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The relative merits of tungsten and molybdenum targets for mammography have been the subject of much discussion. Therefore the spectra and outputs (at constant potential) from molybdenum and tungsten targets, interchangeable in the same tube, have been measured with a Ge(Li) detector and ion chamber respectively. All conditions apart from the target material were unaltered. The spectra have been corrected for the distortions produced by the detector. The effects of filtration on spectra and exposure rates have been calculated and are in agreement with measured values. The spectra and outputs from molybdenum and tungsten targets filtered by aluminium and molybdenum have been investigated and the results are discussed with reference to mammography and the radiography of specimens.

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Radiation protection recommendations give requirements for nitration of X-ray tubes, and to conform with these it is necessary to know the inherent filtration. Methods described for its determination and the discrepancies in the results given by reputable authors are discussed. Output measurements given in handbooks of standard data may be misleading if compared with such data for tubes for which the inherent filtration is in doubt. The importance of the correct effective kV at which measurements are made is discussed. The target angle of the tube has an important effect in altering X-ray quality. If the same target angle is not used for both calibration and measurements, discrepancies can result which can easily lead to an erroneous value of inherent filtration of between 0-25 and 0-5 mm of aluminium equivalent. A procedure is described using our copper reference number method which enables calibration curves to be obtained so that the inherent or total filtration of an X-ray tube may simply be determined with an accuracy better than 0-1 mm Al equivalent.

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