Anomalous α-decay rate of 192Pb

An anomalous behavior has been reported by Hansen et al. for the α-decay rates of neutron-deficient lead isotopes. In particular, the α reduced width of ¹⁹²Pb appears to be large. Their α-branching ratios, however, are based on (electron capture + β⁺) decay strengths deduced from K x-ray intensities. More precise values can be obtained if the (electron capture + β⁺) decay scheme is known. To this end we investigated the decay properties of ¹⁹²Pb with the use of an on-line isotope separator. The nuclide was produced in the ¹⁸⁰W(¹⁶O,4n) reaction. Singles and coincidence γ-ray data as well as singles conversion-electron spectra were accumulated. Also, singles γ-ray, x-ray, and α-particle spectra were taken with the three detectors placed in calibrated geometries. The ¹⁹²Pb α reduced width was found to be lower by a factor of 2 from that of Hansen et al. but nevertheless much larger than one would expect from neighboring α-emitting nuclides. RADIOACTIVITY ¹⁹²Pb measured T₁₂, E_γ, I_γ, I_ce, E_α, I_α, γγ coin; ¹⁹²Tl deduced levels; ¹⁹²Pb deduced α-decay reduced width. Mass separation.