Gamma Decay of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mmultiscripts> <mml:mrow> <mml:mi>Sm</mml:mi> </mml:mrow> <mml:mprescripts/> <mml:none/> <mml:mrow> <mml:mn>154</mml:mn> </mml:mrow> </mml:mmultiscripts> </mml:mrow> </mml:math> Isovector Giant Dipole Resonance: Smekal-Raman Scattering as a Novel Probe of Nuclear Ground-State Deformation
J. Kleemann, N. Pietralla, U. Friman-Gayer, J. Isaak, O. Papst, Kristaq Prifti, V. Werner, A. D. Ayangeakaa, T. Beck, G. Colò, M. L. Cortés, S. W. Finch, M. Fulghieri, D. Gribble, K. Ide, Xavier James, R. V. F. Janssens, S. R. Johnson, P. Koseoglou, Krishichayan, D. Savran, W. Tornow
Abstract
γ decays of the isovector giant dipole resonance (IVGDR) of the deformed nucleus ^{154}Sm were measured using 2_{1}^{+}-Smekal-Raman and elastic scattering of linearly polarized, quasimonochromatic photon beams. The two scattering processes were disentangled through their distinct angular distributions. Their branching ratio and cross sections were determined at six excitation energies covering the ^{154}Sm IVGDR. Both agree with the predictions of the geometrical model for the IVGDR and confirm γ decay as an observable sensitive to the structure of the resonance. Consequently, the data place strong constraints on the nuclear shape, including the degree of triaxiality. The derived ^{154}Sm shape parameters β=0.2925(25) and γ=5.0(15)° agree well with other measurements and recent Monte Carlo shell-model calculations.