Dead Time and Non-Linearity Characteristics of the Geiger-Counter X-Ray Spectrometer

The satisfactory use of Geiger-counter methods for the measurement of diffracted x-ray intensities demands that the observed counting rates be corrected for the non-linear response of the counter. Both the multiple foil method of calibrating the non-linearity of response and the two-source method of Beers for measuring counter dead time have been found to be unsatisfactory approaches to this problem. The experience of this laboratory indicates that electronically controlled oscillographic techniques for the direct measurement of dead time are much more satisfactory. With a knowledge of the dead time, τ, the true counting rate, N, can be calculated from the observed counting rate, No, by employing the formula N=No/(1−Noτ). For a pulsating x-ray source the effective counting rate is faster than the observed by a factor which is characteristic of the type of rectification employed, the target material, and the voltage applied to the x-ray tube. A sufficiently accurate value of this factor can be arrived at by oscillographic observation of the pulse pattern and in some cases by mathematical analysis.