[The use of the residual range as the exclusive energy parameter in electron dosimetry]

A commonly used procedure to determine the absorbed dose to water in a high energy electron beam is based on the assumption that the response of an air-filled plane parallel chamber for this quantity is only a function of the difference between practical range and measuring depth (the residual range). This procedure is said to be applicable to almost all electron energies and spectra in practical use. The response of a plane parallel chamber in a water phantom was determined by means of ferrous sulphate dosimeters in radiation fields of a linear accelerator. The results show that the residual range is insufficient as the only energy parameter.