Decay ofTI188and observed shape coexistence in the bands ofHg188

The decay of the isotope ${}_{}{}^{188}{}_{}{}^{}\mathrm{Tl}$ ($T_{\frac{1}{2}}=71\mathrm{}\pm 1$ s) was studied via conversion-electron, gamma, gamma-gamma, and gamma-conversion-electron measurements. Levels of ${}_{}{}^{188}{}_{}{}^{}\mathrm{Hg}$ were deduced. Two bands with quite different deformation were established. One band is built on a near spherical ground state and the other band is built on a well-deformed shape with an excited $0_2^2$ band head at 824.5 keV. The bands cross and coexist above and below the crossing point. Their crossing explains the unusual behavior of the moment of inertia of the yrast cascade.