Lifetime measurements and evidence for triaxial nuclear shapes in Cs127

Abstract

Rotational bands built on single quasiproton excitations in $^{127}\mathrm{Cs}$ have been investigated using the $^{121}\mathrm{Sb}(^{12}\mathrm{C},\ensuremath{\alpha}2n$) reaction and the ROSPHERE detector array at IFIN-HH, Bucharest. The lifetimes in the yrast negative-parity band based on the proton in ${h}_{11/2}$ orbital have been measured by applying the Doppler-shift attenuation method. The lifetime of the ${7/2}^{+}$ 273-keV state, member of the rotational band associated with the proton ${g}_{7/2}$ orbital, has been determined as $\ensuremath{\tau}$ = 1.22(5) ns by the fast timing technique. The experimental data were compared with the calculations performed using the quasiparticle plus triaxial rotor model and deformation parameters ${\ensuremath{\epsilon}}_{2}$ and $\ensuremath{\gamma}$ have been derived for the positive- and negative-parity structures. Evidence for triaxial nuclear shapes in the states described by the proton ${h}_{11/2}$ orbital was provided by both signature splitting and $B(E2,\mathrm{\ensuremath{\Delta}}J=2)$ transition strengths.