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

Using the consistent Direct-SemiDirect (DSD) and the improved Preequilibriu m (PEQ) exciton model we analyzed the excitation functions for the neutron radiative capture transitions to the isolated single-particle states in Ce- 141 and Pb-209 in order to study the energy positions of the peaks belongin g to the Brink-Axel Giant Resonances (BA GDR) built on single-particle stat es. The PEQ calculations of gamma 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 ab out 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 rep roduce the available experimental peak energies within about 0.25 MeV. (C) 2001 Elsevier Science B.V. All rights reserved.