that this paradigm shift has been happening over my short lifetime.
I think the main message Taka was trying to pass across is that there is large evidence for two major mechanisms that are driving shell evolution a) tensor force, and 3-body force. His "intuitive" picture of the monopole effect of tensor force is starting to sink in my mind, but I have to confess that his discussion on 3-body force was beyond me. I'll definitely need need another couple of years to come to terms with these recent developments.
He started with a very pedagogical intro, showing how to construct many body systems from the basic nuclear forces. He spent some time discussing key features of the bare nn potential. He then moved on to single-particle potential, with our beloved harmonic oscillator potential, added L.S splitting and voilá, there you have the shell model and magic numbers. The universality of magic numbers has been challenged over the years, and he showed us some empirical evidence. As an example, he showed the now famous Tanihata's PRL in halo nuclei, which was published in 1985 - I was 2 years old when this happened, and to me at least it is impressive and scary to see that that this paradigm shift has been happening over my short lifetime.
I think the main message Taka was trying to pass across is that there is large evidence for two major mechanisms that are driving shell evolution a) tensor force, and 3-body force. His "intuitive" picture of the monopole effect of tensor force is starting to sink in my mind, but I have to confess that his discussion on 3-body force was beyond me. I'll definitely need need another couple of years to come to terms with these recent developments.
Studying (alpha,p) reactions important to astrophysical environments
Shigeru Kubono gave a review of (alpha,p) reactions important to explosive stellar environments, touching on sites, observation, some theory, and experimental methods. Though focusing on (alpha,p) reactions, the talk was actually a well composed introduction to the field of the nuclear astrophysics of proton-rich environments.
The proton-rich astrophysical sites covered where classical novae, where a white dwarf star accretes matter from it's main sequence companion; x-ray bursts, where a neutron star accretes matter from it's main sequence companion; and the proton-rich environment in type II supernovae. Observationally we observe the isotopes created in these environments via gamma ray astronomy. P-nuclei which of are particular interest, due to the seeming inability of type II supernovae to produce them in the large quantities they are observed, are 92Mo and 96Ru. At this point the talk turned its focus primarily to alpha-induced reactions with the statement "alpha-induced reactions play an extremely important role for high temperature nucleosynthesis."
A particularly interesting visual tool used to study alpha-induced reactions is the cluster nucleosynthesis diagram (CND). A description without a picture of the diagram would not do it justice, but at the moment I can't get a hold of one. Effectively the diagram shows the energetic favorability of adding alpha particles to nuclei, where simpler systems are at the upper left and more complex systems are at the bottom left of the diagram. An important quality of the diagram is that a lower position on the diagram indicates the particular system is more bound.
After reminding us that nucleosynthesis takes place at very low energy, the talk turned to experimental methods used at RIKEN to study low energy nuclear physics. As we were told, any low energy rare isotope beam (RIB) system consists of the following: 1)Ion Source 2)Accelerator 3)Beam Transport 4)Production Target 5)Separator. RIKEN's low E RIB set-up "CRIB" probes energies less than or equal to 10MeV/u with a beam intensity of 10^3-8 particles per second, a purity of 90-100%, and dE/E between 0.5 and 1$.
We were also given an overview of the thick target method for resonant scattering. This method uses a beam of a single energy, but relies on the fact that the beam will have different energy loss for given events, effectively giving data for a range of energies (clever!). The example target presented was H2 gas and the measurement was made by a Si detector, into which the proton was directed if a resonant state was reached in the beam-target interaction.
Finally an example of why experimental data is crucial, even in the face of sexy theories. I don't remember the reaction rate which was used as an example (a (p,gamma) reaction with something around sodium), but we were shown that the Hauser-Feshbach prediction given by the NACRE collaboration disagreed with data by many orders of magnitude.
The proton-rich astrophysical sites covered where classical novae, where a white dwarf star accretes matter from it's main sequence companion; x-ray bursts, where a neutron star accretes matter from it's main sequence companion; and the proton-rich environment in type II supernovae. Observationally we observe the isotopes created in these environments via gamma ray astronomy. P-nuclei which of are particular interest, due to the seeming inability of type II supernovae to produce them in the large quantities they are observed, are 92Mo and 96Ru. At this point the talk turned its focus primarily to alpha-induced reactions with the statement "alpha-induced reactions play an extremely important role for high temperature nucleosynthesis."
