Structural investigation of neutron-deficient Pt isotopes: the case of 178 Pt

Lifetime measurements with the recoil distance Doppler-shift technique have been performed to determine yrast E 2 transition strengths in 178 Pt. The experimental data are related to those on neighboring Pt isotopes, especially recent data on 180 Pt, and compared to calculations within the interacting boson model and a Hartree-Fock Bogoliubov approach. These models predict prolate deformed ground states in Pt isotopes close to neutron midshell consistent with the experimental findings. Further, evidence was found that the prolate intruder structure observed in neutron-deficient Hg isotopes that is minimum in energy in 182 Hg becomes the ground state configuration in 178 Pt and neighboring 180 Pt with nearly identical transition quadrupole moments. The new data on 178 Pt are further discussed in the context of the systematics along the Pt isotopic chain with respect to a possible sharp shape transition towards a weakly deformed or a quasi-vibrational ground state whereas the prolate structure increases in energy in 174,176 Pt and becomes an intruder configuration similar to, for example, 180,182 Hg.