α particles in stable nuclei

Nuclear Physics α Decay is a common mode of radioactivity in heavy elements such as uranium that entails the loss of particles comprising two protons and two neutrons. Despite more than a century of study, when and where these α particles form in stable and unstable nuclei alike remains an open question. Tanaka et al. bombarded a series of stable tin isotopes with high-energy protons and detected ejected α particles at an abundance inversely correlated with mass number (see the Perspective by Hen). This observation, relating α particle accumulation to the neutron skin thickness at the nuclear surface, bears on models spanning radioactive decay to neutron star dynamics. Science , this issue p. [260][1]; see also p. [232][2] [1]: /lookup/doi/10.1126/science.abe4688 [2]: /lookup/doi/10.1126/science.abf2427