Odd couple decays

摘要

The decay of proton-rich nuclei by the emission of a single proton has been known about for some time, and is well understood. The latest observation of two-proton emission, however, will provoke some head-scratching. On page 298 of this issue, Mukha and colleagues report the simultaneous emission of two protons from a complex, long-lived state of the silver isotope ~(94)Ag, which has an odd number of protons. This type of radioactive decay is expected only for proton-rich nuclei with an even number of protons - so the observation leaves nuclear physicists with some explaining to do.