A particularly interesting visual tool used to study alpha-induced reactions is the cluster nucleosynthesis diagram (CND). A description without a picture of the diagram would not do it justice, but at the moment I can't get a hold of one. Effectively the diagram shows the energetic favorability of adding alpha particles to nuclei, where simpler systems are at the upper left and more complex systems are at the bottom left of the diagram. An important quality of the diagram is that a lower position on the diagram indicates the particular system is more bound.
After reminding us that nucleosynthesis takes place at very low energy, the talk turned to experimental methods used at RIKEN to study low energy nuclear physics. As we were told, any low energy rare isotope beam (RIB) system consists of the following: 1)Ion Source 2)Accelerator 3)Beam Transport 4)Production Target 5)Separator. RIKEN's low E RIB set-up "CRIB" probes energies less than or equal to 10MeV/u with a beam intensity of 10^3-8 particles per second, a purity of 90-100%, and dE/E between 0.5 and 1$.
We were also given an overview of the thick target method for resonant scattering. This method uses a beam of a single energy, but relies on the fact that the beam will have different energy loss for given events, effectively giving data for a range of energies (clever!). The example target presented was H2 gas and the measurement was made by a Si detector, into which the proton was directed if a resonant state was reached in the beam-target interaction.
Finally an example of why experimental data is crucial, even in the face of sexy theories. I don't remember the reaction rate which was used as an example (a (p,gamma) reaction with something around sodium), but we were shown that the Hauser-Feshbach prediction given by the NACRE collaboration disagreed with data by many orders of magnitude.
Thursday, August 5, 2010
Who needs charge neutrality?
17.42 Final talk of the day "Effects of Ultra-Strong Electric Fields in Compact Stars" Manuel Malheiros, the man who guided us safely back from downtown Joao Pessoa at 2am last night.
17.52 Looks like he's going to take on some inviolable tenets of neutron star structure - namely the assumption of local charge neutrality. We're going to relax this to global charge neutrality. This should be good.
17.57 We're promised new effects from electric fields in gravity. Enticing....
17.58 Neutron star vital statistics are shown. Electric fields of 10^14 - 10^18 V/cm are the surprise one. Ok, how's this going to work?
17.59 The basics of neutron star physics are (very) rapidly covered: composition, structure, TOV equations (general relativistic hydrostatic equilibrium), the unconstrained nature of the core physics. Half of Shapiro and Teukolsky seems to flash by my eyes in 60 seconds.
18.06 We get to the new stuff. Basically - If neutron stars are gravitationally bound, neutrons are unbound, and COulomb is only a small addition, why can we not have a small amount of charge asymmetry? Back of the envelope calculations show that one can have a charge equal to the square root of the gravitational constant times the mass of the star. This is similar to the charged black hole relation. Intriguing...
18.13 With an E-field, TOV equations are modified - the E-field couples to gravity in general relativity.
18.14 And time is up, so results are going to come thick and fast now...
18.15 Max mass changes with an E-field. More charge, greater max mass, and greater radius - which is intuitive, since the E-force is repulsive. This is the main effect of relaxing local charge neutrality.
18.16 Two minutes after the end of the talk, and we are on to the second section of the talk. I'm not sure I'll be able to keep up.
18.18 The second section is strange stars, specifically the appearance of an electrostatic layer at the stars surface caused by a separation of the quark matter and electrons.
18.25 A question that I was wondering myself is asked - where would the charge, or charge separation, come from? What is the mechanism that produces local charge non-neutrality? Answer - there isn't one! His point is to raise the possibility, rather than postulate the physical mechanism.
18.28 And that's it! Until next time....
17.52 Looks like he's going to take on some inviolable tenets of neutron star structure - namely the assumption of local charge neutrality. We're going to relax this to global charge neutrality. This should be good.
17.57 We're promised new effects from electric fields in gravity. Enticing....
17.58 Neutron star vital statistics are shown. Electric fields of 10^14 - 10^18 V/cm are the surprise one. Ok, how's this going to work?
17.59 The basics of neutron star physics are (very) rapidly covered: composition, structure, TOV equations (general relativistic hydrostatic equilibrium), the unconstrained nature of the core physics. Half of Shapiro and Teukolsky seems to flash by my eyes in 60 seconds.
18.06 We get to the new stuff. Basically - If neutron stars are gravitationally bound, neutrons are unbound, and COulomb is only a small addition, why can we not have a small amount of charge asymmetry? Back of the envelope calculations show that one can have a charge equal to the square root of the gravitational constant times the mass of the star. This is similar to the charged black hole relation. Intriguing...
18.13 With an E-field, TOV equations are modified - the E-field couples to gravity in general relativity.
18.14 And time is up, so results are going to come thick and fast now...
18.15 Max mass changes with an E-field. More charge, greater max mass, and greater radius - which is intuitive, since the E-force is repulsive. This is the main effect of relaxing local charge neutrality.
18.16 Two minutes after the end of the talk, and we are on to the second section of the talk. I'm not sure I'll be able to keep up.
18.18 The second section is strange stars, specifically the appearance of an electrostatic layer at the stars surface caused by a separation of the quark matter and electrons.
18.25 A question that I was wondering myself is asked - where would the charge, or charge separation, come from? What is the mechanism that produces local charge non-neutrality? Answer - there isn't one! His point is to raise the possibility, rather than postulate the physical mechanism.
18.28 And that's it! Until next time....
El triunfo del dragón! ... or, nuclear astrophysics with exotic beams
Nuclear Astrophysics tries to answer one simple question: what is the origin of the elements in the universe?
Alan Chen gave us a general introduction to the topic and then went on to tell us about the distribution of 26Al sources in the milky way.
26Al emits a beta-delayed gamma transition at 1.8 MeV that has been used to characterize stellar evolution in our galaxy (as we heard in a couple other talks as well). 26Al has a short-lived isomer of ~6sec but the decay of its ground state goes to the 1st excited state of 26Mg, (therefore, the gamma lines comes from here).Some important reactions to study in the laboratory are:
26Al(p,g)27Si
25Al(p,g)26Si
What one wants is to determine reaction rates from cross section measurements. In a lot of cases, the reaction rate is dominated by resonant reactions in the compound nucleus, the rate goes as T3/2 (ωγ) exp (-ER/T). Alan described an experiment performed at TRIUMF-ISAC (located in Vancouver, Canada). The goal: determine (p,g) strength of the 188 keV resonance. The technique: inverse kinematics. Experimental details: Beam energy ~ 200 keV/u. 10^9 ions/ sec, Target: silicon carbide (since mass should be comparable to that of the beam). Challenge: build a gas target of H2 without windows, then measure yield of 27Si recoils with DRAGON recoil separator in coincidence with prompt gammas.
The DRAGON recoil separator at TRIMF was designed to perform (p,γ) and (α,γ) reactions relevant for nuclear astrophysics. From the experiment described they measured ωγ= 35 ± 7 μeV!!! Supersensitive measurement!
Future experiment: Direct 25Al(p,g)26Si in order to determine energy levels of 26Si – this could be done indirectly with in-beam gamma ray spectrometry at NSCL p(27Si, 26S)d.
In summary: a sample of completed as well as planned experiments aimed at improving our understanding of stellar explosions were presented. This field benefits from interactions with astronomers and theorists/modelers. Future rare isotope facilities promise a bright future: FAIR, FRIB, RIKEN, TRIUMF, etc.
Leandro's fusion and other new PASI participant arrivals
There are so many new faces in the crowd this evening (and more on the way), and a few missing ones who have flown the coup. It is hard to believe that it is already Thursday. 5 days down. 7 to go.
Leandro's team is so international. Sure, many collaborations are, but his group seems to cover a large number of hemispheres, too! I've heard tons of talks on weakly bound nuclei and how great they are, and here Leandro is talking about reactions with them. Just as you can think of 6Li as a 4He+d molecule, the 10B and 11B are weakly bound nuclei. Break up is bound to happen.
How can you tell experimentally what processes happen before fusion, whether or not these weakly bound nuclei fragment before fusing with 209Bi? Ha- you can't! Oh. Ew. One thing I did like was the span of half-lives he measured, ranging on the order of 100's of ns to hours. Sounds like a planning challenge.
Leandro's team is so international. Sure, many collaborations are, but his group seems to cover a large number of hemispheres, too! I've heard tons of talks on weakly bound nuclei and how great they are, and here Leandro is talking about reactions with them. Just as you can think of 6Li as a 4He+d molecule, the 10B and 11B are weakly bound nuclei. Break up is bound to happen.
