An Experimental Study of the Relative Intensities of X-Ray Lines in the L-Spectrum of Thorium

The relative intensities of the thorium $L$-series lines have been measured at 31.8 kilovolts using an ionization chamber spectrometer. In addition to the lines previously reported by other investigators, the lines $\mathrm{Th}L\eta$, $\mathrm{Th}L{\beta }_7$, $\mathrm{Th}L{\gamma }_2$ were found. No indications of $\mathrm{Th}L{\gamma }_5$ or $\mathrm{Th}L{\gamma }_4$ could be found. The relative intensities have been corrected for absorption in the mica windows and air in the path from x-ray tube to ionization chamber, and for the fraction of the radiation absorbed in the methyl iodide in the ionization chamber. It was found that in the voltage range between the critical excitation voltage $V_0$ and 31.8 kilovolts, the intensity of $\mathrm{Th}L{\alpha }_1$ or $\mathrm{Th}L{\beta }_{1,5}$ at any voltage $V$ could be expressed by $I=k{(V-V_0)}^2$ within the limits of experimental error. Using this expression the relative intensities at 31.8 kilovolts were extrapolated to the relative intensities at high voltage, to which it was assumed the theoretical predictions apply. The intensity rules for doublets hold for lines involving the levels $L_{21}$ and $L_{22}$. The predictions of Wentzel based on Schrödinger's new quantum mechanics for the relative intensities of "sharp" and "diffuse" series doublets are confirmed, but the experimental intensities of the "principal" series doublets are too low by a factor of 7. They are also too low in the measurements of Jönsson on tungsten. The results obtained are as follows: