The ${}_{}{}^{194,196,198}{}_{}{}^{}\mathrm{Pt}(\overrightarrow{t}, \alpha ){}_{}{}^{193,195,197}{}_{}{}^{}\mathrm{Ir}$ reactions have been studied with a 17 MeV polarized triton beam. Based on the measured angular distributions of cross sections and analyzing powers, several new $I^{\pi }$ assignments were made in ${}_{}{}^{195}{}_{}{}^{}\mathrm{Ir}$ and new levels were identified in ${}_{}{}^{197}{}_{}{}^{}\mathrm{Ir}$. The change in the distribution of $d_{\frac{3}{2}}$ spectroscopic strength as a function of neutron number is observed to be quite dramatic. Two large fragments are observed in ${}_{}{}^{193}{}_{}{}^{}\mathrm{Ir}$, all of the $d_{\frac{3}{2}}$ strength is concentrated in the ground state of ${}_{}{}^{197}{}_{}{}^{}\mathrm{Ir}$, and ${}_{}{}^{195}{}_{}{}^{}\mathrm{Ir}$ shows a situation intermediate between these two. The empirical $d_{\frac{3}{2}}$ strength in ${}_{}{}^{193}{}_{}{}^{}\mathrm{Ir}$ is well reproduced by the predictions of the $\mathrm{U}\left(\frac{6}{4}\right)$ supersymmetry proposed for the Os-Ir-Pt nuclei. The change in the $d_{\frac{3}{2}}$ strength as a function of neutron number is well reproduced by a perturbation of this symmetry.

NUCLEAR REACTIONS ${}_{}{}^{194,196,198}{}_{}{}^{}\mathrm{Pt}(\overrightarrow{t}, \alpha )$, $E_t=17\mathrm{}$ MeV, enriched targets; measured $\sigma (E_{\alpha }, \theta )$, $A_y(E_{\alpha }, \theta )$. ${}_{}{}^{193,195,197}{}_{}{}^{}\mathrm{Ir}$ deduced levels, $I$, $\pi$, spectroscopic strengths.

NUCLEAR STRUCTURE Interacting boson fermion model, $\mathrm{U}\left(\frac{6}{4}\right)$ supersymmetry, spin(6) symmetry.

• Received 25 October 1982

DOI:https://doi.org/10.1103/PhysRevC.27.1040