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??