A direct measurement of the $\frac{P_M}{P_L}$ electron-capture ratio has been made by means of internal-source scintillation-counter techniques. The ${\mathrm{Cs}}_2$Pt${\mathrm{}\left(\mathrm{CN}\right)\mathrm{}}_4$${\mathrm{H}}_2$O scintillator crystal was synthesized from a Pt compound containing ${}_{}{}^{193}{}_{}{}^{}\mathrm{Pt}$ activity, so that the activity occupied lattice positions in the scintillator. The $\frac{P_M}{P_L}$ capture ratio was found to be 0.386 ± 0.014. From this, the exchange correction for the $\frac{P_M}{P_L}$ capture ratio of Pt could be evaluated to be 1.11 ± 0.04, and from the specific activity of the sample it was possible to re-determine the partial half-life for $L$ capture; the result 73 ± 9 yr corresponds to a $log\mathrm{ft}$ of 7.2±0.1 and a total half-life of 50±9 yr.

• Received 19 February 1971

DOI:https://doi.org/10.1103/PhysRevC.4.601