Radioactive decay of mass-separatedTl192andPb192

Abstract

Mass separated radioactive sources of $^{192}\mathrm{Tl}$ and $^{192}\mathrm{Pb}$ were produced using an isotope separator connected on-line to a cyclotron. Gamma-ray multiscale spectra and electron singles spectra were acquired and $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ and (x-ray)-$\ensuremath{\gamma}$ coincidence measurements made. Half-lives of the ${2}^{\ensuremath{-}}$ and ${7}^{+}$ thallium isomers were determined to be 9.4\ifmmode\pm\else\textpm\fi{}0.2 and 10.8\ifmmode\pm\else\textpm\fi{}0.3 min, respectively. The ${7}^{+}$ isomer decays primarily to a group of negative-parity states built upon a ${5}^{\ensuremath{-}}$ state at 1843.9 keV in $^{192}\mathrm{Hg}$. This structure has been interpreted as a two-neutron band involving ${i}_{\frac{13}{2}}$ and low-$j$ neutrons. The decay of the ${2}^{\ensuremath{-}}$ isomer populates the low-lying positive-parity states in $^{192}\mathrm{Hg}$ in addition to a number of states in the region of 1-2.5 MeV; the properties of the six lowest positive-parity states are compatible with the triaxial-rotor predictions for $\ensuremath{\gamma}\ensuremath{\sim}37\ifmmode^\circ\else\textdegree\fi{}$, a value which also reproduces the structure of bands in adjacent odd-$A$ nuclei. The $^{192}\mathrm{Pb}$ decay to $^{192}\mathrm{Tl}$ is found to have a half-life of 3.5 \ifmmode\pm\else\textpm\fi{} 0.1 min, rather than 2.2 min as reported by previous investigators. Most of the $^{192}\mathrm{Pb}$ decay proceeds to levels at 167.5 and 1195.4 keV, assigned ${\mathrm{I}}^{\ensuremath{\pi}}={1}^{\ensuremath{-}} \mathrm{and} {1}^{+}$, respectively. The systematic variation of the ${1}^{+}$ state in even-$A$ Tl and Au nuclei is discussed in light of the trend of the ${h}_{\frac{11}{2}}$ proton state in odd-$A$ Tl and Au isotopes.RADIOACTIVITY $^{192}\mathrm{Tl}$, $^{192}\mathrm{Tl}^{m}$, $^{192}\mathrm{Pb}$ [from Ta, $W(^{16}\mathrm{O},xn)$, $E=100, 133, 143$ MeV]; mass separated sources; measured ${T}_{\frac{1}{2}}$, ${E}_{\ensuremath{\gamma}}$, ${E}_{\mathrm{ce}}$, ${I}_{\ensuremath{\gamma}}$, ${I}_{\mathrm{ce}}$, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coin, ICC; $^{192}\mathrm{Hg}$, $^{192}\mathrm{Tl}$ deduced levels, $J$, $\ensuremath{\pi}$, multipolarities, $log\mathrm{ft}$.