Relative Intensities and Transition Probabilities of theK-Series Lines of the Elements 24 to 52 by the Ionization Chamber Method

Abstract

Experiments on the ionization currents produced by x-ray lines of wave-lengths 2.29, 1.93 and 1.66A entering a double ionization chamber filled with methyl iodide, methyl bromide, argon, air, and sulphur dioxide have been carried out. The current ratios obtained when corrected for the fraction of the direct beam absorbed in the front chamber were found not to vary by more than 1.5 percent in these gases. The conclusion is reached that the ionization chamber is a suitable instrument for measuring relative intensities of x-ray lines of different wave-lengths in the region 0.4 to 2.3A. The relative intensities of the $K$-series lines of twenty elements from Cr (24) to Te (52) were examined under controlled conditions and on correction for various factors yield a variation of relative intensity with atomic number. $\frac{{\alpha }_2}{{\alpha }_1}$ remains constant at approximately 0.50 throughout the range. $\frac{{\beta }_1}{{\alpha }_1}$ rises steeply from a value of 0.161 at Co (27) to 0.274 at Sr (38) then less rapidly to 0.306 at Te (52). $\frac{{\beta }_2}{{\alpha }_1}$ rises steeply from a value of 0.0036 at Zn (30) to 0.0450 at Zr (40) and then in a more linear fashion to 0.0735 at Te. Equations obtained from measurements on the absorption coefficients of various materials are: $\mathrm{Mica} \mu =36.56\mathrm{}{\lambda }^{2.76} \mathrm{from}0.4\mathrm{to}2.3\mathrm{A}$ $\mathrm{Cellophane} \mu =3.52\mathrm{}{\lambda }^{2.66} \mathrm{from}0.6\mathrm{to}2.3\mathrm{A}$ $\mathrm{C}{\mathrm{H}}_3\mathrm{Br} \frac{\mu }{\rho }=19.2\mathrm{}{\lambda }^{2.79} \mathrm{from}1.1\mathrm{to}2.3\mathrm{A}$ $\mathrm{C}{\mathrm{H}}_3\mathrm{I} \frac{\mu }{\rho }=65.46\mathrm{}{\lambda }^{2.62} \mathrm{from}0.4\mathrm{to}0.9\mathrm{A}.$ A treatment is given and discussed for the absorption of the x-rays within the target. The resultant correction is small and on application to the observed relative intensities the ratio of the transition probabilities for the $K$-series lines of these elements is obtained.