Spectroscopy of ${}^{35}$P using the one-proton knockout reaction

Abstract

The structure of ${}^{35}$P was studied with a one-proton knockout reaction at88~MeV/u from a ${}^{36}$S projectile beam at NSCL. The ${\hat{I}}^3$ rays from thedepopulation of excited states in ${}^{35}$P were detected with GRETINA, whilethe ${}^{35}$P nuclei were identified event-by-event in the focal plane of theS800 spectrograph. The level scheme of ${}^{35}$P was deduced up to 7.5 MeV using${\hat{I}}^3-{\hat{I}}^3$ coincidences. The observed levels were attributed to protonremovals from the $sd$-shell and also from the deeply-bound $p\_1/2$ orbital.The orbital angular momentum of each state was derived from the comparisonbetween experimental and calculated shapes of individual (${\hat{I}}^3$-gated)parallel momentum distributions. Despite the use of different reactions andtheir associate models, spectroscopic factors, $C^{2}S$, derived from the${}^{36}$S $(-1p)$ knockout reaction agree with those obtained earlier from${}^{36}$S($d$,\nuc{3}{He}) transfer, if a reduction factor $R\_s$, as deducedfrom inclusive one-nucleon removal cross sections, is applied to the knockout transitions.In addition to the expected proton-hole configurations, other states were observedwith individual cross sections of the order of 0.5~mb. Based on their shiftedparallel momentum distributions, their decay modes to negative parity states,their high excitation energy (around 4.7~MeV) and the fact that they were notobserved in the ($d$,\nuc{3}{He}) reaction, we propose that they may resultfrom a two-step mechanism or a nucleon-exchange reaction with subsequent neutronevaporation. Regardless of the mechanism, that could not yet be clarified, thesestates likely correspond to neutron core excitations in \nuc{35}{P}. Thisnewly-identified pathway, although weak, offers the possibility to selectivelypopulate certain intruder configurations that are otherwise hard to produceand identify.

5 figures, 1 table, accepted for publication in Physical Review C