Shape coexistence in ${}_{}{}^{190}{}_{}{}^{}\mathrm{Hg}$

Levels in ${}_{}{}^{190}{}_{}{}^{}\mathrm{Hg}$ were studied by radioactive decay of isotopically separated ${}_{}{}^{190}{}_{}{}^{}\mathrm{Tl}$. A new band was observed with spin parity (energy, keV) of $0^{+}$(1279), $2^{+}$(1571), $4^{+}$(1975), and $6^{+}$(2510). Electric monopole transitions were observed between this band and the ground-state band. Relative B(E2) values for intraband transitions in the new band were found to be ∼200 times those for interband transitions. Systematics of shape coexistence in the light Hg isotopes and their possible relevance to recent observations of superdeformation in these nuclei are discussed.