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

The relative intensities of 17 lines in the $L$ spectrum of uranium have been measured as a continuation of the work previously reported on thorium (Allison, Phys. Rev. 30, 245 (1927)). Changes in the apparatus are described which reduce the magnitude of the corrections to be applied. The variation of the intensity of U $L{\alpha }_1$ with voltage has been studied and may be closely represented by $I=C{(V-V_0)}^{1.8}$, and with less accuracy by a function $I=C(\frac{(V-V_0)}{V_0}-log(\frac{V}{V_0}\left)\right)$ developed by Rosseland. The observed results at 52.8 kv have been extrapolated to the relative intensities at voltages very much greater than the critical voltages. Important results are: (1) The lines ${\gamma }_3{\gamma }_2$ and ${\beta }_3{\beta }_4$, known in other elements to deviate from the sum rule predictions have equal intensities in uranium although a ratio 2:1 is predicted. (2) The lines ${\gamma }_6{\beta }_5$ are 17 times more intense in uranium than in tungsten due presumably to the filling of the $5_3$ orbits in the intervening elements. (3) The lines ${\gamma }_4{\gamma }_5$ which are present in the tungsten spectrum are absent in the uranium and thorium spectra. It is shown that if Rosseland's function (above) holds for electron collisions in which the velocity of the impinging electron is great compared to the velocities of the electrons in the atom, that the relative intensities of lines of a multiplet under these conditions are equal to the product of the transition probability by the statistical weight of the initial state with only a slight correction. The results are: