We are investigating the decay properties of even-even lead nuclei with $A\le 192$ in an effort to understand their anomalous $\alpha$-decay rates as reported by Hornshöj et al. Our results for ${}_{}{}^{192}{}_{}{}^{}\mathrm{Pb}$ were recently published. In this study ${}_{}{}^{190}{}_{}{}^{}\mathrm{Pb}$, $T_{\frac{1}{2}}=1.2\mathrm{}\pm 0.1$ min, was produced in the ${}_{}{}^{180}{}_{}{}^{}\mathrm{W}({}_{}{}^{16}{}_{}{}^{}\mathrm{O},6n)$ reaction and its decay was investigated with the use of an on-line isotope separator facility. Singles and coincidence $\gamma$-ray and conversion-electron data were accumulated. In addition, singles $\gamma$-ray and $\alpha$-particle spectra were taken with the detectors positioned in calibrated geometries. Twenty-three transitions were identified and placed into a scheme incorporating 16 levels in ${}_{}{}^{190}{}_{}{}^{}\mathrm{Tl}$. With this decay scheme information and the absolute photon and $\alpha$-particle intensities, the ${}_{}{}^{190}{}_{}{}^{}\mathrm{Pb}$ $\alpha$-decay branch was determined to be (9.0 ± 2.0) × ${10}^{-3\mathrm{}}$, a value about four times greater than that reported by Hornshöj et al. Our new results for ${}_{}{}^{190}{}_{}{}^{}\mathrm{Pb}$ and ${}_{}{}^{192}{}_{}{}^{}\mathrm{Pb}$ indicate that the lead $\alpha$-decay reduced widths may show a dependence on neutron number observed for other elements.

RADIOACTIVITY ${}_{}{}^{190}{}_{}{}^{}\mathrm{Pb}$ measured $T_{\frac{1}{2}}$, $E_{\gamma }$, $I_{\gamma }$, $I_{\mathrm{ce}}$, $E_{\alpha }$, $I_{\alpha }$, $\gamma \gamma$, $\mathrm{ce}\gamma$ coin; ${}_{}{}^{190}{}_{}{}^{}\mathrm{Tl}$ deduced levels; ${}_{}{}^{190}{}_{}{}^{}\mathrm{Pb}$ deduced $\alpha$-decay reduced width. Mass separation.

• Received 12 August 1980

DOI:https://doi.org/10.1103/PhysRevC.23.480