Doctoral Dissertations

Date of Award

5-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Physics

Major Professor

Robert Grzywacz

Committee Members

Lawrence Heilbronn, Miguel Madurga, Andrew Steiner

Abstract

Beta-delayed neutron emission in very neutron-rich nuclei plays an essential role in nuclear structure and the understanding of the astrophysical r-process. A complete description of this process requires knowledge of both steps, beta decay and neutron emission. A leading theory poses the intermediate daughter nucleus to behave as a compound nucleus. The conditions for beta-delayed neutron emission of 134In are not well described by the assumptions in the neutron pandemonium hypothesis, therein providing a unique case to this process due to the proximity to 132Sn. Single-particle states in 133Sn obvserved after neutron emission have dissimilar shell occupancy compared to neutron-hole states in daughter nucleus states populated in Gamow-Teller transitions. A short experiment observing 134In decay was conducted with the ISOLDE Decay Station. Multiple neutron-emitting states in 134Sn were identified and the results will be compared with statistical model predictions to establish if the assumption of the "compound nucleus" behavior can be valid for 134In beta-delayed neutron emission. The continued development of radioactive ion beam facilities which can create very neutron rich nuclei necessitates detectors with improved neutron energy resolution and neutron selection. Exotic nuclei near the neutron drip line are far from beta decay stability and become more likely to undergo beta delayed neutron emission processes. The Neutron dEtector with Tracking (NEXT) is a high resolution neutron detector designed as a neutron-gamma discriminating-plastic scintillator detector with position sensitive readout. Recent advancements in PSD plastic scintillators as well as position sensitive detectors are the foundation of the compact design of the NEXT detector. A segmented detector prototype has been made from optically separated bars of EJ-276 (Eljen Technology) coupled to a position sensitive PMT and has been shown to have correlated position and timing with monoenergetic neutrons from proof of principle tests.

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