USE OF (GAMMA,GAMMA') REACTION FOR STUDYING 141PR LEVELS

Elastic and inelastic scattering of monochromatic photons was used for studying the energy levels of Pr141, the photons being produced by thermal-neutron capture in iron. The resonantly scattered spectrum was measured using Ge(Li) detectors. The energy of the resonance level in Pr141 was found to be 7.632 MeV. Energies and intensities of several γ lines were measured in the region 4.8-7.7 MeV. Assuming these lines to be inelastic transitions de-exciting the resonance level, 19 energy levels were found from the ground state up to 2.8 MeV, 8 of which may be identified with recently reported levels. Angular-distribution measurements of some lines in the scattered spectrum were carried out and the spins of several levels were determined. The parity of the scattering level was measured using a Compton polarimeter and was found to be odd, corresponding to E1 elastically scattered radiation. The total level width of the scattering level was determined using self-absorption and temperature-variation measurements and was found to be Γ=0.133±0.023 eV. The Pr141 levels are discussed in terms of the predictions of the pairing-correlation model. © 1969 The American Physical Society.