Measurement of Absolute X-Ray Intensities and Absolute Sensitivity of X-Ray Film with a Geiger-Müller Counter

A special Geiger-Müller counter for measuring absolute intensities of x-rays of known wave-lengths is described. The rays pass through the counter in such a way that only electrons set free in the gas of the counter are counted. The absorbing gas column is krypton at 6.31 cm pressure, 1.08 cm thick, and 0.0062 ${\mathrm{cm}}^2$ in cross section. For fluorescent Zr $K$-rays, the absorption in the counter is 3.75 percent, as computed on the basis of the energy distribution of the radiation: $K\alpha :K\beta :K\gamma =0.829:0.154:0.017\mathrm{}$, and absorption coefficients computed from Richtmyer and Warburton's formulae. A "standard beam" of fluorescent Zr-rays from a specially constructed x-ray tube has been calibrated with the counter. With this beam, the minimum exposure of x-ray film for detectable blackening is found to be about 0.72×${10}^6$ quanta ${\mathrm{cm}}^{-2\mathrm{}}$, incident on the film, or 4.1×${10}^4$ quanta ${\mathrm{cm}}^{-2\mathrm{}}$ absorbed in the emulsions (Eastman Ultra-Speed Duplitized X-Ray Film). The total absorption coefficients of the film, celluloid, and emulsion, for the Zr-rays, are found to be, respectively, 8.63 ${\mathrm{cm}}^{-1\mathrm{}}$, 1.66 ${\mathrm{cm}}^{-1\mathrm{}}$ and 13.0 ${\mathrm{cm}}^{-1\mathrm{}}$. Time-blackening curves are given. These show discontinuities at exposures of about ${10}^7$ quanta ${\mathrm{cm}}^{-2\mathrm{}}$.