How magic are the magic numbers?: Tracking single-particle levels in sodium-26:
The standard shell model explains tightly bound nuclei in terms of magic numbers associated with large energy gaps between quantum mechanical single-particle levels. These magic numbers are well understood in nearly stable nuclei, but the magic numbers change in nuclei with a large neutron excess. As published in Physics Letters B (2014), a TIGRESS-SHARC experiment measured reactions of radioactive sodium-25 (25Na) beams on targets containing deuterium (one proton, one neutron). In particular, reactions where one neutron was taken out of the deuterium, measured the single-particle wave function composition of 26Na. The results showed that the neutron single-particle levels are already starting to be squeezed together by a complicated feature of the neutron-proton interaction, an effect which ultimately leads to the breakdown of the neutron magic number 20 in the so-called “island of inversion” around magnesium-32 (32Mg).