Baumann et al. have recently reported the discovery of three new isotopes ⁴⁰Mg, ⁴²Al, and ⁴³Al. The discovery is notable for producing an isotope that neither the finite range droplet model (FRDM) nor the Hartree-Fock-Bogoliubov (HFB-8) predicted should be bound.

Of the 3 isotopes, the discovery of ⁴²Al is an unexpected surprise and thusly the most fascinating. As we all know from undergraduate nuclear chemistry the Weizsäcker’s formula contains a pairing term (d) approximately equal to 34*A^-3/4 MeV. The term increases the binding energy for an even number of protons (Z) and neutrons (N), decreases it for an odd Z and N, and of course is zero for an odd atomic number (A). ⁴²Al contains 13-protons and 29-neutrons, lies on the extreme neutron-rich side, and thus was not predicted to exist in a bound state.

Theory can be seen to be in contradiction from experimental data as seen below.

Reprinted by permission from Macmillan Publishers Ltd: Nature 449, 1022 - 1024 (25 Oct 2007).

To the immediate left of the ⁴³Al dot is the collection of ⁴²Al events. The ⁴³Al event had a probability of ~2 x 10^-3 of arising from the Al-42 cluster of events.

The tantalizing conclusion of this work is that the neutron-drip line may reside further than even the next generation nuclear facilities could explore for Z>12.

Link to article: http://dx.doi.org/10.1038/nature06213

Mitch

Staff Bloggers

	Mitch André Garcia: Mitch is a chemist at Berkeley trying to finish his PhD, one day… (read postings)
	Maz Ali: Maz is a chemist/physicist at Berkeley trying to finish his B.Sc., one day…
	Noel Chang: Noel is a chemist at Berkeley trying to finish Mitch’s PhD, one day…

Welcome to the DNCT’s blog experiment exploring new methods in communicating scientific nuclear knowledge. The goal is to have DNCT members discuss interesting nuclear literature, discuss research questions, and participate more actively with each other.

If you are a DNCT member and would like to be a part of the DNCT blogging team please register for an account here: Login and send an email to mitch-at-berkeley-d0t-edu expressing your interest. Other wise feel free to post comments.

To see a list of tutorials on how to become a part of the blogging team, comment on posts, and generally use the DNCT Blog, see the resources page here.

Mitch