Nuclear structure at the neutron emission threshold and below explored via beta-decays of 82,83Ga and 86As.
Abstract
The work presented in this Ph.D. thesis focuses on the β-decay studies of
neutron-rich nuclei around the N=50 shell closure, with a particular interest in the
population of high energy states around the neutron emission threshold. What is
the structure of these states, are they Pygmy Dipole States (PDR), and how does
beta-decay connect to PDR states are some of the questions that motivated this
study. The research was conducted through two complementary experiments. The
first was performed at the ALTO facility (Accélérateur Linéaire et Tandem d’Orsay)
and aimed at studying β-delayed gamma spectroscopy of 82,83Ge using PARIS
(Photon Array for studies with Radioactive Ion and Stable beams) scintillators and
HPGe detectors. The second experiment, aiming at the study of β-delayed gamma
spectroscopy of 86Se, was carried out at the Ion Guide Isotope Separator On-Line
(IGISOL) facility of the JYFL Accelerator Laboratory at the University of Jyväskylä.
For the latter experiment, the JYFLTRAP Penning trap was used to provide pure
samples of 86As and the β-delayed gamma spectroscopy was performed with
high-resolution germanium detectors.
A detailed analysis of the two experiments is presented. The level schemes of
the β-decay daughters, 82Ge (N=50), 83Ge (N=51), and 86Se (N=52), were updated,
and more than 80 new γ-ray transitions were observed. γ-ray transitions with
energies higher than the neutron separation energy were detected for the first
time in 82Ge. In addition, new gamma-ray transitions following the beta-delayed
neutron emission were observed in both 81Ge and 85Se. The half-lives of 82,83Ga
and 86As were measured as well as the neutron emission probabilities, Pn, of both
83Ga and 86As.
The high-energy states populated in the β-decay of 82Ga lie in a region where
PDR is expected to appear. QRPA and pnQRPA calculations have been performed
for the electric dipole B(E1) and Gamow-Teller strength B(GT) distributions for
82Ge. Calculated B(E1) strength distributions show a low-lying dipole strength
compatible with PDR. The composition of the calculated PDR states can be accessed
in terms of quasi-particle (qp) excitations and neutron and proton transition
densities. Comparing the experimental and calculated B(E1) and B(GT) distributions
and keeping in mind that β-decay can only connect with final states through
particular selection rules, this work discusses the structure of states populated
by beta-decay lying at high energy around the neutron separation energy that
connect directly to the ground or the 2+ state in 82Ge and their eventual dipole
character.
Main Author
Format
Theses
Doctoral thesis
Published
2023
Series
ISBN
978-951-39-9534-8
Publisher
Jyväskylän yliopisto
The permanent address of the publication
https://urn.fi/URN:ISBN:978-951-39-9534-8Use this for linking
ISSN
2489-9003
Language
English
Published in
JYU Dissertations
Copyright© The Author & University of Jyväskylä