Si 25 β + -decay spectroscopy

Background: $\ensuremath{\beta}$-decay spectroscopy provides valuable information on exotic nuclei and a stringent test for nuclear theories beyond the stability line.Purpose: To search for new $\ensuremath{\beta}$-delayed protons and $\ensuremath{\gamma}$ rays of $^{25}\mathrm{Si}$ to investigate the properties of $^{25}\mathrm{Al}$ excited states.Method: $^{25}\mathrm{Si}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$ decays were measured by using the Gaseous Detector with Germanium Tagging system at the National Superconducting Cyclotron Laboratory. The protons and $\ensuremath{\gamma}$ rays emitted in the decay were detected simultaneously. A Monte Carlo method was used to model the Doppler broadening of $^{24}\mathrm{Mg}\phantom{\rule{4pt}{0ex}}\ensuremath{\gamma}$-ray lines caused by nuclear recoil from proton emission. Shell-model calculations using two newly developed universal sd-shell Hamiltonians were performed.Results: The most precise $^{25}\mathrm{Si}$ half-life to date has been determined. A new proton branch at 724(4) keV and new proton-$\ensuremath{\gamma}$-ray coincidences have been identified. Three $^{24}\mathrm{Mg}\phantom{\rule{4pt}{0ex}}\ensuremath{\gamma}$-ray lines and eight $^{25}\mathrm{Al}\phantom{\rule{4pt}{0ex}}\ensuremath{\gamma}$-ray lines are observed for the first time in $^{25}\mathrm{Si}$ decay. The first measurement of the $^{25}\mathrm{Si}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$-delayed $\ensuremath{\gamma}$-ray intensities through the $^{25}\mathrm{Al}$ unbound states is reported. All the bound states of $^{25}\mathrm{Al}$ are observed to be populated in the $\ensuremath{\beta}$ decay of $^{25}\mathrm{Si}$. Several inconsistencies between the previous measurements have been resolved, and new information on the $^{25}\mathrm{Al}$ level scheme is provided. An enhanced decay scheme has been constructed and compared to the mirror decay of $^{25}\mathrm{Na}$ and the shell-model calculations.Conclusions: The measured excitation energies, $\ensuremath{\gamma}$-ray and proton branchings, log $ft$ values, and Gamow-Teller transition strengths for the states of $^{25}\mathrm{Al}$ populated in the $\ensuremath{\beta}$ decay of $^{25}\mathrm{Si}$ are in good agreement with the shell-model calculations, offering gratifyingly consistent insights into the fine nuclear structure of $^{25}\mathrm{Al}$.