Experience in the use of FeSO4 in some practical aspects of high-energy electron dosimetry

The advantages of FeSO4 are discussed with respect to three applications in practical high-energy electron dosimetry: (1) the calibration of ionization chambers, (2) the evaluation of the importance of ion recombination in chambers exposed to high dose-rates and (3) the determination of absorbed dose in radiobiological samples. The absorbed dose conversion factor, Csub(E), of an ionization chamber can be determined by comparison with FeSO4 for electron energy E. In fact, the variation of response of the FeSO4 dose meter (or the G-value) as a function of the beam quality is very small for 60Co and electrons in the usual energy range. An FeSO4 dose meter can also be used to evaluate the importance of ion recombination in a chamber exposed to high dose-rates of electrons, since its response is independent of dose-rate (up to 2 x 108 rad.s-1). Examples are given to illustrate the interest of FeSO4 for measurements of absorbed dose in biological samples, mainly in depth in electron beams where the dose gradient is high. FeSO4 can be assumed to be insensitive to energy variation in depth (or to dose-rate variation); it does not introduce any heterogeneity and no displacement factor has to be applied; finally, the dose meter solution can occupy a volume identical to that of the biological systems to be irradiated. For these three applications, the results obtained with FeSO4 are compared with those obtained with other dosimetric systems. (author)