Electromagnetic properties ofPt194and the question of its triaxiality

Abstract

In a precision Coulomb excitation experiment, particle spectroscopy with $\alpha$ particles, as well as particle-$\gamma$ coincidence techniques involving $\alpha$ and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ beams were employed to investigate the reduced static and transition matrix elements for the low lying collective states in ${}_{}{}^{194}{}_{}{}^{}\mathrm{Pt}$. The $\alpha$ spectroscopy was carried out in the 7.0 to 17.5 MeV range to check for deviations from pure Coulomb excitation. Besides the familiar Coulomb-nuclear interference which sets in at higher energies, the low energy data show a systematic deviation which is attributed to the combined effects of atomic screening and vacuum polarization. Semiclassical and quantum mechanical coupled channel codes were used to analyze the data. Both sets of data were analyzed in terms of the reduced transition matrix elements that connect the $0^{+}$, $2_1^{+}$, $2_2^{+}$, $4_1^{+}$, $4_2^{+}$, and $3^{-}$ excited states. We also report on the spectroscopic quadrupole moment of the $2_2^{+}$, and $4_1^{+}$ states. The results are compared with several models, including the microscopic pairing-plus-quadrupole model of Kumar and Baranger, and the Davydov's phenomenological asymmetric rigid rotor model. These two models predict a soft-$\gamma$, and assume a rigid-$\gamma$ potential energy surface for ${}_{}{}^{194}{}_{}{}^{}\mathrm{Pt}$, respectively. If ${\chi }^2$ values were to be used as a measure of the "goodness of fit" to the available data, the pairing-plus-quadrupole model (${\chi }^2=0.6\mathrm{}$) would then be favored over the asymmetric rigid rotator model (${\chi }^2=3.3\mathrm{}$).