Electromagnetic Multipolarity of Gamma-Rays and Properties of Neutron-Rich, Deformed Fission Fragments
Eldridge, Jonathan Mark
The E2/M1 mixing ratios have been measured for transitions from states in the one phonon gamma-vibrational bands to states in the ground state bands of of the neutron rich, even-even, deformed isotopes 102,104,106,108Mo, 108,110,112Ru, and 112,114,116Pd. Specifically, the mixing ratios of transitions with Delta J = 0 for J_i even and Delta J=-1 for J_i odd were measured, as these states allow for E2/M1 mixing, including transitions from states as high as 9_gamma^+. At the time of this experiment, Gammasphere had 101 working HPGe detectors, arranged at 64 different angles. A 62 uCi source of 252Cf was placed inside Gammasphere yielding 5.7x10^11 gamma-gamma-gamma and higher coincidence events, including 1.9x10^11 gamma-gamma-gamma-gamma coincidence or higher events. In this experiment, the angular correlations between the transitions from the gamma-bands to the ground bands, and the pure E2 transitions within the ground band were then measured, and used to determine the E2/M1 mixing ratios. The measured mixing ratios have been found to be pure or nearly pure E2, in accordance with theory. Furthermore, from this same 252Cf data set, the structure of 163,164Gd, 156,157,159,164Eu, 89Br, and 155Nd have been explored using gamma-gamma-gamma and gamma-gamma-gamma-gamma coincidences. For 155Nd, 9 new levels and 12 new gamma-rays have been observed, and, based on systematics with 153Nd and 155,157Sm, the spins and parities of the previously known levels were resigned. For 163Gd, 2 new levels and 3 new gamma-rays have been observed, and its structure is found consistent with theoretical calculations and similar levels in the structure of 165Dy. For 156,157,159,164Eu and 89Br, it was determined that our data, combined with deficiencies in the information available in the literature concerning related isotopes, were insufficient to make any concrete determinations. For 164Gd, however, the beta decay of 164Eu was consulted in addition to the above mentioned fission data. These beta-decay data were taken using the Low Energy Radioactive Ion Beam Spectroscopy Station (LeRIBSS) at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory (ORNL). The level scheme of 164Gd has been newly expanded, adding 16 new levels (4 observed in both datasets) and 23 new gamma-rays (3 observed in both datasets). In addition to these, two gamma-rays that had been previously discovered but not placed within the structure of 164Gd, have now been placed within the structure of 164Gd. Furthermore, the half-lives of 164Eu and an isomer within the structure of 164Gd have been measured and found consistent with previous measurements. Comparisons with theory and systematics with other nearby even-even isotopes of Gd has allowed the tentative assignment of quasi particle or collective behavior to most of the newly identified states.