The probability that a Pb $M$ photon is emitted in ${\mathrm{Po}}^{210}$ decay is 0.91(±15%)×${10}^{-3\mathrm{}}$ photons/alpha, as measured by means of a proportional counter and pulse-height analyzer. This value is in gross disagreement with theoretical estimates. A Pb $M$ spectrum from ${\mathrm{Po}}^{210}$ decay shows definite differences from a conventional Pb $M$ spectrum, indicating considerable ejection of higher shell electrons in the ${\mathrm{Po}}^{210}$ decay act. In particular, the spectrum from ${\mathrm{Po}}^{210}$ contains a 3.7-keV component whose intensity is about 4% of the total spectral intensity and whose energy is consistent with the allowed, but hitherto unreported, transition $M_1{O}_{23}$. The theory of electron ejection in alpha decay is reviewed and previous calculations of ejection probabilities are extended to include ejection to bound states. The estimates of $K$, $L$, and $M$ photon yields on this theory are orders of magnitude lower than the measured yields. Possible sources of the discrepancy are discussed.

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