Doctoral Dissertations

Date of Award

5-2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Physics

Major Professor

Robert K. Grzywacz

Committee Members

Thomas Papenbrock, Lawrence Heilbronn, Stefan Spanier

Abstract

Decays of Cu isotopes provide a laboratory to study the properties for nearly doubly-magic nuclei with a significant neutron excess which are also relevant for the r-process models. The beta-decay properties of doubly-magic 78Ni (N=50) are imprinted in the neighboring Cu decay, nuclei with a single proton outside the Z=28 core. The investigated isotopes 79,80,81Cu are strong beta-delayed neutron precursors, suggesting that their decay strength distribution lies above neutron separation energies in 79,80,81Zn daughters.

For decay studies, a segmented scintillator YSO (Y2SiO5 : Ce doped) based implantation detector was developed at the University of Tennessee, Knoxville. The detector is compact in structure and offers good spatial and timing resolution, crucial for ion-β correlations and time-of-flight (ToF) based β-delayed neutron emission spectroscopy, respectively. The detector was employed as a part of the BRIKEN neutron counter at the Radioactive Isotope Beam Factory (RIBF) at RIKEN Nishina Center in Japan, aiming to measure one- and two- neutron emission probabilities (P n,2n ). for nuclei around the 78Ni region. Another variant of the detector with a more advanced design was used along with VANDLE (Versatile Array for Neutron Detection at Low Energy) to conduct spectroscopy of β-delayed neutrons in the same region.

Reconstruction of the feeding intensities requires analysis of neutron-gamma cascades, as is suggested by the statistical model. This work reports the first direct measurements of β-decay strength to neutron-unbound states in the decay of 81, 80, 79Cu. The results from the experiment are compared to shell-model calculations with various sets of single-particle energies and residual interactions. Finally, predictions for 78Ni decay are made based on the model best-describing 79Cu.

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