The absolute intensity of $L$ x-rays/RaD disintegration ($F$) has been measured to be ${0.23}_8$±0.02 by argon-filled proportional counter spectrometry on carrier-free RaDEF equilibrium sources, and the relative intensities were found to be $L_{\alpha }:L_{\beta }:L_{\gamma }\colon\colon 1.0:1.1:0.19$. The intensity of $L$ x-rays relative to that ($R$) of the single, 46.5-kev, pure $M1\mathrm{}$ gamma ray is $\frac{F}{R}=5.1\mathrm{}\pm 0.7$. Care was taken to avoid error due to wall-effects and the counting techniques were varied and cross-checked so as to eliminate possible systematic errors. The absolute intensity of the gamma ray is $R=0.045\mathrm{}\pm 0.004$ from data taken on a 3×3 inch NaI(Tl) scintillation spectrometer. Assuming the number of $L$-shell ionizations/RaD disintegration ($I$) to be 0.62, the mean $L$-fluorescence yield ($\frac{F}{I}$) of bismuth is 0.38±0.02, which when combined with the ratio $\frac{F}{R}$, leads to an experimental value of the total $L$-shell conversion coefficient ($\frac{I}{R}$), which thus is 13.3±2.0, the major error arising from the correction of $R$ for the contribution due to Compton backscattering, which amounts to some 10 to 20% depending on exact conditions of geometry and collimation. The value of the $L$-conversion coefficient interpolated from Rose's tables is 17.85, based on a point-charge nucleus. Better agreement is obtained with a value of about 12.7 from theoretical calculations of Sliv and Listengarten, who included a correction for the finite size of the nucleus.

A new summary of mean $L$-fluorescence yields from nuclear excitation is presented which shows that the mean yields depend strongly upon the relative number of vacancies in the respective $L$ subshells.

• Received 26 December 1956

DOI:https://doi.org/10.1103/PhysRev.106.266