Measurements of the Prompt and Delayed Radiation from Fission Fragments: Deformation Properties of Neutron Rich Nuclei
Brewer, Nathan Thomas
Experiments measuring the energy and coincidences associated with gamma rays from nuclei produced in fission have been performed. These experiments probed the physics of deformation as infered from nuclear spectroscopy. At LeRIBSS utilizing the Holifield Radioactive Ion Beam Facility (HRIBF) a uranium carbide target was bombarded with protons and induced to fission. These fragments were accelerated to low energy ($approx$ 200 keV) and measured at the Low-energy Radioactive Ion Beam Spectroscopy Station (LeRIBSS). In an additional experiment, prompt gamma rays from the fragments following californium-252 spontaneous fission(SF) were measured in Gammasphere. The coincidence technique was applied throughout these two studies. However, a number of different techniques were employed at LeRIBSS including mass separation, beta ray detection, gamma ray measurement, half-life information via a Moving Tape Collector (MTC), and digital electronic systems. Some different techniques were applied for the large detection array Gammasphere. In this case, techniques were employed including angular correlation measurement, up to four fold coincidences, and half-life information from time gated cubes. Utilizing these techniques several mass regions have been studied. These experiments allowed for the study of nuclei with different deformation properties, namely cadmium (Cd), gadolinium (Gd), barium (Ba), and cerium (Ce). Cadmium nuclei have been thought to be ideal vibrators exhibiting harmonic spacings nearly identical to models. The beta decay of 122Ag and spectroscopy of 122Cd is presented and evidence is given in support of alternative explanations. Gadolinium nuclei are examined in terms of a quadrupole deformed nucleus from the beta decay of europium(Eu) and from SF. In this study of 162-165Gd, many collective level structures are seen and systematics with neighboring nuclei are examined. Barium and cerium nuclei were studied and considered as candidates for quadrupole-octupole deformation in terms of a geometric model for reflection asymmetry and simplex characterized bands (s= +-1/2 or +-1). In the study of 143-146Ba and 148Ce, the most notable advance is the firm assignment for spins and parities in s= -1 bands in two even-even nuclei. There are, however, alternative explanations for these nuclei and our current study informs these new theories.