Abstract
The nuclear level density (NLD) and γ-ray strength function (γSF) of 106Cd
have long carried signi cant uncertainties due to missing neutron resonance
data required for Oslo Method normalization. In particular, the Oslo Method
requires normalization of the NLD at the separation energy using the average
neutron resonance spacing (D0), and of the γSF using both D0 and the average
radiative width (Γγ), to determine their slopes and absolute values. However,
for 106Cd, these parameters are not experimentally available, as 105Cd is unstable.
Previous studies therefore relied on systematics to estimate D0 and
Γγ, introducing large uncertainties into the normalization. Consequently, the
NLD and γSF data of 106Cd, along with the 105Cd(n,γ) cross sections essential
for p-process nucleosynthesis, have lacked experimental accuracy and reliability.
This reanalysis directly addresses one of the IAEA Photon Strength
Function (PSF) team's highlighted case studies, thereby providing new experimental
constraints that contribute to global eorts to improve the reliability
of photon strength functions for 106Cd.
In this work, the NLD and γSF of 106Cd were re-extracted from particle-γ
coincidence data measured at the Oslo Cyclotron Laboratory, using the Oslo
Method in conjunction with the Shape Method. The new γSF is found to be
up to a factor of 3 higher than previously reported γSF, and the new NLD
is lower than previously reported NLD. These results were used to compute
the experimentally constrained calculation of the 105Cd(n, γ) cross sections,
iv
Abstract v
reducing uncertainties of the present neutron capture cross sections of 105Cd
previously based on various NLD and γSF theoretical models by a factor of
4-5, which is a signi cant contribution for astrophysical p-process calculations.
Additionally, the generalized Brink-Axel (gBA) hypothesis, widely used as a
foundational assumption in experimental methods for measuring NLD and γSF
in both nuclear structure and astrophysics, was experimentally tested for the
rst time in the 140La nucleus. The results clearly indicated that the shape
and absolute value of the γSF of 140La do not depend on the nuclear excitation
energy. In particular, the γSF was found to be independent of both initial and
nal excitation energies within experimental uncertainties, supporting that the
gBA hypothesis holds in this mass region.
Finally, the rst experimental study of thermodynamic properties such as entropy,
temperature, and heat capacity in 140La was performed. The results
reveal that the entropy increases from about 2.6 kB to 7.5 kB with excitation
energy, consistent with a growing number of accessible states. The temperature
rises and falls below Ex = 2 MeV, indicating melting of the rst nucleon
Cooper pair. Unlike some nuclei reported in the literature, no distinct temperature
oscillations are observed above 2 MeV; instead, the temperature remains
roughly constant at T ≈ 0.8 MeV, suggesting that the additional excitation
energy is primarily consumed by the sequential breaking of multiple Cooper
pairs, rather than raising the temperature. Furthermore, the heat capacity of
140La uctuates between positive and negative values with increasing excitation
energy, indicating alternating warming and cooling phases. Such unusual
behaviour, contrary to everyday experience, has been observed in the literature
for other nuclei as well as in complex systems such as atomic clusters and
stars.