Radiochemical investigations of nuclear properties. Progress report, 1 October 1974--30 September 1975

Further studies of the structure of nuclei in the A = 180-200 shape transitional region have been performed. The principal project completed during the current year was an extensive in-beam $gamma$-ray investigation of high-spin levels in the nine nuclei $sup 186$Pt to $sup 194$Pt by ($alpha$,xn$gamma$) reactions on enriched Os targets. Acute backbending observed in the positive parity yrast sequences of $sup 188$,$sup 190$,$sup 192$,$sup 194$Pt has been attributed to the intersection of rotation-aligned ($nu$i-$sup 2$/sub 13/2/) and ($pi$h$sup -2$/sub 11/2/) bands with the ground bands. In all four odd-A Pt nuclei, decoupled $nu$i$sup -1$/sub 13/2/ bands and many other low-lying high- spin positive parity levels have been established, and low-spin positive parity levels have been located in complementary decay studies. A model of an i/sub 13/ 2/ neutron hole coupled to a triaxially deformed core has been found to be rather successful in reproducing these complex level spectra. Other topics dealt with include new $mu$s isomers in $sup 187$,$sup 189$,$sup 191$Pt, the decays of $sup 191$Au, /sup 194m/Ir and 1.7 h $sup 186$Ir and the level structure of $sup 191$Au from an $sup 191$Ir(alpha,4n$gamma$) study. (auth