The $\frac{E2\mathrm{}}{M1\mathrm{}}$ multipole mixing ratios $\delta \left(\gamma \right)$ of $\gamma$ transitions in even-even osmium and platinum isotopes have been measured in order to test the predictions of the pairing-plus-quadrupole theory of Kumar and Baranger. The mixing ratios $\delta \left(\gamma \right)$ were determined from directional-correlation measurements on $\gamma$ transitions in ${}_{}{}^{186,188,190}{}_{}{}^{}\mathrm{Os}$ (populated in the decay of ${}_{}{}^{186,188,190}{}_{}{}^{}\mathrm{Ir}$ and in ${}_{}{}^{194,196}{}_{}{}^{}\mathrm{Pt}$ (populated in the decay of ${}_{}{}^{194,196}{}_{}{}^{}\mathrm{Au}$). The radioactive iridium isotopes were produced by $\mathrm{Re}(\alpha ,xn)$ reactions, and the gold isotopes were produced by $\mathrm{Pt}\mathrm{}(d,xn)\mathrm{}$ reactions. The equipment employed for the $\gamma -\gamma$ directional-correlation measurements consisted of two coaxial 30-cc Ge(Li) detectors and appropriate electronic equipment for high-resolution pulse-height analysis and timing analysis. The observed directional correlations were analyzed in terms of the appropriate $\frac{E2\mathrm{}}{M1\mathrm{}}$ mixing ratios, which are defined explicitly. The following results were obtained (predictions of the Kumar-Baranger theory are listed in square brackets): $\delta ({}_{}{}^{186}{}_{}{}^{}\mathrm{Os}, 630 \mathrm{keV})=-\left({10}_{-4\mathrm{}}^{+15\mathrm{}}\right)[-14.7\mathrm{}]\mathrm{}$, $\delta ({}_{}{}^{186}{}_{}{}^{}\mathrm{Os}, 773 \mathrm{keV})=-\left({13}_{-6\mathrm{}}^{+9\mathrm{}}\right)[-13.5\mathrm{}]\mathrm{}$, $\delta ({}_{}{}^{188}{}_{}{}^{}\mathrm{Os}, 478 \mathrm{keV})=-12.3\mathrm{}\pm 2.8 \mathrm{}[-9.5\mathrm{}]\mathrm{}$, $\delta ({}_{}{}^{188}{}_{}{}^{}\mathrm{Os}, 635 \mathrm{keV})=-6.9\mathrm{}\pm 3.2 \mathrm{}[-10.5\mathrm{}]\mathrm{}$, $\delta ({}_{}{}^{190}{}_{}{}^{}\mathrm{Os}, 371 \mathrm{keV})=-8.5\mathrm{}\pm 1.0 \mathrm{}[-7.6\mathrm{}]\mathrm{}$, $\delta ({}_{}{}^{190}{}_{}{}^{}\mathrm{Os}, 569 \mathrm{keV})=-9.0\mathrm{}\pm 1.5 \mathrm{}[-9.9\mathrm{}]\mathrm{}$, $\delta ({}_{}{}^{194}{}_{}{}^{}\mathrm{Pt}, 293 \mathrm{keV})=+14.3\mathrm{}\pm 2.1 \mathrm{}[+19.9\mathrm{}]\mathrm{}$, $\delta ({}_{}{}^{196}{}_{}{}^{}\mathrm{Pt}, 333 \mathrm{keV})=-5.7\mathrm{}\pm 0.3 \mathrm{}[-101.4\mathrm{}]\mathrm{}$. Except for the 333-keV transition in ${}_{}{}^{196}{}_{}{}^{}\mathrm{Pt}$ the agreement of the experimental mixing ratios with the values and signs predicted by the Kumar-Baranger model is excellent.

• Received 18 August 1970

DOI:https://doi.org/10.1103/PhysRevC.3.240