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Determination of the air w ‐value in proton beams using ionization chambers with gas flow capability
Author(s) -
Moyers M. F.,
Vatnitsky S. M.,
Miller D. W.,
Slater J. M.
Publication year - 2000
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 - 10.1118/1.1308085
Subject(s) - argon , ionization chamber , nitrogen , ionization , proton , range (aeronautics) , ion , analytical chemistry (journal) , atomic physics , materials science , chemistry , physics , nuclear physics , organic chemistry , chromatography , composite material
The purpose of this work was to determine the w ‐value of air for protons using the paired gas method. Several plastic‐ and magnesium‐walled chambers were used with air, synthetic air, nitrogen, and argon flowing gases. Using argon as a reference gas, the w ‐value of air was measured and ranged from 32.7 to 34.5 J/C for protons with energies encountered in radiotherapy. Using nitrogen as a reference gas, the w ‐value of air ranged from 35.2 to 35.4 J/C over the same range of proton energies. The w ‐value was found, at a given energy, to be independent of the ion chamber used. The uncertainty in these measurements was estimated at 5.2% at the 2σ level. This uncertainty was dominated by the 4.4% uncertainty in the w ‐value of the reference gas.