Mass cartography of the island of inversion points to strong correlation energy:
Analogous to electron shells in chemistry, neutrons and protons occupy similar, exceptionally stable configurations, which are seen as sharp ridges in mass cartography. As the ratio of protons to neutrons changes, this stability can disappear, for example around sodium-31 (31Na). The neighbourhood is difficult to examine due to low production rates and half-lives, too short for a typical Penning-trap mass spectrometer. TITAN, however, routinely measures isotopes with half-lives below 50 ms, or thousands of a second. TITAN's ongoing survey reveals a singularity: The energy, or mass cost, of two neutrons is higher for magnesium-33 (33Mg) than for aluminum-34 (34Al). As reported in Physical Review C (2015) investigating with premier shell-model calculations points to gains in correlation energy as the cause.