In-beam spectroscopy of neutron midshell Cd and Sn nuclei utilizing channel selection

Abstract

This thesis deals with the experimental methods and instrumentation employed in in-beam γ-ray spectroscopy. Before the experiments, the laboratory facilities were established including construction of the new beam line to the γ-cave and development of ancillary devices. Various Ge-detector arrays were installed and modified applicable for in-beam experiments utilizing weak reaction channels. A new charged particle detector array was constructed in conjunction with the DORIS Ge-detector array. Gamma-ray studies of binary products from 84Kr + 116Cd collisions have been carried out. New yrast states in 114Cd and 116Cd as well as an intruder band on top of the second excited 0+ state in 116Cd have been identified. These new data essentially add to the unique systematics of low-lying collective states in even-even Cd isotopes confirming the distinct behaviour of the intruder states. Excited states up to I ≈ 20 in 115Sn and 116Sn, populated via the (18O,αxn) reactions, have been studied using the DORIS Ge-detector array in conjunction with charged particle detectors. In both nuclei, spherical as well as regular, deformed level structures were found. The spherical states are interpreted to arise from pure neutron configurations, while the deformed, intruder bands obviously involve proton 2p-2h excitations across the Z = 50 shell gap.