Sub and Near Barrier Fusion Forming ERBIUM-160*

Available from UMI in association with The British Library. The TESSA2 spectrometer at Daresbury Laboratory has been used to study heavy ion fusion reactions forming the ^{160}Er^ * compound nucleus at bombarding energies ranging from well above to well below the Coulomb barrier. The compound nucleus was formed via four different target-projectile combinations in order to investigate the effects on the reactions of the target-projectile mass asymmetry. The combinations ranged from the perfectly mass symmetric system of ^{80}Se + ^{80}Se through to the very mass asymmetric system of ^{16}O + ^{144}Nd. The other two combinations were ^{44}Ca + ^{116}Cd and ^{36}S + ^{124 }Te. The 2n, 3n 4n and 5n evaporation channels were studied and channel selection was made by gating on low lying transitions in the reaction residues of interest. Total fusion cross sections were obtained from discrete lines in the gamma ray energy spectra observed in germanium detectors. The bismuth germanate (BGO) ball of TESSA2 was used to measure fold distributions which are related to gamma ray multiplicity distributions. These are sensitive to the form of the compound nucleus spin distribution 6(1). The relative total fusion cross sections and partial wave cross sections were compared with simple barrier penetration (SBP) and coupled channels (CC) calculations. SBP calculations are unable to reproduce the experimental data. Calculations including the coupling to excited states of the target and/or projectile in the entrance channel can better reproduce the experimental data. Also presented are comparative measurements between systems of different mass asymmetry formed with essentially the same excitation energy and spin on the basis of SBP models. These provide direct, conclusive evidence of the influence of coupled channels avoiding uncertainties such as the conversion of multiplicity into spin. A report on the "Performance of Germanium Detectors Subject to Neutron Fluxes" is presented. Twenty duet and gamma gauge, hyperpure, n-type, gamma-x detectors were studied for about two years, used in the normal, nuclear structure, experimental environment. (Abstract shortened by UMI.).