States of ${}_{}{}^{200}{}_{}{}^{}\mathrm{Tl}$, populated through the ${}_{}{}^{198}{}_{}{}^{}\mathrm{Pt}({}_{}{}^6{}_{}{}^{}\mathrm{Li},4n)$ reaction at $E=30\mathrm{} \mathrm{to} 40$ MeV, were studied using in-beam $\gamma$-ray spectroscopy techniques. An almost completely new level scheme is presented comprising the $\tilde{\pi }{h}_{\frac{9}{2}}\otimes \tilde{\nu }{i}_{\frac{13}{2}}$ two-quasiparticle band which in this case is built on an $I^{\pi }=7^{-}$ isomeric state ($T_{\frac{1}{2}}=4.8\mathrm{}\pm 0.2$ ns) in contrast to $I^{\pi }=8^{-}$ for all the lighter doubly odd Tl isotopes studied up to now. The systematic variation of the odd-even staggering present in these bands offers arguments to support the interpretation that this phenomenon is related to the signature dependence of the Coriolis interaction.

NUCLEAR REACTIONS ${}_{}{}^{198}{}_{}{}^{}\mathrm{Pt}({}_{}{}^6{}_{}{}^{}\mathrm{Li},4n)$, $E=30\mathrm{}-40$ MeV, measured $E_{\gamma }$, $I_{\gamma }$, $\sigma (E_{{}_{}{}^6{}_{}{}^{}\mathrm{Li}},E_{\gamma },{\theta }_{\gamma })\gamma -\gamma$ coin. ${}_{}{}^{200}{}_{}{}^{}\mathrm{Tl}$ deduced levels, $J$, $\pi$, $T_{\frac{1}{2}}°$. Ge(Li) detectors, enriched target.

• Received 3 October 1980

DOI:https://doi.org/10.1103/PhysRevC.23.748