Studies of Neutron-rich Nuclei from 252Cf and 238U + 9Be Fission Fragments

Abstract

This dissertation is a compilation of 1) the experiments measuring the energy and coincidences up to four fold with time gates of gamma rays from fragments produced in 252Cf spontaneous fission obtained with Gammasphere and 2) the experiments measuring the energy, gamma-gamma coincidences of gamma rays from fragments with direct identification of mass and Z in 238U+9Be induced fission with VAMOS+EXOGAM in GANIL. Four fold gamma coincidence data have been built. About 20 neutron rich nuclei in a wide mass region from 96Y to 158Sm have been studied by identifying the gamma transitions, establishing level schemes, determining tentative spins and parities and comparing with theoretical calculations.

The new level schemes of 96,100Y have been established. The 96Y level scheme shows some features of spherical shape at low spin. Band structures in 100Y are similar to pairing free ones. Two bands in 100Y may form a pseudo spin doublet.

A new level scheme of 107Nb has been established for the first time. The new band are similar to the neighboring odd A Nb isotopes.

The new level schemes of 118,119Ag have been established. The 118Ag shows larger signature splitting than 114,116Ag, which may be related to principal axis rotation or evolution of gamma value. The 119Ag might have a magnetic rotation band.

The new level schemes of 147,148Ce have been established. An octupole band in 147Ce has been reported. An 1gamma vibrational band and an 1beta vibrational band in 148Ce were established.

The new transitions in 143-153Pr have been identified and new level schemes of 145,147-153Pr have been established. The previous questioned mass assignments of levels in 151-153Pr have been clarified. Assignments of levels in 151,153Pr by our group have been confirmed. Levels assigned to 152Pr by our group have been assigned to 151Pr. Systematics imply increasing deformation with the increasing neutron number in Pr isotopes from 145-153Pr. The 149,151Pr may have octupole bands.

The new level schemes of 156,157Pm have been established. Levels of 156Pm previously assigned by our group have been reassigned to 157Pm. The new band in 157Pm is almost identical to those in 153,155Pm.

A new level scheme of 158Sm has been established. The new band in 158Sm is proposed to be a two proton quasiparticle band. Levels are in good agreement with theoretical calculations.