Different mechanism of two-proton emission from proton-rich nuclei ²³Al and ²²Mg

Abstract

Two-proton relative momentum ($q_{pp}$) and opening angle (${\theta }_{pp}$) distributions from the three-body decay of two excited proton-rich nuclei, namely ${}^{23}\mathrm{Al}\to \mathrm{p}+\mathrm{p}+{}^{21}\mathrm{Na}$ and ${}^{22}\mathrm{Mg}\to \mathrm{p}+\mathrm{p}+{}^{20}\mathrm{Ne}$, have been measured with the projectile fragment separator (RIPS) at the RIKEN RI Beam Factory. An evident peak at $q_{pp}\sim 20\text{ MeV}/c$ as well as a peak in ${\theta }_{pp}$ around 30° are seen in the two-proton break-up channel from a highly-excited ²²Mg. In contrast, such peaks are absent for the ²³Al case. It is concluded that the two-proton emission mechanism of excited ²²Mg is quite different from the ²³Al case, with the former having a favorable diproton emission component at a highly excited state and the latter dominated by the sequential decay process.