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Title: Recoil distance Doppler shift lifetime measurements of excited states in 103 Pd and 106,107 Cd
Author: Ashley, Stephen F.
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 2007
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This thesis outlines two Recoil Distance Doppler-Shift (RDDS) experiments to determine the mean-lifetimes of excited states in 103Pd and 106,107 Cd. The first experiment was performed at the Wright Nuclear Structure Laboratory, Yale University (WNSL). This utilised the ESTU Tandem Van de Graaff accelerator, the New Yale Plunger Device (NYPD) and a variety of HpGe detectors to measure the reaction mu rays. Initially, a backed target experiment was undertaken to determine the level schemes of these nuclei. This fusion-evaporation experiment consisted of a 60 MeV 12C beam impinging on a 0.5mg/cm2 98Mo target with a 9mg/cm2 197Au backing. Thereafter, a RDDS experiment consisting of the same beam impinging on a 1.05mg/cm2 98Mo target with a separate 10mg/cm2 197Au 'stopper' at ten separate target-stopper distances of 11mum, 14mum, 18mum, 23mum, 28mum, 41mum, 56mum, 127mum, 330mum and 2008mum was performed. Prom an offline sort of the data, a series of angle versus angle, two dimensional matrices containing correlated prompt gamma-ray energies were created for each separate distances of the RDDS set. Analysis of these data yielded mean lifetimes of 11.4(17) ps, 8.2(6) ps, 0.89(25) ns and 1.7(6) ps for the Ipi=12+, 11-, 9- and 8- states in 106Cd, at excitation energies of 5418 keV, 4324 keV, 3678 keV and 3507 keV respectively. In addition, mean lifetimes of 31.2(44) ps and 31.4(17) ps were obtained for the states in 103Pd (at Ex = 1360 keV) and 107Cd (at Ex = 1262 keV), respectively. Finally, an upper limit of 4.3(6) ps has been deduced for the mean lifetime of the at Ex = 2168 keV in 107Cd. Prom these measurements, an associated beta2 deformation of 0.135(12) and 0.136(20) have been determined for the Ipi=12+ and 11- states in 106Cd, respectively (assuming axial symmetry). The value for the Ipi=12+ state in 106Cd compares well with predictions of Total Routhian Surface (TRS) calculations. The associated beta2 deformation of 0.12(1) for the state in 103Pd also agrees reasonably with TRS calculations. A second RDDS experiment was performed at the Institut fur Kernphysik, Universitat zu Koln. This utilised the Koln FN Tandem Van de Graaff accelerator, the Koln plunger and a selection of HpGe detectors to measure the reaction gamma rays. This experiment consisted of a 43 MeV 13C beam, impinging on a selection of 96Mo targets with a 6mg/cm2 197Au stopper. In total, measurements of gamma rays at twenty three different target-stopper distances were performed. Prom the subsequent analysis, a mean-lifetime of 17.0(9) ps for the Ipi=2+1 state in 106Cd was determined. Assuming axial symmetry, the associated beta2 deformation of this state is 0.13(1) is in agreement with the TRS prediction of 0.14. The value for the static quadrupole moment agrees with Projected Hartree-Pock-Bogoliubov (PHFB) calculations but deviates from the value reported by Raghavan.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available