Decay Modes of Exotic Nuclei

This thesis presents advancements in studying exotic nuclei and rare decay modes through particle and γ-ray coincidence spectroscopy. The focus is on two experimental setups. First, complementing Compex Ge-detector modules with anti-Compton shields. Second, enhancing the Gammasphere-Microball setup at Argonne National Laboratory (ANL) with pixelated silicon detectors. These upgrades enable deeper insights into the structure and behavior of exotic nuclear systems through improved detection and analysis of rare decay events.

A bismuth-germanate (BGO) anti-Compton shield (ACS) for five Compex germanium detector modules was designed, built, and tested with two designs implemented to fit various Compex configurations. The ACS increased the peak-to-total performance by 70% for the ¹³⁷Cs 662-keV peak. These Compex detectors, equipped with ACS, are planned for diverse applications, including local environmental sample measurements, future nuclear structure studies at the GSI Helmholtz Centre for Heavy Ion Research, Germany, and the superheavy element research programme at Lawrence Berkeley National Laboratory, USA.

An experimental campaign at ANL in 2020 focused on odd-Z, neutron-deficient nuclei near ⁵⁶Ni. Two highly pixelated double-sided Si-strip detectors were added to the Gammasphere-Microball setup, improving in-beam proton-γ coincidence spectroscopy and enabling in-beam particle tracking for beam-spot position determination. Excited states in ⁶¹Ga were populated via the fusion-evaporation reaction ²⁴Mg(⁴⁰Ca,p2n)⁶¹Ga, leading to the identification of a proton-emitting state at E_x = 2150(34) keV, interpreted as the π g_9/2 single-particle state. This discovery refined shell-model calculations through studying isospin-breaking parameters for the A=61, T_z=± 1/2 mirror nuclei ⁶¹Ga and ⁶¹Zn.

In the same experiment observed deuteron evaporation from ⁵²Fe^*, ⁵⁶Ni^*, and ⁶⁴Ge^*, based on enhanced light-charged particle sensitivity.
A study was conducted for a few evaporation channels comparing relative production rates for deuteron vs. proton-neutron evaporation as a function of angular momentum and excitation energy.