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High‐energy‐photon dose measurements using exposure‐calibrated ionization chambers
Author(s) -
Kutcher G.,
Strubler K.,
Suntharalingam N.
Publication year - 1977
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 - 10.1118/1.594327
Subject(s) - ionization chamber , ionization , cobalt 60 , dosimetry , photon , cobalt , materials science , absorbed dose , dose profile , volume (thermodynamics) , doubly labeled water , environmental science , atomic physics , computational physics , physics , nuclear medicine , optics , ion , nuclear physics , irradiation , energy expenditure , medicine , quantum mechanics , metallurgy , endocrinology
The current method for determining absorbed dose from high‐energy photons is to use in water a Cobalt‐60 exposure‐calibrated ionization chamber and C λ . Recently questions have arisen about the correctness of currently recommended C λ values and whether or not the Cobalt‐60 buildup cap should be used for in‐water dose measurements. The effect of the buildup cap on C λ was obtained by measuring Farmer chamber response in water with and without the buildup cap. Results show no measurable change at Cobalt‐60 or 4 MV but an increase of 1%–2% above 20 MV. The effects of the wall materials and the displacement factors on C λ are also considered. It is shown that at high energies errors of 3%–5% can be made in determining dose in water using commercially available Farmer or Farmer‐like chambers and currently recommended C λ . The exact size of the error depends upon the materials and thicknesses of the wall and cap, the chamber cavity volume, and whether or not the buildup cap is used.