Electric Monopole Transitions from Excited 0+ States in 156Gd

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Abstract
Internal conversion electron spectra from the decay of 156 Eu were measured at high resolution with an air-core, β-ray spectrometer. The source of 156 Eu was made through the double neutron capture process by irradiating separated 154 Sm with thermal neutrons and was chemically separated. Our data were combined with recent gamma-ray data to deduce conversion coefficients for 47 transitions. The 0 + states at 1049.4, 1168.1 and 1715.2 keV were confirmed. Spins and parities of other states were also assigned or confirmed. A method of analysis for β-band de-excitations is developed with ratios of E2/E0 matrix elements. The β-ground mixing parameter of 156 Gd is obtained to be 0.014, while the β-γ mixing parameter 0.029 for the 2 + β state and 0.005 for the 4 + β state.