Implication of electron backscattering for electron dosimetry

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Abstract
The electron backscatter data derived by Klevenhagen et al. (1982) and Hunt et al. (1988) were found to correlate well and were fitted to an empirical exponential expression valid between 3 and 35 MeV and atomic numbers between 4 and 82. In evaluating the formula, a (Z + 1) term was used at low atomic numbers and Z alone for higher Z scatterers. The effective atomic number formula for compounds proposed by Baily (1980) was found to give a satisfactory fit for both plastics and elements. An equation given enables the calculation of correction factors for the chamber underresponse due to backscatter deficiency. This can be done for plastics used in the construction of electron chambers, provided the Zeff is known. Apart from backscatter, the chamber sensitive volume may also receive some side scatter from the side wall. The dose perturbation due to the laterally scattered electrons in the vicinity of an interface was considered by Werner (1985). He observed similarity in magnitude between these two effects. In evaluating the side scatter, the penetration of the scattered electrons needs to be considered (Lambert and Klevenhagen, 1982).