PhD Thesis Presentation: β and β-delayed neutron decays of the N = 82 isotopes 128-130Cd and 131In studied with GRIFFIN

PhD Candidate

Ryan Dunlop

Abstract

Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei (GRIFFIN) is a new high-efficiency γ-ray spectrometer designed for use in decay spectroscopy experiments with low-energy radioactive ion beams provided by TRIUMF's Isotope Separator and Accelerator (ISAC-I) facility. The high-efficiency GRIFFIN array is comprised of 16 Compton-suppressed large-volume HPGe clovers,and is designed to be used with a suite of ancillary detectors, providing a powerful and versatile tool for studying exotic nuclei.

The structures of N = 82 nuclei below doubly-magic ¹³²Sn are crucial for calculations of the astrophysical r-process as these isotopes form “waiting-points” that play an important role in the formation and shape of the second r-process abundance peak. Many of the most neutron-rich N = 82 nuclei are, however, out of reach to the current generation of radioactive beam facilities and their properties must be calculated. In the past, shell-model calculations for the half-lives of these nuclei have been performed by adjusting the quenching of the Gamow-Teller (GT) operator in order to reproduce the half-life of ¹³⁰Cd [1]. However, the calculated half-lives of the nuclei below ¹³⁰Cd are known to be systematically too large. Recently, separate measurements with EURICA and GRIFFIN reported a shorter half-life for ¹³⁰Cd leading to a re-scaling of the GT quenching by a constant factor for all nuclei in the region, resolving the discrepancy [2,3]. However, the reduced quenching of the GT operator creates a new discrepancy in the calculated half-life of ¹³¹In. The half-life measurements of nuclei in this region are complicated due to the presence of β-decaying isomers with comparable half-lives and large β-n branches, making γ-ray photo-peak gating with a high-resolution, high-efficiency γ-ray spectrometer, an ideal method to measure each of the isomeric half-lives. This talk will provide an overview of the GRIFFIN γ-ray spectrometer at TRIUMF-ISAC. The half-lives of ^128-130Cd and ¹³¹In [4], as well as the spectroscopy of the one and two neutron-hole nuclei ¹³¹Sn and ¹³⁰Sn [4] will then be presented.

Examination Committee 

• Dr. Robert Wickham, Chair
• Dr. Carl Svensson, Advisor
• Dr. Paul Garrett
• Dr. Dennis Muecher
• Dr. Sean Liddick, External Examiner (Michigan State University)

[1] M. Hannawald et al., Nucl. Phys. A 688, 578 (2001).
[2] R. Dunlop et al., Phys. Rev. C 93, 062801(R) (2016).
[3] G. Lorusso et al., Phys. Rev. Lett. 114, 192501 (2015).
[4] R. Dunlop et al., Phys. Rev. C 99, 045805 (2019).