Absolute determination of high-energy electron dose in the light of recent results in ionization dosimetry

For high-energy monoenergetic electrons incident on an absorbing medium, the physical problems based on the Bragg-Gray principle arise essentially from the fact that the total flux of electrons and their energy spectrum vary relatively rapidly in matter. Consequently, the conditions for applying the cavity principle are never achieved exactly in practice. The cavity theories have to be accompanied by experimental proofs. From the measurements obtained with a graphite extrapolation chamber of an improved kind for 5 and 15 MeV electrons it was possible to achieve the conditions for particle equilibrium of two kinds: the exact and the ''restricted or partial'' equilibrium. It was possible to demonstrate that both kinds of equilibrium can be used to determine a dose equivalent to the cavity dose. Absolute dose determinations have been performed. Their accuracy and precision are discussed in detail and compared with the existing absolute methods within the framework of the DIN and ICRU recommendations. (author)