Evolution of collectivity along theN=Zline: The84Mo nucleus

Abstract

The reaction ${}^{58}$Ni${(}^{28}$Si,$2n\ensuremath{\gamma})$ at 90 MeV incident energy has been used to populate the $N=Z$ nucleus ${}^{84}$Mo. The GASP array was used together with the ISIS Silicon ball, which allowed a subtraction of the charged particle channels in the \ensuremath{\gamma}-\ensuremath{\gamma} coincidences. The only known transition ${2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+}$ of 443.8 keV in ${}^{84}$Mo has been found in coincidence with a \ensuremath{\gamma} ray of 673.5\ifmmode\pm\else\textpm\fi{}0.4 keV which was assigned as the second ${(4}_{1}^{+}\ensuremath{\rightarrow}{2}_{1}^{+})$ yrast transition. The behavior of the resulting yrast line indicates that ${}^{84}$Mo is a transitional nucleus. The correlation between the excitation energies of the 2${}_{1}^{+}$ and 4${}_{1}^{+}$ levels of the $N=Z$ nuclei reveals a systematic deviation from the average behavior defined by all collective even-even nuclei.