Zeitschrift für Physik. A, Hadrons and nuclei vol:342 issue:3 pages:277-282
The a-branching ratios (b)alpha)) of Pb-192, Pb-190, Pb-188 are measured using mass-separated sources. Different experimental set-ups are used - one detector as well as two detector set-ups - thereby detecting the alpha-particles from the parent and/or via alpha-decay formed daughter nuclei, the beta-delayed gamma radiation from the parent and/or via beta-decay formed daughter nuclei and the Tl KX rays from electron capture decay. Values for b(alpha) of 6.2(6) 10(-5) and 4.0(4) 10(-3) were found for Pb-192, Pb-190 respectively. For Pb-198, limits on the b(alpha) values were obtained: 0.03 < b(alpha) < 0.10. A careful analysis of the previously reported b(alpha) values showed that the discrepancies in the b(alpha) values were not due to inadequate correction procedures, as was suggested, but to experimental uncertainties in the efficiency determination of the different detection set-ups and to an unreliable beta-decay scheme for Pb-188. The b(alpha) obtained in this work show that the lead alpha-decay is not faster than the Hg alpha-decay and that there is no need to assume a disappearance of the Z = 82 shell closure halfway between N = 82 and N = 126.