Theses and Dissertations

Author

Umesh Silwal

Issuing Body

Mississippi State University

Advisor

Winger, Jeffry A.

Committee Member

Dunne, James A.

Committee Member

Dutta, Dipangkar

Committee Member

Crider, Benjamin P.

Committee Member

Koshka, Yaroslav

Date of Degree

1-1-2018

Document Type

Dissertation - Open Access

Abstract

The National Nuclear Data Center (NNDC) contains a compilation of information on the beta decays of Gallium isotopes. In the mass range A = 74 to 77, the Germanium daughters lie close to or at the valley of stability leading us to believe the decays would have been well studied. However, closer inspection indicates significant conflict for placement of gamma rays and energy levels between different measurements, especially for upper-lying states. Detailed beta-decay studies for the 74-77Ga isotopes were performed using a high resolution four clover Hyper-Pure Germanium (HPGe) detector system with two beta scintillators in the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Lab (ORNL) to better understand the structure of the corresponding 74-77Ge daughter nuclei. In our experiments, use of a high-resolution mass separator greatly improved the purity of the samples in comparison to previous measurements. Besides that, the efficiency of the detector system we utilized was much higher than used in previous studies. We also established a method to determine statistically significant gamma gamma coincidence relationships to add reliability to the placement of gamma rays to energy levels and avoid experimental biases. From our analysis, we have established comprehensive decay schemes for all four Germanium nuclei in this study. In most cases, we have extended the energy levels to cover more of the energy window available for beta decay. Our proposed 74Ge decay scheme contains 44 energy levels occupying up to 4.36-MeV with the placement of 99 gamma rays. Similarly, 75Ga decay scheme contains 72 gamma rays with 29 energy levels occupying up to 2.75 MeV. The 76Ga decay scheme has 49 excited states with 100 gamma rays occupying up to 4.81 MeV. And, the 77Ge decay scheme has 68 gamma rays and 34 energy levels occupying up to 3.14 MeV. Based on the expanded level schemes, betaeeding intensity and log(ft) value lower limits were calculated and attempts were made to assign the spin-parity of the observed states. The resulting level schemes were then compared with the Nushellx theoretical predictions.

URI

https://hdl.handle.net/11668/18728

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