Nuclear structure studies of neutron-rich nuclei produced in the spontaneous fission of 252Cf: triaxiality near A=110; spherical shapes and octupole correlations beyond 132Sn

Abstract

This dissertation was completed by analyzing gamma-gamma-gamma coincidence data of 252Cf obtained with Gammasphere. A few neutron-rich nuclei in three different mass regions have been studied by establishing their level schemes, determining spin-parities of levels and developing theoretical explanations.

High-spin level schemes of 114,115Rh have been built for the first time. The nuclear structures observed in light odd-odd and odd-even Rh isotopes persist in 114Rh and 115Rh, respectively. The signature inversion observed in 114Rh may be caused by triaxiality. The level structure of 115Rh was interpreted in terms of a rigid-triaxial-rotor-plus-quasiparticle model with gamma=28◦.

High-spin states in 134I have been observed for the first time with five levels. Its structure was explained in terms of the shell model. High-spin level schemes of 137I and 139Cs have been extended. Realistic shell-model calculations have been carried out to interpret the structures of 137I and 139Cs, by choosing 132Sn as a closed core. The calculations provide a very satisfactory description for both isotones up to 3.5 MeV. Our results show the power of the shell model for neutron-rich nuclei up toZ = 55 and N = 84.

The g-factor of the 15/2− state in 137Xe has been measured for the first time, in good agreement with a theoretical prediction from the shell model. Spin-parities of several levels in four N = 83 isotones 135Te, 136I, 137Xe, and 138Cs were determined by measuring gamma-gamma angular correlations. Realistic shell-model alculations support our spin-parity assignments and show configuration mixing in these nuclei that is caused by an additional neutron than in the corresponding N = 82 isotopes and increasing proton numbers.

The nuclear structures of 140,142Cs have been re-investigated and evidence found for octupole correlations. The electric dipole moments for 140,142Cs were measured and compared with neighboring nuclei, where a striking decrease in the Cs isotopic chain with increasing neutron numbers is found. This pronounced drop in electric dipole moments may have a similar origin to that in the Ba isotopes at N = 90.