Ferrous sulphate dosimetry for electrons. A re-evaluation.

A theory was developed for the perturbation correction to be applied in the calorimetric determination of the ferrous sulphate dosimeter G-value. Recent determinations of the molar extinction coefficient, epsilonm, have shown that systematic errors in epsilon may have influenced experimental G-values. With precision spectrophotometers this error is cancelled in the product epsilonm.G. It was shown that after applying the perturbation correction a very small spread was obtained in calorimetric epsilonm.G-values; the standard error of the mean being 0.2 per cent. The mean G-value is 2.3 per cent lower than that recommended in ICRU Report No. 21.