Lifetime measurements and evidence for triaxial nuclear shapes in 127Cs

Rotational bands built on single quasiproton excitations in Cs-127 have been investigated using the Sb-121(C-12, 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 h11/2 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 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 epsilon(2) and 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, Delta J = 2) transition strengths.