How can you tell experimentally what processes happen before fusion, whether or not these weakly bound nuclei fragment before fusing with 209Bi? Ha- you can't! Oh. Ew. One thing I did like was the span of half-lives he measured, ranging on the order of 100's of ns to hours. Sounds like a planning challenge.
Dynamics of many nucleon systems - from nuclear collisions to stellar core collapse
10.59 It's Wolfgang Bauer with Supernova Dynamics via Kinetic Theory.
11.00 I'm still smarting from Wolfgang Bauer's outrageous elbowing of me in yesterday's football game. A clear red card offence.
11.01 Michigan State University is located on a map for us, and the virtues of Michigans summer are extolled.
11.03 Element abundances are shown. A quick recap on the Big Bang nucleosynthesis gives us the relevant timescales and temperatures for nucleon and nuclei freeze-out. At 1s, n/p = 0.22. At 100s, temperature has fallen below 10^9K, nucleons can bond into alpha particles, which vacuum up all the free neutrons.
11.08 Bauer preempts my blog by declaring the one valuable piece of information I am going to get from this talk - He/H = 23% from the Big Bang. That's my work done for today then!
11.09 Ok, I'll press on a little longer and see if I can glean any other information.
11.10 The end point of massive star evolution is run through. Iron core is tipped over the Chandrasekhar limit as the Silicon shell burining deposits more iron. Collapse then ensues.
11.11 The great problem of supernova simulations - they don't explode! (Mostly). Problem is, the realistic simulation of a supernova is an extraordinarily comlicated computational problem. The neutrino flow is especially difficult to include in a self-consistent way and the effects of rotation require multi-dimensional simulation which is obviously much more difficult.
11.16 Limited success with Burrows 2D simulation and Fryers 3D simulation. One big problem is the coupling to Boltzmann equations for neutrino flow which is not done self-consistently.
11.17 Bauer diplomatically avoids stating his opinion of Burrows' acoustic mechanism. Is he talking about his mouth?
11.18 My blog is preempted again by asking the question: where does the 6D phase space transport equation come from? (We're talking nuclear collision simulations now).
11.19 He begins to answer with Many Body Theory in a nutshell. The above equation results from a Wigner transform. So now you know.
11.21 So where does this equation come from?
11.21 + 30 secs. After some details, we're left with 6 differential equations in time for each test particle. But - for a supernova simulation is the number of test particles not a little larger than for heavy ion collisions?
11.23 Ah, yes - this is now addressed. We use 10 million test particles. Each test particle is a moon's worth of baryons. Wow.
11.24 By the way, the great advantage of this method is that it allows a natural (and hence relatively simple) coupling to the neutrino transport equations (also Boltzmann based).
11.29 Some computational details later, we get to some simulations. Woosley and Weaver provide the progenitor core. They have a batch of them in the fridge - they'll send you one if you ask nicely.
11.30 Results from a single processor. BKD EoS is used. A large number of small time steps (10^-5 s) are required because of the interplay of micro- and macroscopic forces.
11.31 I feel some animations coming on. Here we go...
11.34 Lots of dots are moving in front of my eyes. Is this the animation or the Skol from last night?
11.35 We're up to rebound - at a central density of 0.2 nuclear matter density. That's incredibly small (compared to standard modeling)! No uniform nuclear matter in the core at bounce. Very Interesting.
11.38 Summary - new explosion mechanism - neutrino heating and opacity change. The shockwave originates 50km above the neutron star surface. Most interesting to me is the low core density at bounce. I repeat 0.2 TIMES NUCLEAR MATTER DENSITY! (c.f. 2-3 times nuclear matter density as is commonly accepted).
11.45 Excuse the lack of coverage of the questions - I've got my hand up for a question, so typing is inhibited.
11.50 I ask if he has plans to apply his method to an ONeMG core collapse. Answer: No - he has too much on his plate. But he agrees to send me his code so I can do it. That's in writing now - it's binding.
11.52 My voice sounds funny through a microphone.
11.55 Next up is Paulo Gomes with "Fusion enhancement/suppression and irreversibility in reactions induced by weakly bound nuclei". Now say that three times quickly.
11.57 The basic question: in heavy ion collisions, does break up couple to fusion and enhance cross sections or compete with it and suppress them?
11.58 Where is fusion decided - when the Coulomb barrier is breached, or a little way outside? Not sure I understand, given the quantum mechanical nature of barrier penetration.
