Comparison of ionization, ferrous sulphate and thermoluminescence dosimetry of megavoltage photons

For 60 Co gamma -radiation and 8, 15 and 33 Mv x-rays, dose measurements made, using (a) a calibrated Farmer-Baldwin dosemeter and C lambda values recommended by I.C.R.U., and (b) FeSO 4 solution and G-values recommended by I.C.R.U., are compared. Differences between the results are within 5%, and increase with increasing photon energy. FeSO 4 results always being the greater. The relative response of LiF TLD powder to these radiations has also been compared with ionization measurements. On the assumption that the C lambda values are substantially correct, and that for 60 Co radiation G=15.5, the data give FeSO 4 G-values of 16.1+or-0.2 at 8 Mv, 15.9+or-0.2 at 15 Mv and 16.3+or-0.2 at 33 Mv. These are in good agreement with the few literature values for photons in this energy region, but are not consistent with literature values for high energy electrons.