Dipole strength distribution in Pb-206 for the evaluation of the neutron capture cross section of Pb-205

摘要

The dipole strength distribution of Pb-206 was investigated via a nuclear resonance fluorescence experiment using bremsstrahlung produced with an electron beam at a kinetic energy of 10.5 MeV at the linear accelerator ELBE. We identified 88 states resonantly excited at energies from 3.7 to 8.2 MeV. The analysis of the measured gamma-ray spectra includes the quasicontinuum of levels at high energy. Monte Carlo simulation of gamma-ray cascades were performed to obtain the intensities of inelastic transitions and branching ratios of the ground-state transitions. The extracted photoabsorption cross section shows enhanced dipole strength at the excitation energies around 5.5 and 7 MeV, which may related to a pygmy dipole resonance. The present (gamma, gamma') data combined with (gamma, n) data from the literature were used for confining input parameters of the statistical calculation code CCONE to derive the neutron-capture cross section of the unstable Pb-205 nucleus.