Standard measurements of the physical properties of short wavelength X rays

Abstract

The work described covers an investigation of some of the physical problems associated with short wavelength X rays. The radiations emitted from high energy generators are discussed and it is found that the experimental results of the writer and the small number of other experimental results available do not agree with theoretical predictions for the angular distribution of the radiation. Possible explanations are given. A number of measurements of absorption coefficients of high energy radiations in various materials are reported. Values of the coefficients calculated from the theories for the various absorption processes are also given and the agreement between theory and experiment is, in general, good. a review of other measurements of absorption coefficients using various techniques and at energies up to approximately 90 MeV. show that generally speaking the theories for the various processes are substantiated. Some effects are demonstrated resulting from the change from a decrease of absorption coefficient with increasing energy to an increase with increasing energy resulting from the advent of the pair formation process. The problem of the measurement of high energy X radiation is discussed and experimental results presented which indicate that it is possible to measure the radiations in rontgens up to an energy of approximately 30 MeV. Some comparative measurements with American workers show satisfactory agreement with the dosage measuring technique of one team and demonstrate the errors introduced by the method adopted by another team. New processes which alter the effective stopping power of the materials become evident from the experimental results and values of these stopping powers are deduced. The problem of measurement of the radiation from radioactive isotopes has also been investigated and measurements made with ionisation chambers of different materials show that a satisfactory system of measurement of the dosage-rate for radiations emitted from these isotopes can be worked out from considerations of the energy absorbed. Values of stopping power calculated from these measurements show good agreement with the values given by Be the and G-ray. Measurements and calculations pertaining to the protection requirements for personnel operating high energy generators are given along with recommendations on the solution of the problem. Some photographic dosage measurements are also presented from which it is concluded that the sensitivity of photographic film measured in "blackening per rontgen" changes very slowly in this high energy region, a result to be expected theoretically. Some measurements of the distribution of radiation in and around a scattering medium and the variation of quality of the radiation inside the mass are also presented.