Ionising radiations: precautions for industrial users.

  • Great Britain. Department of Employment and Productivity.
Date:
1969
Catalogue details

Licence: Public Domain Mark

Credit: Ionising radiations: precautions for industrial users. Source: Wellcome Collection.

    39/76 (page 37)
    should be used. Particular care must be taken when ‘lining up’ the apparatus to prevent the exposure of operators’ eyes. This is usually effected with the aid of a small fluorescent screen to indicate the centring of a specimen or the correct passage of the useful beam through a camera-slit system. This can be done even with the apparatus inside a cabinet because the fluorescent screen can be built into the wall of the cabinet. Where, however, this is not practicable, neither the eye nor any other part of the body should be in a direct line with the main beam, which should be stopped by a lead disc or other absorber, preferably fixed permanently to the camera or table of the instrument. When it is not possible to enclose the apparatus totally in a cabinet, alternative precautions are necessary and they vary accor- ding to the two main conditions of use, which are: 1 Where a camera or diffraction apparatus is attached directly to the X-ray tube window and there does not have to be a gap between the two, and 2 Where there has to be a gap between the tube window and the diffraction apparatus, e.g. in the open type of construction usual with counter-diffractometers such as those used for checking quartz crystals. In both cases, suitable shutters at the X-ray tube windows are necessary. Shutters must move easily in their guides without the risk of sticking in the open position and they should operate in such a way that, in the event of failure of the electrical supply, they fall under gravity into the closed position. When the camera or other apparatus is attached directly to the window (condition 1) an interlock should be provided so that 1 The shutter cannot open unless the camera and other apparatus is in position and will close when the camera is removed, or 2 The X-ray tube cannot be energised unless the camera is in position and will be de-energised when the camera is removed. In practice it is not usual for the X-ray tubes of diffraction apparatus to be switched on and off frequently because this can affect the stability of the radiation outputs. Because a single interlock can be inadvertently operated, it is preferable for two interlocks to be fitted. They must be located very carefully because they must operate only when the camera is in the exact position and no leakage of radiation between the window of the tube and the camera is possible. Appreciable scattering can occur in the gap between the X-ray tube and the camera etc. and the design of the coupling between the camera and the window should be such as to prevent this happening. This is usually achieved by making the coupling a labyrinth which produces a multiple path for the scattered radiation. When the apparatus is of the open-type construction (condition 2) protection can be provided either by: