Search for DoubleK-Shell Ionization in the Decay ofXe131m

The deexcitation of the $h_{\frac{11}{2}}$ isomeric 164-keV level in ${\mathrm{Xe}}^{131m}$ has been reinvestigated for the possible simultaneous emission of two $K$-conversion electrons. The double-decay process was searched for by observing the x-ray coincidence spectrum with Ge(Li)-NaI(Tl) and Ge(Li)-Si(Li) coincidence spectrometers. Although the characteristic x ray of xenon was actually observed in the coincidence spectrum, it was found that this was not primarily due to the simultaneous emission of two $K$ electrons. Our experiment places an upper limit on the possible occurrence of double $K$-electron emission per single-photon decay: $\frac{W_{e_K{e}_K}}{W_{\gamma }}<1.4\mathrm{}\times {10}^{-3\mathrm{}}$. From the observed photon spectrum in coincidence with $K$ x rays, an upper limit of 2×${10}^{-2\mathrm{}}$ is obtained for the probability of $e_K-\gamma$ transitions per single-photon decay.