THE THERMODYNAMIC PROPERTIES OF ^138,139La NUCLEAR SYSTEMS

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 k_B, 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.