Absorbed Dose in Water: Comparison of Several Methods Using a Liquid Ionization Chamber

Abstract

In the present investigation a liquid ionization chamber has been used as a transfer instrument for the quantity absorbed dose in water in a cobalt-60 gamma-ray beam. The characteristics of the liquid ionization chamber are described. The transferred dosimetric information has been compared with absorbed-dose determination using air-ionization-chamber dosimetry, water calorimetry and ferrous-sulphate dosimetry. The agreement between the different measured absorbed-dose values is very good, i.e. within 0.2%. This is an indication that the consistency in the methods used to determine absorbed dose in water is good. The impact of the new standard for air kerma in air, introduced in 1986 by the BIPM, on the air-ionization-chamber dosimetry is investigated. It is shown that any differences in the dosimetry when using the old or the new set of data cancel out for the cobalt-60 beam. The investigation also shows that the value of epsilon mG for the ferrous-sulphate dosimeter recommended in ICRU 35 for electrons can be used also in cobalt-60 beams.