Thumbnail
Access Restriction
Open

Author Nilsson, B.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY ♦ RADIOLOGY AND NUCLEAR MEDICINE ♦ IONIZATION CHAMBERS ♦ PERTURBATION THEORY ♦ ELECTRONS ♦ EXTRAPOLATION CHAMBERS ♦ PHOTON BEAMS ♦ RADIATION DOSES ♦ RADIOTHERAPY ♦ BEAMS ♦ DOSEMETERS ♦ DOSES ♦ ELEMENTARY PARTICLES ♦ FERMIONS ♦ LEPTONS ♦ MEASURING INSTRUMENTS ♦ MEDICINE ♦ NUCLEAR MEDICINE ♦ RADIATION DETECTORS ♦ RADIOLOGY ♦ THERAPY ♦ Radiation Instrumentation- Radiation Dosemeters ♦ Medicine- External Radiation in Therapy- (1980-)
Abstract The perturbation effect in parallel-plate ionization chambers used for buildup measurements has been investigated. The fluence perturbation due to electrons emitted through the side walls are thoroughly investigated by measurements using film and extrapolation chambers and by calculations. The electron fluence varies both with side wall material and chamber geometry. In order to obtain a small perturbation effect, the chamber should have a large guard width compared to the electrode separation and the side walls should have as large an angle as possible with the central axis. The side wall should be of the same material as the rest of the chamber. The perturbation effect is also dependent on the electron contamination of the beam and angular distribution of the electron fluence. It is thus not possible to correct the perturbation effect in one parallel-plate chamber with fixed plate separation with correction factors obtained with extrapolation chambers of other dimensions. In order to make accurate surface dose measurements extrapolation chambers are therefore strongly recommended in favor of fixed parallel-plate chambers.
Educational Use Research
Learning Resource Type Article
Publisher Date 1986-03-01
Publisher Place United States
Journal Med. Phys.
Volume Number 2
Organization Karolinska Institute, Stockholm, Sweden


Open content in new tab

   Open content in new tab