Beta-Gamma Correlation Measurements onIr192

The $\beta -\gamma$ directional correlation between $\beta$ particles in the 536-keV group and the 605- and 612-keV $\gamma$ rays in the decay of 72-day ${\mathrm{Ir}}^{192}$ has been measured at several $\beta$-ray energies. The measured correlation coefficient $\epsilon \mathrm{}\left(W\right)\mathrm{}$ rises from -0.074±0.015 at 185 keV to -0.096±0.010 at 255 keV and then starts falling; near the end-point energy the anisotropy is found to be very small. The large $\beta -\gamma$ anisotrophy observed conclusively establishes that the parity of ${\mathrm{Ir}}^{192}$ is negative. Attempts have been made to extract information about the relevant matrix-element ratios governing the 536-keV $\beta$ transition. The $\beta -\gamma$ directional correlation between $\beta$ particles in the outer group of 669-keV and the 469-keV $\gamma$ ray $\left(4^{-}\stackrel{\beta }{\to }{4}^{+}\stackrel{\gamma }{\to }{2}^{+}\right)$ has also been measured; it shows nearly isotropic correlation in the $\beta$ energy region 400-650 keV. The $\beta -\gamma$ circular-polarization correlation in the above cascade has also been measured. It is concluded that while large cancellation among the vector-type matrix elements is responsible for the observed energy dependence of the $\beta -\gamma$ anisotropy in the 536-keV $\beta$ group, the outer $\beta$ group of 669 keV apparently satisfies the quasi-allowed approximation. The nature of the 785-keV ($4^{+}$) and 921-keV ($3^{+}$) states in ${\mathrm{Pt}}^{192}$ is discussed in the light of these findings.