Experimentally determined backscatter factors for X-rays generated at voltages between 16 and 140 kV

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Abstract
The backscatter factors computed by Grosswendt (1984) for X-rays generated at voltages between 10 and 100 kV using a Monte Carlo method differ significantly from the corresponding factors published in supplement 17 of the British Journal of Radiology (1983). The data may be subject to systematic uncertainties and it was therefore thought necessary to undertake a study of the backscatter in a uniform experiment in order to verify these data and the theoretical calculations of Grosswendt (1984). A special 3 mm thin plane-parallel ionisation chamber was constructed for this work and measurements were performed using water as a scattering medium. The experiments involved field sizes of 2.0 to 20 cm beam diameter and X-ray qualities between 0.1 and 4 mm Al for generating voltages between 16 and 140 kV. The results yielded backscatter factors which are in close agreement with those obtained by Monte Carlo calculations. The agreement with the supplement 17 data is only satisfactory at HVLs above 1 mm Al. The possible causes for the disagreement between the various published data are analysed.