$K$-shell autoionization has been observed in the $\beta$ decay of ${}_{}{}^{203}{}_{}{}^{}\mathrm{Hg}$. The intensity of $\mathrm{Tl}K \mathrm{x}$ rays was measured in coincidence with 279-keV $\gamma$ rays from ${}_{}{}^{203}{}_{}{}^{}\mathrm{Tl}$. The coincidence technique allowed a separation of autoionization x rays from internal-conversion x rays and simplified the normalization of the $K$-shell autoionization probability $P_K$. The experimental value of $P_K$ obtained was (1.1 ± 0.35) × ${10}^{-5\mathrm{}}$, in good agreement with the theoretical prediction of Law and Campbell.

[RADIOACTIVITY ${}_{}{}^{203}{}_{}{}^{}\mathrm{Hg}$; measured $\gamma$-x-ray coinc; deduced autoionization probability $P_K$.]

• Received 1 November 1973

DOI:https://doi.org/10.1103/PhysRevC.9.1529