Dosimetry of the Very Weak X-radiation Generated in Television Receivers and X-ray Diffraction Apparatus

With many kinds of apparatus in which electron tubes are operated at high voltages, the possiblepresence of very weak, soft Xvradiation, (i.e. Xradiation of low penetrating power) in the neighbourhood must be given due consideration. The question arises in such apparatus as X-ray diffraction equipment, formerly found only in research laboratories but now widely used industrially in inspection and production departments. Television receivers, too, can emit X-rays, for inmodern largescreen sets the accelerating voltage for the electron beam in the picture tube can be as high as 20 kV at a beam current up to 0.2 mA. Fortunately this X-radiation is so soft that it can be attenuated to harmless intensities by simple means, for example by the 6 mm thick glass shield over the viewing screen, which is needed in any case as proteetion against implosion of the tube. Nevertheless it is necessary during manufacture to make dosimetrie tests to ensure that the intensity of the radiation at the outside of the set in no way endangers the user. The' International Commission for Radiological Proteetion 1) has recommended that the dose rate at the outside surface of home television receivers should not exceed 2 milliröntgens per hour (2 mr/h or 0.6 IJ-r/sec). In the future the limit will probably be set lower still, in order to preclude all possibility of genetic hazards. This possible lowering of the limit has been allowed for in the design of the dosimetrie apparatus described in this article. . In the case of X-ray diffraction apparatus, the requirements s.regarding the maximum permissible dose rate outside the useful" X-ray beam are less severe, such apparatus being used by so very small a section of the population that genetic considerations do not arise and only the norms for individual proteetion need be applied. For the industrial use of X-ray equipment the recommended maximum permissible dose rate 'outside the useful beam is 6 mr/h. The dose rate of 'very weak, soft X-radiation, such as that from television receivers, can be checked ~th Geiger-Müller counter tubes :fitted with a window ofthin mica (approx. 15 IJ-).Such tubes are