β-delayed proton emission from nuclei near doubly magic ¹⁰⁰Sn

Abstract

The proton-rich region of the nuclear chart surrounding the doubly magic nucleus ¹⁰⁰Sn (N = Z = 50) is of great interest in nuclear structure studies, in particular when examining the limits of proton stability and the location of the proton drip- line. Measurement of the properties of unstable nuclei in this region serves as a direct test of the shell model for exotic isotopes further from stability. To this end, an experiment was carried out at the Radioactive Ion Beam Factory (RIBF) at RIKEN, Japan. Isotopes in this region were produced following fragmentation of a primary ¹²⁴Xe beam (E beam = 345 MeV/u, beam intensity of 120 pnA) impinged on a 9 Be target, to then be separated and identified, and finally guided along the beamline and implanted in the Advanced Implantation Detector Array (AIDA). AIDA is a state-of-the-art silicon detector array which was used in coincidence with the Decay Total Absorption γ-ray Spectrometer (DTAS), a NaI crystal array γ detection system, to measure the decay properties of exotic, short-lived unstable proton-rich nuclei near ¹⁰⁰Sn.

This thesis presents an analysis of data collected with AIDA during this experiment, notably for the first time with proton-rich nuclei. Measurements of the β-delayed proton decay half-lives, branching ratios and energy spectra of 20 nuclei in the region of ¹⁰⁰Sn are presented in this work, the latter of which was measured with significantly increased energy resolution compared to previous studies.

β-delayed proton emission from ¹⁰¹Sn was analysed in depth, and compared to predictions from shell model calculations in the context of identifying the ground- state spin of this nucleus.

The data collected in this experiment also provided an opportunity to characterise the fast-recovery time of AIDA, in the context of identifying very short-lived decay events with half-lives ∼ μs. This characterisation was applied to constrain the half-life of potential proton emission from an isomer in ⁹⁷In, which has not been directly detected in this work or in previous studies.