From first to second minimum: Parity-dependent level densities in $^{240,242}$Pu

We calculate the parity-dependent level density ratios for $^{240,242}$Pu across a broad range of quadrupole deformations, from the spherical configuration up to the superdeformed region, explicitly including both the ground-state minimum and the second minimum (fission isomer). The parity-equilibration energy, defined as the excitation energy at which positive- and negative-parity level densities approach equilibrium, is compared between configurations. A significant reduction is observed near the second minimum, indicating a faster equilibration process in this region.

💡 Research Summary

The paper presents a systematic theoretical investigation of parity‑dependent nuclear level densities (NLDs) for the actinide isotopes ^240Pu and ^242Pu, covering a wide range of quadrupole deformations from the spherical ground‑state minimum through the super‑deformed region up to the second minimum (the fission isomer). Using a finite‑temperature superfluid (BCS) formalism, the authors calculate the total level density ρ(N,Z,U)=exp(S)(2π)^{3/2}|D|^{1/2}, where the entropy S and the determinant D are derived from the partition function Z that includes both neutrons and protons. Single‑particle spectra are generated with a Nilsson Hamiltonian for each deformation β_2, and temperature‑dependent pairing gaps Δ_τ are obtained by solving the BCS equations with a smooth phenomenological interpolation (Δ_τ=Δ_τ0/