Threshold Photoneutron Angular Distributions and an M1 Giant Resonance in 208Pb

Abstract
Threshold photoneutron time-of-flight spectra from the 208Pb(γ,n)207Pb reaction have been measured at five angles to the incident photons. Angular distributions obtained for 14 resonances within 850 keV of the 208Pb(γ,n) threshold have led to assignments of M1 strength totalling 67.5 ± 12 eV. The total M1 strength available from spin-flip transitions from the i13/2 neutron shell and the h11/2 proton shell has been calculated to be 100 eV (Weiss). Thus, the data confirm the existence of an M1 giant resonance just above threshold in 208Pb.