Model calculations of the radiative capture process and the Brink–Axel hypothesis

Abstract

Using the consistent Direct–SemiDirect (DSD) and the improved Preequilibrium (PEQ) exciton model we analyzed the excitation functions for the neutron radiative capture transitions to the isolated single-particle states in 141 Ce and 209 Pb in order to study the energy positions of the peaks belonging to the Brink–Axel Giant Resonances (BA GDR) built on single-particle states. The PEQ calculations of γ transitions to discrete levels have been performed for the first time. The PEQ model peaks appear at energies lower than those of the BA GDRs for about 0.2 MeV for low-spin states, and for about 0.4 MeV for high-spin ones. The DSD model energies are higher than the BA GDR ones for about 0.3 MeV (1 MeV for high-spin states). Both models reproduce the available experimental peak energies within about 0.25 MeV.