Multiparticle configurations inN=84isotones located at the proton drip line

Abstract

Excited states in the proton-rich $N=84$ isotones ${}_{72}^{156}{\mathrm{Hf}}_{84},\phantom{\rule{0.3em}{0ex}}{}_{73}^{157}{\mathrm{Ta}}_{84}$, and ${}_{74}^{158}{W}_{84}$ were observed using $^{102}\mathrm{Pd}(^{58}\mathrm{Ni},\phantom{\rule{0.3em}{0ex}}\mathit{xp}2n)$ reactions at 270 MeV. \ensuremath{\gamma} rays were detected with the Gammasphere array of Compton-suppressed Ge detectors coupled with the Argonne fragment mass analyzer and were assigned to individual reaction channels using the recoil-decay tagging method. Prompt \ensuremath{\gamma}-ray cascades were associated with the \ensuremath{\alpha} decay of both the ground state and the ${8}^{+}$ isomeric state in $^{156}\mathrm{Hf}$, the ${h}_{11/2}$ state in $^{157}\mathrm{Ta}$, and the ${8}^{+}$ isomeric state in $^{158}\mathrm{W}$. The level schemes constructed for $^{156}\mathrm{Hf},^{157}\mathrm{Ta}$, and $^{158}\mathrm{W}$ are compared with these of lighter $N=84$ isotones and are discussed within the framework of the shell model.