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The investigation of thermodynamic properties of nuclei as a function of excitation energy is one of the challenges in nuclear physics. In this work, we have, for the first time, extracted the entropy, entropy excess, nuclear temperature, and heat capacity of the 138,139La nuclei as a function of excitation energy from their experimental nuclear-level densities. We observed that the odd-odd 138La has a higher entropy due to the additional unpaired neutron. In particular, it has an average entropy excess of 2.3 ± 0.5 κB, which corresponds to the 10 times higher nuclear-level density due to the last unpaired neutron in 138La. The nuclear temperature and heat capacity show evidence for the sequential breaking of Cooper nucleon pairs and as a result, we observed approximately constant temperatures of 0.7 ± 0.3 and 0.8 ± 0.2 MeV in the quasi-continuum of 138La and 139La, respectively. [ABSTRACT FROM AUTHOR]

The generalized Brink–Axel (gBA) hypothesis suggests that the γ-ray strength function (γSF) of a nucleus only depends on the γ-ray energy, and not on the properties of the initial and final excitation energy levels between which the nucleus decays. This hypothesis has been tested in various studies and it is still controversial. In this study, the gBA hypothesis was tested in the A = 138 nuclear mass region by rigorously investigating the dependence of the γSF of 138La on both initial and final excitation energies. The results showed that the shape and absolute value of the γSF are independent of the initial and final excitation energy. Therefore, the results of this work are in support of the generalized Brink–Axel hypothesis. [ABSTRACT FROM AUTHOR]