“145Ba β− decay: Excited states and half-lives in neutron-rich 145La”

Background: Neutron-rich nuclei in the A≈140–160 mass region provide valuable information on nuclear structure such as quadrupole- and octupole-shape coexistence and the evolution of the collectivity. These nuclei have also a nuclear engineering interest because they contribute to the total decay heat after a fission burst. The information concerning 145La is very limited. Purpose: The study of low-spin states in 145La will provide a more detailed level scheme and enable the determination of the half-lives of the excited states. Methods: Low-spin excited states in 145La have been investigated from the 145Baβ− decay. The 145Ba nuclei were directly produced by photofission in the ALTO facility or obtained from the β− decay of 145Cs also produced by photofission. Gamma spectroscopy and fast-timing techniques were used. Results: A new level scheme was proposed including 67 excited levels up to about 3 MeV and 164 transitions. Half-lives in the few-nanosecond range were measured for the first excited states. Configurations for levels up to ≈600 keV were discussed.