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Comparison of ferrous sulfate (Fricke) and ionization dosimetry for high‐energy photon and electron beams
Author(s) -
Kwa William,
Kornelsen Richard O.
Publication year - 1990
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.596491
Subject(s) - ionization , dosimetry , electron , dosimeter , atomic physics , photon , materials science , irradiation , absorbed dose , ionization chamber , physics , nuclear physics , radiation , nuclear medicine , optics , ion , medicine , quantum mechanics
Dose measurements using Fricke and ionization methods were compared for 60 Co gamma rays, 4–25‐MV photons, and 10–25‐MeV electrons. Fricke derived doses based on a constant yield (ε m G ) were in good agreement with ionization derived doses based on the American Association of Physicists in Medicine Task Group 21 protocol and the National Research Council of Canada (NRC) N D calibration or the NRC proposed N x . These measurements also confirmed the validity of the double‐voltage technique in the collection efficiency correction, even for swept electron beams. Assuming the correctness of the ionization derived doses, the radiation yield appeared to be 1% higher and to increase with photon energy when irradiation vessels were made of Pyrex but not with polystyrene cells. These glass wall effects could be due to the scattering perturbation of electrons between inhomogeneous materials and, in particular for photon beams, due to the mismatch in mass energy absorption ratios and mass collision stopping power ratios between the Fricke dosimeter and the wall materials.