High-spin states in ${}^{191,193}\mathrm{Au}$ and ${}^{192}\mathrm{Pt}$: Evidence for oblate deformation and triaxial shapes

High-spin states of ${}^{191,193}\mathrm{Au}$ and ${}^{192}\mathrm{Pt}$ have been populated in the ${}^{186}\mathrm{W}$(${}^{11}\mathrm{B}$, xn) and ${}^{186}\mathrm{W}$(${}^{11}\mathrm{B}$, p4n) reactions, respectively, at a beam energy of 68 MeV and their γ decay was studied using the YRAST Ball detector array at the Wright Nuclear Structure Laboratory at Yale University. The level scheme of ${}^{193}\mathrm{Au}$ has been extended up to $I^{\pi }=55/2^{+}$. New transitions were observed also in ${}^{191}\mathrm{Au}$ and ${}^{192}\mathrm{Pt}$. Particle-plus-Triaxial-Rotor (PTR) and Total Routhian Surface (TRS) calculations were performed to determine the equilibrium deformations of the Au isotopes. The predictions for oblate deformations in these nuclei are in agreement with the experimental data. Development of nonaxial shapes is discussed within the framework of the PTR model.

Figure 1

Level scheme of ${}^{193}\mathrm{Au}$, as deduced from the ${}^{186}\mathrm{W}$(${}^{11}\mathrm{B}$, 4n) reaction at 68 MeV.

Figure 2

Spectra showing single gates on the 500.2 keV, 454.4 keV, and 436.9 keV transitions, which reveal the γ-rays in ${}^{193}\mathrm{Au}$. Contaminating peaks labeled with * belong to ${}^{192}\mathrm{Au}$, with $♦$ belong to ${}^{191}\mathrm{Au}$, and with • belong to ${}^{192}\mathrm{Pt}$.

Figure 3

Partial level scheme of ${}^{191}\mathrm{Au}$, as deduced from the ${}^{186}\mathrm{W}$(${}^{11}\mathrm{B}$, 6n) reaction at 68 MeV.

Figure 4

Coincidence spectrum gated on the 274.4 keV transition for ${}^{191}\mathrm{Au}$.

Figure 5

Partial level scheme of ${}^{192}\mathrm{Pt}$, as deduced from the ${}^{186}\mathrm{W}$(${}^{11}\mathrm{B}$, p4n) reaction at 68 MeV.

Figure 6

Coincidence spectrum double gated on the 317 keV and 468 keV transitions, which reveals the γ rays in ${}^{192}\mathrm{Pt}$.

Figure 7

(Top) TRS plots for ${}^{192}\mathrm{Pt}$ calculated for (a) $\hslash \omega =0.0$ MeV ($I=0$), which displays a potential minimum for $\gamma =-77.2^{°}$, and (b) $\hslash \omega =0.166$ MeV ($I=14.3$), with a minimum for $\gamma =-69.2^{°}$. (Bottom) TRS plots for ${}^{193}\mathrm{Au}$ calculated for (c) $\hslash \omega =0.127$ MeV ($I=6.2$), which displays a potential minimum for $\gamma =-75.8^{°}$, and (d) $\hslash \omega =0.205$ MeV ($I=18.8$), with a minimum for $\gamma =-72.6^{°}$.

Figure 8

The experimental alignments (top) and Routhians (bottom) for the ground-state bands in ${}^{192}\mathrm{Pt}$ and ${}^{194}\mathrm{Hg}$ and the $\pi h_{11/2}$ band in ${}^{193}\mathrm{Au}$. The alignment for ${}^{193}\mathrm{Au}$ has been reduced by $11/2\hslash$ to simplify comparison with the data from the neighboring nuclides.

Figure 9

Experimental levels in the $\pi h_{9/2}$ bands in the odd-mass ${}^{187,189,191,193}\mathrm{Au}$, compared to PTR calculations.