Speaker
Dr
Hiroshi Watanabe
(RIKEN)
Description
Shape transitional behavior of atomic nuclei has been one of the major subjects explored in both experimental and theoretical nuclear structure physics. Neutron-rich Z ≈ 40, A ≈ 110 nuclei are predicted to exhibit the phase transitions from prolate, via γ-soft, to oblate shapes with increasing number of neutrons. A major aim of the present research is the spectroscopic study of neutron-rich nuclei in this exotic region, populated using in-flight fission of a 238U beam at 345 MeV/nucleon at the RIBF facility.
This presentation focuses on two new results:
(1) A new isomer with a half-life of 150(30) ns has been identified at an excitation energy of 313 keV in 109Nb. The strong hindrances observed for the isomeric-decay transitions are interpreted as being ascribed to a significant difference in shape between the isomeric state and the states to which the isomer decays. The results will be discussed in the context of possible shape coexistence, based on configuration-constrained potential energy surface calculations for possible single-proton orbits.
(2) For 110Mo, spectroscopic information on the low-lying levels of the γ band built on the Kπ = 2+ state at 494 keV has been obtained for the first time. The experimental finding of the Kπ = 2+ state being lower than the yrast 4+ level suggests that axially-asymmetric γ softness is substantially enhanced in 110Mo, which lies in the proximity of the critical point where prolate-oblate shape transitions occur. The systematics of the low-lying levels in even-even A ≈ 110 nuclei will be discussed in comparison with that in the neutron-rich A ≈ 190 region.
Primary author
Dr
Hiroshi Watanabe
(RIKEN)
