Nuclear Structure Investigations of some Medium-Weight Isotopes

Abstract

This thesis describes the methods and results of investigations made to determine the decay schemes of three short-lived isotopes 112Ag, 114Ag and 116Ag. A total of 76 γ-rays was observed with a Ge(Li) detector in the γ-radiation which follows the β-decay of 112Ag to levels of 112Cd. γ- γ coincidence and angular correlation measurements were made with Ge(Li)-NaI(T1) and NaI(T1)-NaI(T1) systems. A decay scheme consistent with the present data is proposed. Cross sections for the reactions 112Cd(n,p)112Ag and 115In(n,α)112Ag were measured, and the half-life of the 112Ag decay was found to be 3.14 ± 0.01 hr. The decay scheme of 114Ag was studied with Ge(Li) γ-ray detectors and plastic β-ray detectors. 9 of the 11 γ-rays observed in the decay were incorporated into 114Cd level structure previously determined by conversion electron measurements on the 113Cd(n,γ)114Cd reaction. The endpoint energy of the β-decay was determined as 4.90 ± 0.26 MeV; no branching was evident in the β-spectrum. A decay scheme is proposed for which the β-branching was deduced from the measured γ-ray yield and a calculated cross section value for the 114Cd(n,p)114Ag reaction. The 114Ag half-life was determined as 4.52 ± 0.03 sec; a search for a previously reported isomeric state of 114Ag was unsuccessful. Ge(Li) and NaI(T1) γ-ray detectors were used to study the direct and coincidence spectra that result from the decay of 116Ag, the half-life of which was found to be 2.50 ± 0.02 min. 53 γ-rays were observed from this decay. The β-branching to the 17 excited states of 116Cd in the proposed decay scheme was derived from the measured γ-ray yield and a calculated cross section value for the 116Cd(n,p)Ag reaction. Spin and parity assignments for ihe energy levels of 116Cd are made. An investigation of the applicability of two collective models to nuclear structure typical of the Cd nuclei studied demonstrated that one of the models was misleading when applied to vibrational nuclei. A potential function was developed in the other model to extend the investigation to include a study of the transition between extremes of collective motion. This was used to examine the correspondence between nuclear level schemes representative of rotational and vibrational excitations.