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N gas determination for a parallel‐plate ion chamber
Author(s) -
Krithivas G.,
Rao S. N.
Publication year - 1986
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 - 10.1118/1.595872
Subject(s) - ionization chamber , dosimetry , calibration , imaging phantom , ion , irradiation , materials science , atomic physics , cathode ray , fluence , beam (structure) , electron , optics , physics , nuclear medicine , nuclear physics , ionization , medicine , quantum mechanics
A parallel‐plate ion chamber has been investigated with a view to determining N gas , the cavity‐gas calibration factor, introduced by the Task Group 21 protocol for dose determination. In‐air and in‐phantom irradiation of a Memorial Hospital parallel‐plate ion chamber in a 6 0 Co beam led to the determination of ion collecting volume and a calibration factor for the chamber. When these quantities were used to deduce N gas factors for the chamber, an agreement within 1% was found. An average of the cavity‐gas factors obtained from 6 0 Co data agreed to within 0.5% with the factor determined through force fitting the doses received by the parallel‐plate chamber and a cylindrical chamber in a 22‐MeV (nominal) electron beam. Additionally, the parallel‐plate chamber was utilized to study the effectiveness, in electron beam dosimetry, of the electron fluence perturbation correction factors introduced when the phantom material is replaced by a cylindrical ion chamber.