Neutron-Deficient Isotopes of Thallium

The activities of the $K$-capturing isotopes of ${\mathrm{Tl}}^{198-202}$ have been investigated. Using 180° beta-ray spectrographs, more than 150 conversion lines have been observed. A new isomer of 1.9-hr half-life has been found and assigned to mass number 198. There are three gamma rays of 282.4, 260.7 (isomeric), and 48.7 kev associated with this activity. No thallium isomers, other than ${\mathrm{Tl}}^{198m}$, or mercury isomers, other than the already known ${\mathrm{Hg}}^{199m}$, were found. The first excited states in ${\mathrm{Hg}}^{200}$ and ${\mathrm{Hg}}^{202}$ were found to be 2+ states. The level schemes of ${\mathrm{Hg}}^{198}$ and ${\mathrm{Hg}}^{200}$ are complex.