studies in the decay of 131Ba revealing nuclear penetration effects in the 92 keV transition in 131cs

The γ-ray and internal conversion spectra of the decay of 131 Ba to levels in 131 Cs were investigated using a Ge(Li) detector and a double-focussing β-ray spectrometer. Accurate transition energies and internal conversion coefficients were deduced using the internal conversion data of Horen et al . 1 ) in conjunction with the results obtained here. Gamma-gamma and electron-γ directional correlation measurements were performed. Unique spin-parity assignments were obtained for all levels in a compiled level scheme using the deduced conversion coefficients, the results from angular correlation measurements and the deduced log ft values. Nuclear penetration effects were found to be present in the 92 keV transition characterized by λ = 23 −11 +7 .