Anomalousα-decay rate ofPb192

An anomalous behavior has been reported by Hansen et al. for the $\alpha$-decay rates of neutron-deficient lead isotopes. In particular, the $\alpha$ reduced width of ${}_{}{}^{192}{}_{}{}^{}\mathrm{Pb}$ appears to be large. Their $\alpha$-branching ratios, however, are based on (electron capture + ${\beta }^{+}$) decay strengths deduced from $K$ x-ray intensities. More precise values can be obtained if the (electron capture + ${\beta }^{+}$) decay scheme is known. To this end we investigated the decay properties of ${}_{}{}^{192}{}_{}{}^{}\mathrm{Pb}$ with the use of an on-line isotope separator. The nuclide was produced in the ${}_{}{}^{180}{}_{}{}^{}\mathrm{W}$(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$,$4n$) reaction. Singles and coincidence $\gamma$-ray data as well as singles conversion-electron spectra were accumulated. Also, singles $\gamma$-ray, x-ray, and $\alpha$-particle spectra were taken with the three detectors placed in calibrated geometries. The ${}_{}{}^{192}{}_{}{}^{}\mathrm{Pb}$ $\alpha$ 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 $\alpha$-emitting nuclides.