High-spin states and shape change inSr81

High-spin states have been studied in ${}_{}{}^{81}{}_{}{}^{}\mathrm{Sr}$ using the ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}({}_{}{}^{28}{}_{}{}^{}\mathrm{Si},2\mathrm{}\mathrm{pn}\gamma ){}_{}{}^{81}{}_{}{}^{}\mathrm{Sr}$ reaction at laboratory energies of 103.5 and 108 MeV. $\gamma -\gamma$ coincidence and $\gamma$-ray angular distribution measurements were performed. New states were found at 5353 [${\frac{29}{2}}^{+}$], 5999 [${\frac{31}{2}}^{+}$], 6750 [${\frac{33}{2}}^{+}$], 2448 [${\frac{17}{2}}^{-}$], 2906 [(${\frac{19}{2}}^{-}$)], 3495 [(${\frac{21}{2}}^{-}$)], and 3980 [(${\frac{23}{2}}^{-}$)]. A shape change was seen in the yrast band at the ${\frac{29}{2}}^{+}$ state. Below this level, the band exhibits strong signature splitting and predominant $E2\mathrm{}$ decays. Above it lies a band with almost no signature splitting and predominant $M1\mathrm{}$ decays. The yrare negative parity band shows almost no signature splitting and continues smoothly up to spin ${\frac{23}{2}}^{-}$. The moments of inertia of the positive and negative parity bands are almost the same and increase with spin in a roughly parallel fashion.