UNRESOLVED DIPOLE STRENGTH IN SPECTRA OF THE GD-157(GAMMA,GAMMA') REACTION

A recently proposed fluctuation analysis of resonant photon scattering spectra [J. Enders et al., Phys. Rev. Lea. 79, 2010 (1997)] is applie d to the Gd-157(gamma,gamma') reaction. Evidence for unresolved streng th in the experi mental background is found which amounts to a total d ipole excitation strength of Sigma g Gamma(0)(red) = (30(-10)(+6)) meV /MeV3 in the excitation energy range 2.5-4 MeV. Assuming a smooth vari ation of the M1/E1 strength ratio in the neighboring even-mass nuclei, the M1 part can be estimated to be B(M1) = (2.0(-0.7)(+0.4)) mu(N)(2) . This value is close to the expectation of sum rules. We discuss poss ible sources of errors which suggests that the obtained value represen ts a lower limit only.