A measurement of the relative intensities of the $K$ and $L$ x-rays following electron-capture in ${\mathrm{Cs}}^{131}$ is reported. The result may be expressed $[\frac{L_{\mathrm{I}}}{K}+\frac{K_{\mathrm{I}\mathrm{I},\mathrm{I}\mathrm{I}\mathrm{I}}}{K}+n]{\overline{\omega }}_L=0.106\mathrm{}\pm 0.008$, where $\frac{L_i}{K}$ is the ratio of $L_i$-shell capture to $K$-shell capture, $n$ is the probability of an $L$-ionization following a $K$-vacancy, and ${\overline{\omega }}_L$ is the mean $L$-fluorescence yield of xenon. Upon combining this with recent theoretical results on electron-capture, the mean value of the $L$-fluorescence yield of xenon is found to be ${0.10}_3$±0.01. This value is suggested as a normalization point for the relative photographic values of ${\overline{\omega }}_L$ in the region $Z=54\mathrm{}$.

In order to explain the observed anomalies in inner bremsstrahlung spectra of electron-capture on the basis of $p$-electron capture, one must conclude that $L_{\mathrm{II}}$-capture is considerably more radiative than $L_{\mathrm{I}}$-capture, and, furthermore, that the probability of radiative capture increases more strongly with $Z$ for $L_{\mathrm{II}}$-capture than for $L_{\mathrm{I}}$-capture.

Traces of 6.2-day ${\mathrm{Cs}}^{132}$ and 13.6-day ${\mathrm{Cs}}^{136}$ were found in the first cesium fraction from pile-irradiated barium nitrate, presumably induced by ($n, p$) reactions.

• Received 3 January 1955

DOI:https://doi.org/10.1103/PhysRev.98.1293