High-Energy Gamma-Ray Transitions From MeV Neutron Capture in 206Pb

Gamma-ray spectra from neutron capture in 206Pb (radiogenic lead) in the energy range 1.5 to 8.5 MeV were recorded using time-of-flight techniques. The gamma-ray spectrometer was a Nal(Tl) crystal, 20.8 cm long and 22.6 cm in diameter. The energy variation of the cross-section for high-energy gamma-ray transitions from the capturing state to low-lying states in the residual nucleus was determined. Comparisons with calculations based on semi-direct and direct capture theories show that these processes are not sufficient to explain the magnitude of the cross-section in the region of the giant dipole resonance. (author)