Direct Mapping of Nuclear Shell Effects in the Heaviest Elements

Pinning Down Nuclear Shells The nuclei of heavy atoms are destabilized by proton repulsions, and, conversely, the quantum-mechanical shell effects help to stabilize them. There are theoretical models for predicting the masses of yet-to-be-discovered superheavy elements, based on such shell effects, and these models can be tested by studying the shells of known actinide nuclei. The problem is that current mass values determined from studying radioactive decay products have substantial errors. Minaya Ramirez et al. (p. 1207 , published online 9 August; see the Perspective by Bollen ) were able to collect a sufficient number of nuclei of lawrencium and nobelium isotopes in an ion trap to determine their masses directly by mass spectroscopy. These results will be helpful in predicting the heaviest possible element.