High-spin states in ${}^{84}\mathrm{Rb}$ have been studied by using the ${}^{70}\mathrm{Zn}$(${}^{18}\mathrm{O},p3n)$${}^{84}\mathrm{Rb}$ reaction at beam energy of 75 MeV. The $\gamma$-$\gamma$ coincidence, excitation function, and ratios for directional correlation of oriented states were determined. A new level scheme was established in which the positive- and negative-parity bands have been extended up to ${17}^{+}$ and ${17}^{-}$ with an excitation energy of about 7 MeV. The signature splitting and signature inversion of the positive-parity yrast band were observed. To understand the microscopic origin of the signature inversion in the yrast positive-parity bands of doubly odd Rb nuclei, as an example, we performed calculations using the projected shell model to describe the energy spectra in ${}^{84}\mathrm{Rb}$. It can be seen that the main features are reproduced in the calculations. This analysis shows that the signature splitting, especially its inversion, can be reproduced by varying only the $\gamma$ deformation with increasing spin. To research the deformation of ${}^{84}\mathrm{Rb}$ carefully, we calculate the total Routhian surfaces of positive-parity yrast states by the cranking shell model formalism. In addition, the results of theoretical calculations about the negative-parity yrast band in ${}^{84}\mathrm{Rb}$ with configuration $\pi (p_{3/2},f_{5/2})\otimes \nu g_{9/2}$ are compared with experimental data, and a band diagram calculated for this band is also shown to extract physics from the numerical results.

• Received 7 November 2009

DOI:https://doi.org/10.1103/PhysRevC.82.014306