Pairing in excited nuclei: a review

Abstract

The present review summarizes the recent studies on the thermodynamic properties of pairing in many-body systems including superconductors, metallic nanosized clusters and/or grains, solid-state materials, focusing on the excited nuclei, that is nuclei at finite temperature and/ or angular momentum formed via heavy-ion fusion, α-induced fusion reactions, or inelastic scattering of light particles on heavy targets. Because of the finiteness of the systems, several interesting effects of pairing such as nonvanishing pairing gap, smoothing of superfluidnormal phase transition, first and second order phase transitions, pairing reentrance, etc, will be discussed in detail. Influences of exact and approximate thermal pairing on some nuclear properties such as temperature-dependent width of the giant dipole resonance, total level density, and radiative strength function of the γ-rays emission will be also analyzed. Finally, the first experimental evidence of the pairing reentrance phenomenon in a 104 Pd nucleus as well as its solid-state counterpart of ferromagnets under strong magnetic field will be presented.

A fully microscopic model of total level density in spherical nuclei

“…Obviously, the neutron pairing gap ∆ N (proton pairing gap is zero because 60 Ni has a proton magic number) calculated within the exact pairing decreases with increasing T and remains finite even at T = 3 MeV, in agreement with many microscopic calculations (see e.g., Ref. [33]). Consequently, one can see an S-shaped heat capacity, which indicates the signature of superfluid-normal phase transition in finite nuclear systems.…”

Role of exact treatment of thermal pairing in radiative strength functions of $^{161-163}$Dy nuclei

“…It is clear to see in this figure that the exact neutron and proton gaps decrease with increasing T and remain finite even at T = 3 MeV. This feature of the EP gap is well-known for finite nuclei [48][49][50]. In addition, the exact neutron gaps of odd 161,163 Dy nuclei [Figs.…”

Normalizing the enhanced generalized superfluid model of nuclear level density

“…These models are thus able to avoid the dominant of prerequisite mathematical forms as those employed in the phenomenological ones. In addition, some microscopic models have even treated the shell, pairing, and deformation effects together with the collective enhancement factors in a natural way [29][30][31]. However, numerical calcu-lations within the microscopic models are normally complicated, and thus minimize their usage.…”