Premium
Polarity effect for various ionization chambers with multiple irradiation conditions in electron beams
Author(s) -
Aget Hélène,
Rosenwald JeanClaude
Publication year - 1991
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 - 10.1118/1.596694
Subject(s) - ionization , polarity (international relations) , electron , irradiation , ionization chamber , atomic physics , beam (structure) , cathode ray , materials science , electric field , electron beam processing , chemistry , optics , physics , nuclear physics , ion , biochemistry , organic chemistry , quantum mechanics , cell
The effect of reversing the voltage polarity applied to an ionization chamber has been investigated in electron beams for several types of chambers and several irradiation conditions. It has been found that differences in readings can be significant for cylindrical chambers (about 10%) as well as for plane parallel chambers (20%). The effect is larger for large field sizes than small ones. It generally includes an appreciable stem and cable effect. Differences in readings with both polarities are related to the energy distribution of the electron beam and are greater for lower electron energies than higher. Polarity effect and charge deposit within the chamber wall material appear to be closely connected. This charge deposit, expressed as a proportion of the total collected charge, can be directly derived from double polarities measurements. Careful investigation of the effect should be made to avoid significant error (over 5%) in the determination of the absorbed dose. Key words: electrons, polarity effect, ionization chambers