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An X-ray Output Meter

Barnato Joel Laboratories, The Middlesex Hospital

This excerpt was created in the absence of an abstract.

The technique of measuring the intensity of a beam of X rays at the aperture of a tube has been utilised in some therapy equipments, and a few commercial instruments have been made for this purpose. An instrument of this type has the merit that it allows the tube output to be controlled and maintained constant regardless of changes in mains voltage or in parts of the apparatus such as rectifying valves, which affect critically the X-ray generation.

Such instruments have as a rule been somewhat delicate, and do not in general seem to have proved as reliable as is required for clinical work. In view of this and their high cost, their use has been very limited. It seemed, therefore, that some more robust form of meter which was at the same time relatively inexpensive would have a useful application, and would assist considerably in the control of dosage in therapeutic work. Some attempt has been made to meet this need, and it has been found that the instrument described below satisfies the requirements to a large extent, with a minimum of cost and equipment.

The basis of the instrument is an ionization chamber fitted into the tube aperture, through which the rays pass. The current through the chamber, when saturation is maintained in it, is then a measure of the intensity of the X-ray beam.