Efficiency of production of x rays

Abstract

Efficiency.-The various corrections necessary for an estimate of efficiency of production Ec of continuous spectrum X rays are carefully considered. These include corrections for absorption (including absorption in the anticathode), reflection of cathode rays at the focal spot, asymmetric spatial distribution of X-ray intensity, and allowance for characteristic ray energy. Applying these corrections to some data by Rump, E c for a tungsten anticathode at a voltage V= 40 kv is found to be 0.0039. It is pointed out that E c can not yet be accurately estimated for a wide range of voltage. Present knowledge of secondary processes in gas filled tubes is so limited as to make it inadvisable to attempt to use these tubes for an exact estimate of E c. The bearing of the Thomson-Whiddington constant on the generation of X-ray energy is pointed out, and an explanation given for Ulrey's results indicating a certain degree of periodicity in the dependence of efficiency on atomic number. Intensities.-It is shown, on the basis of Rump's data, that the continuous spectrum intensity generated inside an anticathode and radiated at an angle ^ = 90° with the cathode stream is proportional to V B/2 , at least for tungsten and F>40 kv. A general formula for the spectral intensity distribution of this radiation is given, as well as a means for estimating its variation with \p; absorption in the anticathode is described quantitatively; the proportion of K characteristic rays for tungsten is found. There is thus obtained a completa description of the intensities obtainable outside X-ray tubes for a wide range of practical conditions.