12.03 Experimental details now.
12.08 The slides are going by apace. I have to admit I'm struggling to keep up. I'm having visions of flan.
12.10 Raabe et al in Nature report that 6He's halo does not enhance fusion probability. The title is misleading - it should read the breakup of 6He's halo.
12.12 At the rick of incurring the wrath of experimentalists, those are some comically large error bars.
12.13 Ok, so we want to compare data on collisions involving stongly and weakly bound projectiles on the same target. Irrelevent differences should be eliminated in the data reduction.
12.16 A long discussion on methods to do this results in a Renormalized Experimental Fusion Function, a Universal Fusion Function and Wong functions. Add them to the Jargon page on the Wiki!
12.19 Finally, by comparing the Renormalized Experimental Fusion Function with the Universal Fusion Function, we get to the breakup effects we're looking for.
12.22 If systems don't follow the expected systematic (which I missed), we are shown three options
1 - Something interesting going on
2 - The experiment is wrong
3 - The calculations are wrong
I think that pretty much covers all of physics.
12.24 Bottom line (for a layman in this field like me) - they've come up with a method of comparing data to theory in examining the collisions involving strongly bound and weakly bound (e.g. halo) nuclei. The conclusions are extensive, and my humble typing skills (I'm up to four fingers now) can's keep up.
12.29 Wolfgang Bauer asks my question from 11.58! I'm so excited I miss the answer.
12.31 So hungry.
12.33 My brain is suddenly being swamped with signals from my stomach. Can't think straight.
12.35 It's lunch! You've been great, and I'll be back later.
11.00 I'm still smarting from Wolfgang Bauer's outrageous elbowing of me in yesterday's football game. A clear red card offence.
11.01 Michigan State University is located on a map for us, and the virtues of Michigans summer are extolled.
11.03 Element abundances are shown. A quick recap on the Big Bang nucleosynthesis gives us the relevant timescales and temperatures for nucleon and nuclei freeze-out. At 1s, n/p = 0.22. At 100s, temperature has fallen below 10^9K, nucleons can bond into alpha particles, which vacuum up all the free neutrons.
11.08 Bauer preempts my blog by declaring the one valuable piece of information I am going to get from this talk - He/H = 23% from the Big Bang. That's my work done for today then!
11.09 Ok, I'll press on a little longer and see if I can glean any other information.
11.10 The end point of massive star evolution is run through. Iron core is tipped over the Chandrasekhar limit as the Silicon shell burining deposits more iron. Collapse then ensues.
11.11 The great problem of supernova simulations - they don't explode! (Mostly). Problem is, the realistic simulation of a supernova is an extraordinarily comlicated computational problem. The neutrino flow is especially difficult to include in a self-consistent way and the effects of rotation require multi-dimensional simulation which is obviously much more difficult.
11.16 Limited success with Burrows 2D simulation and Fryers 3D simulation. One big problem is the coupling to Boltzmann equations for neutrino flow which is not done self-consistently.
11.17 Bauer diplomatically avoids stating his opinion of Burrows' acoustic mechanism. Is he talking about his mouth?
11.18 My blog is preempted again by asking the question: where does the 6D phase space transport equation come from? (We're talking nuclear collision simulations now).
11.19 He begins to answer with Many Body Theory in a nutshell. The above equation results from a Wigner transform. So now you know.
11.21 So where does this equation come from?
11.21 + 30 secs. After some details, we're left with 6 differential equations in time for each test particle. But - for a supernova simulation is the number of test particles not a little larger than for heavy ion collisions?
11.23 Ah, yes - this is now addressed. We use 10 million test particles. Each test particle is a moon's worth of baryons. Wow.
11.24 By the way, the great advantage of this method is that it allows a natural (and hence relatively simple) coupling to the neutrino transport equations (also Boltzmann based).
11.29 Some computational details later, we get to some simulations. Woosley and Weaver provide the progenitor core. They have a batch of them in the fridge - they'll send you one if you ask nicely.
11.30 Results from a single processor. BKD EoS is used. A large number of small time steps (10^-5 s) are required because of the interplay of micro- and macroscopic forces.
11.31 I feel some animations coming on. Here we go...
11.34 Lots of dots are moving in front of my eyes. Is this the animation or the Skol from last night?
11.35 We're up to rebound - at a central density of 0.2 nuclear matter density. That's incredibly small (compared to standard modeling)! No uniform nuclear matter in the core at bounce. Very Interesting.
