Use of the (γ,γ′) Reaction for StudyingPr141Levels

Abstract

Elastic and inelastic scattering of monochromatic photons was used for studying the energy levels of ${}_{}{}^{141}{}_{}{}^{}\mathrm{Pr}$, 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 ${}_{}{}^{141}{}_{}{}^{}\mathrm{Pr}$ was found to be 7.632 MeV. Energies and intensities of several $\gamma$ 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 $E1\mathrm{}$ 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 $\Gamma =0.133\mathrm{}\pm 0.023$ eV. The ${}_{}{}^{141}{}_{}{}^{}\mathrm{Pr}$ levels are discussed in terms of the predictions of the pairing-correlation model.