Abstract
A nucleus is a complex many-body quantum system with quantized energy levels
which correspond to specific wave functions. As the excitation energy (Ex)
increases, the number of quantum states increases exponentially. Hence, their
average spacing decreases with increase in excitation energy. Their average
radiative width increases as Ex increase towards the neutron separation energy,
since it is inversely proportional to the life-time of the energy levels. This
energy region is called the quasi-continuum and the nuclear decay properies in
this energy region are best described using the γ strength function (γSF) and
nuclear level density. According to the detailed-balance principle, the upward
and downward γ strength functions are equivalent if and only if same states
are populated. On the other hand, the generalized Brink-Axel (gBA) hypothesis
suggests that the γSF is independent of the properties of initial and final
states. However, this hypothesis has not been tested thoroughly across the
nuclear chart. Even experimental and theoretical studies that have tested it
are still controversial. Furthermore, the γSF has shown a low energy enhancement,
at energies below 3 MeV, in various nuclei according to the literature.
This structure has the potential to increase r-process reaction rates by up to
more than two orders of magnitude, but its exact occurrence in the nuclear
chart and its physical origin are still open questions. Clarifying this would be
significant for nucleosynthesis. In addition, the description of thermodynamic
properties of nuclei is still one of the challenges of nuclear physics.
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Abstract iii
The main objectives of this project were to i) perform the d(132Xe, p)133Xe inverse
kinematics experiment using the AFRODITE array of iThemba LABS,
ii) analyze these experimental data using the Ratio Method to test the feasibility
of using the Ratio Method in inverse kinematics to probe the shape of
the γSF in the A = 133 mass region of the nuclear chart, iii) search for the low
energy enhancement in the 133Xe nucleus, iv) rigorously test the validity of the
gBA hypothesis, in the 133Xe case, and v) extract the experimental data of the
entropy, nuclear temperature, and specific heat capacity of the 133Xe nucleus,
using the partition function that is obtained from d(132Xe, p)133Xe experimental
data with the Oslo Method, and get more insight into this many-body
system. Both the gBA hypothesis and thermodynamic properties are being
investigated for the first time in this nucleus, and so is the application of the
Ratio Method in inverse kinematics. The results show that it may be feasible
to apply the Ratio Method in inverse kinematics to probe the low energy enhancement,
but it requires higher statistics which may require higher efficiency
γ detection system. It is currently not easy to tell from the γ strength function
ratios whether 133Xe has a low energy enhancement due to the lack of statistics.
However, the γ strength function obtained, in this work and in the literature,
using the Oslo Method shows a plateau at energies below 3 MeV, instead of the
strong low energy enhancement that is predicted by Shell Model calculations.
The results also show, for the first time, that the gBA hypothesis does hold,
within the estimated error bars, in the 133Xe nucleus. Furthermore, the very
first experimental data of the thermodynamic properties of 133Xe show that
this many-body system cools down, even though its energy is rising, which is
the same unique behaviour that is observed in stars and atomic clusters, and
understood using the Bardeen-Cooper-Schrieffer theory.