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Thermodynamic properties of some selected even-even nuclei such as 56Fe, 60Ni, 98Mo, and 116Sn are studied within the Bardeen-Cooper-Schrieffer theory at finite temperature (FTBCS) taking into account pairing correlations. The theory also incorporates the particle-number projection within the Lipkin-Nogami method (FTLN). The level densities are derived based on the statistical theory of the grand-canonical ensemble (GCE). The results obtained are compared with the recent experimental data by Oslo (Norway) group. It is found that pairing correlations have significant effects on nuclear level density, especially at low and intermediate excitation energies. | Communications in Physics, Vol. 22, No. 4 (2012), pp. 297-308 EFFECTS OF THERMODYNAMIC PAIRING ON NUCLEAR LEVEL DENSITY NGUYEN QUANG HUNG Tan Tao University DANG THI DUNG AND TRAN DINH TRONG Institute of Physics, VAST Abstract. Thermodynamic properties of some selected even-even nuclei such as 56 Fe, 60 Ni, 98 Mo, and 116 Sn are studied within the Bardeen-Cooper-Schrieffer theory at finite temperature (FTBCS) taking into account pairing correlations. The theory also incorporates the particle-number projection within the Lipkin-Nogami method (FTLN). The level densities are derived based on the statistical theory of the grand-canonical ensemble (GCE). The results obtained are compared with the recent experimental data by Oslo (Norway) group. It is found that pairing correlations have significant effects on nuclear level density, especially at low and intermediate excitation energies. I. INTRODUCTION Pairing is a common feature in strongly interacting many-body systems ranging from very large ones such as superconductors or neutron stars to very small ones as atomic nuclei or superconducting ultra-small metallic grains [1]. Pairing correlations have significant effects on the physical properties of atomic nuclei such as the binding and excitation energies, collective motions, rotations, level densities, etc. The Bardeen-Cooper-Schrieffer (BCS) theory [2], a theory of superconductivity, has been widely employed to describe the pairing properties of not only infinite but also finite systems such as atomic nuclei (see e.g. Refs. [3, 4]). At finite temperature T , the finite-temperature BCS (FTBCS) theory predicts a pairing gap which decreases with increasing T and collapses at a given critical temperature TC ≈ 0.568∆(0) with ∆(0) being the pairing gap at zero temperature [4]. As the result, the system undergoes a sharp phase transition from superfluid to normal ones (SN phase transition). This prediction is in very good agreement with the experimental measurements in
