## Discovery of Mg-40, Al-42, and Al-43

Baumann *et al.* have recently reported the discovery of three new isotopes ^{40}Mg, ^{42}Al, and ^{43}Al. 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 ^{42}Al 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). ^{42}Al 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 ^{43}Al dot is the collection of ^{42}Al events. The ^{43}Al 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

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