Discovery of Beta-Delayed Two-Proton Radioactivity:Al22

A proton-proton coincidence experiment has shown that, following the superallowed beta decay of the odd-odd, $T_z=-2\mathrm{}$ nuclide, ${}_{}{}^{22}{}_{}{}^{}\mathrm{Al}$, two protons are emitted with a summed energy spectrum (5.636, 4.139 MeV) characteristic of decay to the ground and first excited states of ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, respectively.