An Experimental Test of the Ionization Chamber Method of Measuring the Relative Intensities of X-ray Spectrum Lines

A two-compartment ionization chamber has been constructed with the following properties: (1) The fraction of the x-ray energy absorbed in the front compartment could be directly measured, (2) The volume of gas from which the ionic saturation current was drawn was sharply defined, (3) Photoelectrons produced in the chamber could not reach the walls before expending their ionizing energy, (4) The direct beam entered and left the chamber through thin windows and encountered no other parts of the chamber. The relative ionization currents produced in methyl iodide, methyl bromide, argon, sulfur dioxide, and air by the ${\alpha }_1$, ${\beta }_1$, ${\gamma }_1$, lines of the tungsten $L$ series were measured and the ratios obtained after correction for fraction of the direct beam absorbed were found not to vary more than 2.5 percent in the first four gases. If the air values are corrected for loss through scattering, concordant results are obtained. Similar experiments have been made using the uranium $L$-series, where large corrections for loss through escape of fluorescent $K$-radiation must be made, including the case of krypton, where the $K$ limit comes between the uranium $L{\beta }_1$ and $L{\alpha }_1$ lines. The results give strong support to the following hypothesis: The saturation current obtained from a given volume of any gas is proportional to the fraction of the x-ray beam transformed into $\beta$-rays within it, providing the $\beta$-rays come to the end of their ionizing range within the volume.