11.38 Summary - new explosion mechanism - neutrino heating and opacity change. The shockwave originates 50km above the neutron star surface. Most interesting to me is the low core density at bounce. I repeat 0.2 TIMES NUCLEAR MATTER DENSITY! (c.f. 2-3 times nuclear matter density as is commonly accepted).
11.45 Excuse the lack of coverage of the questions - I've got my hand up for a question, so typing is inhibited.
11.50 I ask if he has plans to apply his method to an ONeMG core collapse. Answer: No - he has too much on his plate. But he agrees to send me his code so I can do it. That's in writing now - it's binding.
11.52 My voice sounds funny through a microphone.
11.55 Next up is Paulo Gomes with "Fusion enhancement/suppression and irreversibility in reactions induced by weakly bound nuclei". Now say that three times quickly.
11.57 The basic question: in heavy ion collisions, does break up couple to fusion and enhance cross sections or compete with it and suppress them?
11.58 Where is fusion decided - when the Coulomb barrier is breached, or a little way outside? Not sure I understand, given the quantum mechanical nature of barrier penetration.
12.03 Experimental details now.
12.08 The slides are going by apace. I have to admit I'm struggling to keep up. I'm having visions of flan.
12.10 Raabe et al in Nature report that 6He's halo does not enhance fusion probability. The title is misleading - it should read the breakup of 6He's halo.
12.12 At the rick of incurring the wrath of experimentalists, those are some comically large error bars.
12.13 Ok, so we want to compare data on collisions involving stongly and weakly bound projectiles on the same target. Irrelevent differences should be eliminated in the data reduction.
12.16 A long discussion on methods to do this results in a Renormalized Experimental Fusion Function, a Universal Fusion Function and Wong functions. Add them to the Jargon page on the Wiki!
12.19 Finally, by comparing the Renormalized Experimental Fusion Function with the Universal Fusion Function, we get to the breakup effects we're looking for.
12.22 If systems don't follow the expected systematic (which I missed), we are shown three options
1 - Something interesting going on
2 - The experiment is wrong
3 - The calculations are wrong
I think that pretty much covers all of physics.
12.24 Bottom line (for a layman in this field like me) - they've come up with a method of comparing data to theory in examining the collisions involving strongly bound and weakly bound (e.g. halo) nuclei. The conclusions are extensive, and my humble typing skills (I'm up to four fingers now) can's keep up.
12.29 Wolfgang Bauer asks my question from 11.58! I'm so excited I miss the answer.
12.31 So hungry.
12.33 My brain is suddenly being swamped with signals from my stomach. Can't think straight.
12.35 It's lunch! You've been great, and I'll be back later.
The 22Na puzzle
There is this elusive gamma line at 1275 keV in 22Na, thought to come from novae in detectable amounts ... but it has not been observed! Why?
Are the models wrong?
Are the instruments not sensitive enough? ... this seems to be the most probable answer so far (i.e. a budget - related issue?)
From kiloparsecs to fermi: deciphering the messages of cosmic gamma rays
Roland Diehl got us started today with a review on astronomical observations of gamma rays from rare isotopes.
In the last few decades there has been an impressing advance in astronomical instruments and techniques that have provided us a variety of probes to look into the guts of our galaxy, and beyond. He showed us spectra taken with the INTEGRAL observatory, as well as neat simulations of supernovae (SNe) occurring within a 1 kiloparsec* square.
There are plenty of gamma lines out there and we need to understand their messages. They come from radioactive rare isotopes, which in turn are nucleosynthesis byproducts. By combining experimental nuclear data with observations and theoretical predictions we can infer the gamma ray source dilution time, yields, production mechanism, etc.
For example, 26Al has been used to characterize our galaxy: by calculating how much mass of 26Al is there we can then estimate how many SNe occur per century (about 2). One interesting open question is the correlation between the 511keV line from positron annihilation coming from the beta+ decay of 26Al and its 1809keV line.
Other important gamma emitters and their sources are:
56Ni, 57Ni, 44Ti, 22Na(?) – Interstellar Medium, SNe
44Ti – Inner SNe ejecta
26Al, 60Fe – Cosmic nucleosynthesis, massive stars
*For nuclear physicists: 1 kiloparsec = 30.86×1015 km = 3.086×1034 fermi.
City celebrations - once is enough
Yesterday I went to a square in downtown Joao Pessoa around 10:00 pm. It was a completely rundown place, surrounded by abandoned buildings, a completely crappy place. But it was fun, mainly because I survived! I've met Ani and her sister, zachary meisel, davi chamulak, ana becerill, willliam newton, alfredo estrade, angela bonaccorso, livius trache, manuel malheiros, laercio losano and wife, carlos bertulani and wife, jorge lopez, francesca sammarruca, francisco krmpotic, and others. Apparently the city is getting older. From what I saw yesterday, I confirm that this is true. The music was not good, a kind of distorted rock on top of some reggae. I've hear that david chamulak was very happy to be there!
Wednesday, August 4, 2010
Jogo bonito
The program for our free Wednesday afternoon: intense high quality football (passers by would never have imagined we were a bunch of Physicists!), a splash in the salty sea, and sauna to top it off. Next time there will be some cerveja bem fria.
modeling fission fragments via monte carlo analysis
Perhaps the title of this post would have been a better title for Evandro Andrade's talk, by length standards anyway. But that's a title for another post. Evandro described efforts made with the fission modeling code CRISP to analyze fragment-mass distributions for heavy nuclei. Admittedly it was hard for me to pull much from the talk, but I do not fault Evandro as he only had 10 minutes to speak and there was little to no coverage of his topic in the introductory talks.
What I did learn is that actinide nuclei have 3 fission modes, two which are asymmetric and one which is symmetric. I also learned that Beamer produces mighty fancy presentations and I think I may give it a try in the near future, if I'm feeling ambitious.
What I did learn is that actinide nuclei have 3 fission modes, two which are asymmetric and one which is symmetric. I also learned that Beamer produces mighty fancy presentations and I think I may give it a try in the near future, if I'm feeling ambitious.
nuclear isoscaling
Tuesday afternoon Jorge Lopez from the University of Texas, El Paso gave a talk on nuclear isoscaling. The talk was chock-filled with bouncy animations and methods of studying nuclear isoscaling galore. Alas, I'm still not quite sure what nuclear isoscaling is.
I know that it is strongly related to (or is?) a ratio R, which is equal to the ratio of the number of fragments caused by given heavy ion collisions. The numerator of the ratio is the number of fragments produced in a collision for which there is a high N/Z ratio and the denominator has a low N/Z ratio. Perhaps this R parameter is isoscaling itself? I am not sure as it was simply referred to as R for the remainder of the talk.
Apparently nuclear isoscaling can be studied via molecular dynamics, 3D bond percolation, probabilistic sampling of some sort, and dun dun dunnn...experiment! But note: bouncy animations are apparently a requirement.
My favorite point made in the talk actually emerged incidentally in the Q&A session. Wolfgang Bauer pointed out that the percolation model contained just as much nuclear physics as the Bethe-Wiessaker model (for binding energy), except for Coulomb repulsion.
I know that it is strongly related to (or is?) a ratio R, which is equal to the ratio of the number of fragments caused by given heavy ion collisions. The numerator of the ratio is the number of fragments produced in a collision for which there is a high N/Z ratio and the denominator has a low N/Z ratio. Perhaps this R parameter is isoscaling itself? I am not sure as it was simply referred to as R for the remainder of the talk.
Apparently nuclear isoscaling can be studied via molecular dynamics, 3D bond percolation, probabilistic sampling of some sort, and dun dun dunnn...experiment! But note: bouncy animations are apparently a requirement.
My favorite point made in the talk actually emerged incidentally in the Q&A session. Wolfgang Bauer pointed out that the percolation model contained just as much nuclear physics as the Bethe-Wiessaker model (for binding energy), except for Coulomb repulsion.
Reaction Theory for Pedestrians
Bob Tribble got stranded in Texas and Bertulani is giving a talk about his own work instead. It was an honest account of the problems underpinning nuclear astrophysics from a reactions point of view. I kind of started to understand what the spectroscopic factor means, and how the extrapolations used to determine this value can be dangerous. I also learned from Bertulani where we will go when we die: " to the continuum", and according to him, "The continuum sucks". I have to think about that when I put my head on the pillow later tonight. Anyways, the presentation was nice and accessible for non-experts in the field.
Voce quer uma career fair?
For the local students and young researchers, and foreign too: anyone interested to have a semi-organized chat about work and life as a physicists that side of the equator?
I know this is what coffee breaks are supposed to be for, but during the presentations we've already shown we need a push to break the ice and start asking questions. We just need to increase a bit the overlap of the wave functions of the young local and foreign population, which could be larger as evidenced by the working groups composition (I think the official language of 'nuclear reactions' is Portuguese).
We wouldn't just feed the ugly beast of "brain drain" sociologist and politologos fear so much; we should also explore the dark side of the force. And I'm sure that, after a few days discussing physics by the sunny and salty Atlantic ocean, a few researchers from the northern side are curious about the possibilities of continuing our careers in such a place. It could be a coffee by the pool after lunch, or we could convince Carlos to provide some churrasco in its BBQ some of evenings. State your wish, if any.
I know this is what coffee breaks are supposed to be for, but during the presentations we've already shown we need a push to break the ice and start asking questions. We just need to increase a bit the overlap of the wave functions of the young local and foreign population, which could be larger as evidenced by the working groups composition (I think the official language of 'nuclear reactions' is Portuguese).
We wouldn't just feed the ugly beast of "brain drain" sociologist and politologos fear so much; we should also explore the dark side of the force. And I'm sure that, after a few days discussing physics by the sunny and salty Atlantic ocean, a few researchers from the northern side are curious about the possibilities of continuing our careers in such a place. It could be a coffee by the pool after lunch, or we could convince Carlos to provide some churrasco in its BBQ some of evenings. State your wish, if any.
Tuesday, August 3, 2010
Japanese food in João Pessoa
Hi guys,
I just remember that there is a nice, affordable japanese restaurant not so far from where we are.
It's called Yokan and I strongly recommend :)
I just remember that there is a nice, affordable japanese restaurant not so far from where we are.
It's called Yokan and I strongly recommend :)
More on physics blogs.
Here is appropriate essay from yesterday's NY times, reminding us to blog in moderation: "Rumors in Astrophysics Spread at Light Speed"
Many thanks to our favorite nutritionist for pointing us to this link.
Many thanks to our favorite nutritionist for pointing us to this link.
from nuclei to neutron stars
the second talk in the afternoon started with a philosophical outline reminding the instructions at the PASI web site on how to prepare a talk. What we have done? Why it´s important? What are the open questions? ... I´ve just learn that the EoS is a useful tool. But the question is still open: What´s the relation between the neutron skin and neutron star? I know I have the answer somewhere inside my brain (pause to recall the last talk)
IANM, ChPT, BHF+TBF ... all these abbreviations could go to the jargon index in the wiki page.
I will take a look on her EoS in arXiv: 1002.0146 [nucl-th]. I want to ask how would be possible to measure the neutron skin of 208Pb with an accuracy of 0.05 fm, but I will ask her later. The final slide showed her main point: using consistent microscopic ingredients in the many body theory is the key to predictive power for structure or reaction. ok ... I got it! (thanks David Chamulak)
IANM, ChPT, BHF+TBF ... all these abbreviations could go to the jargon index in the wiki page.
I will take a look on her EoS in arXiv: 1002.0146 [nucl-th]. I want to ask how would be possible to measure the neutron skin of 208Pb with an accuracy of 0.05 fm, but I will ask her later. The final slide showed her main point: using consistent microscopic ingredients in the many body theory is the key to predictive power for structure or reaction. ok ... I got it! (thanks David Chamulak)
From crust to core: Neutron stars are cool!
A beautiful talk just delivered by Jorge Piekarewicz ... we learned that Neutron Stars are a great lab for nuclear matter in which several areas of physics converge: astrophysics, general relativity, atomic, nuclear, particle and condensed matter.
He went on to tell us about symmetry energy, do you remember that important term in the Bethe-Weizsacher mass formula? ... well, you should cause it tells us important things such as which the best proton value for a given A is, and also because it is responsible for the neutron drip line. The symmetry energy is, interestingly, a direct manifestation of the Pauli Exclusion Principle.
Jorge told us about the P-REX experiment that aims to measure the neutron skin in 208Pb, in order to determine the density dependence of the symmetry energy. Here's some more info: http://hallaweb.jlab.org/parity/prex/
I still have a couple questions that I didn't get (dare?) to ask during the discussion session: why did they chose 208Pb for this experiment? ... are there any other nuclei that could be used instead?
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