The nuclear photoeffect in holmium and erbium

Abstract

The photoneutron yield and photon scattering cross sections have been measured in the giant resonance region for holmium and erbium. Both cross sections were found to be the same within the experimental uncertainties for the two target materials. The absorption cross section integrated to 23 MeV is 3.20±0.48 MeV·b. The intrinsic nuclear quadrupole moment determined from the giant resonance splitting is 7.6±1.1 b. The observed scattering cross sections were large compared to that calculated from the observed absorption cross section by means of the optical theorem and the dispersion relation. The additional contribution to the scattering cross sections results from the optical anisotropy of these nuclei and can be predicted quantitatively from the expression for the scattering by a three-dimensional classical oscillator. A justification for the classical formulation is given. The data also suggest that in the energy region between 10 and 23 MeV at least 80% of the integrated absorption cross section is associated with charge oscillations along the three spatially correlated nuclear axes.