Different mechanism of two-proton emission from proton-rich nuclei ${}^{23}$Al and ${}^{22}$Mg

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