Collective excitations in Gd 150

Mean lifetime measurements of low-lying yrast positive- and negative-parity states of Gd 150 have been performed with the ROSPHERE array using the Ce 140 ( C 13 , 3 n ) fusion-evaporation reaction and the recoil distance Doppler shift method. Precise branching ratios have been obtained from a complementary electron capture decay experiment of both the isomer and ground state of Tb 150 . Reduced E 1 , E 2 , and E 3 transition probabilities were extracted and compared with the corresponding observables in the neighboring isotopes and isotones. The experimental data are compared to the predictions of various theoretical models: quasiparticle random phase approximation, time-dependent Hartree-Fock calculations, the quadrupole-octupole collective Hamiltonian, the mean-field mapped interacting boson model, and the triaxial projected shell model. We find that a complete description of both quadrupole and octupole collectivity, from ground and excited states, is currently lacking, and such measurements of transition strengths are crucial for constraining present and future calculations.