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

Abstract

Two-proton relative momentum (q pp ) and opening angle (θ pp ) distributions from the three-body decay of two excited proton-rich nuclei, namely 23 Al → p + p + 21 Na and 22 Mg → 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 ∼ 20 MeV/c as well as a peak in θ pp around 30 • 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.

Proton-proton correlations in distinguishing the two-proton emission mechanism of Al23 and Mg22

“…This was consistent with the result of no clear observation of diproton emission from the relative momentum and opening angle spectra of 23 Al at any excited states [30]. Generally speaking, a flat protonproton momentum correlation function indicates a very large source size and a very weak two-proton correlation.…”

“…Based on the above results and the q pp and θ pp analysis in Ref. [30], all observables indicate the three-body simultaneous decay mechanism for 22 Mg. Moreover, for the excitations around the 14.044 MeV, T = 2 state a strong diproton-like component was observed.…”

“…The results indicated that the mechanism of two-proton emission from 23 Al was dominately sequential, while that for 22 Mg was mainly three-body simultaneous emission with a strong diprotonlike component at excited states around 14.044 MeV. Based on the previous results [30] and this work, it is possible to distinguish clearly the mechanism of two-proton emission by investigating the proton-proton momentum correlation function, the two-proton relative momentum, and the opening angle distributions. The method presented in this work was applied for the first time to two-proton emitters and was shown to provide new and valuable information on the mechanism of two-proton emission.…”

“…As pointed out in Ref. [30], it is difficult to distinguish between the two-body sequential and three-body simultaneous emission mechanism using the above analysis. In these two mechanisms, the emission time of the two protons is quite different.…”

“…Recently, we have reported the experimental results for kinematically complete measurements of two-proton emissions from two excited proton-rich nuclei, namely, 23 Al → p + p + 21 Na and 22 Mg → p + p + 20 Ne [30]. Based on the analysis of q pp and θ pp distributions of the two emitted protons, a favorable diproton emission component from the excited states around 14.044 MeV of 22 Mg was observed.…”