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Examination of the factors A/sub c/ and A/sub eq/ for cylindrical ion chambers used in cobalt-60 beams

Journal Article · · Med. Phys.; (United States)
OSTI ID:5985688
; ; ;

The calibration of a cobalt-60 beam in a phantom with an ion chamber, which has been calibrated with respect to exposure, requires the use of a displacement correction factor which essentially corrects the photon fluence for the attenuation and scatter when the chamber with buildup cap is removed and replaced by phantom material. To determine the displacement factor, A/sub c/, a special set of cylindrical ionization chambers with various volumes were constructed out of polystyrene. Tissue--air ratios were measured with these chambers for cobalt-60 gamma rays in a polystyrene phantom, and the ratio A/sub c//A/sub eq/ was experimentally determined. In order to calculate A/sub c/ from this ratio, A/sub eq/ was determined also. It was found that A/sub c/ depended on chamber diameter only, and not on field size or depth. A value of 0.990 for A/sub eq/ is recommended and a table of A/sub c/ for chambers of different outer diameters is included.

Research Organization:
Department of Medical Physics, Memorial Sloan--Kettering Cancer Center, New York, New York 10021
OSTI ID:
5985688
Journal Information:
Med. Phys.; (United States), Journal Name: Med. Phys.; (United States) Vol. 6:4; ISSN MPHYA
Country of Publication:
United States
Language:
English

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Related Subjects

440102 -- Radiation Instrumentation-- Radiation Dosemeters
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
61 RADIATION PROTECTION AND DOSIMETRY
655003* -- Medical Physics-- Dosimetry
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CALIBRATION
COBALT 60
COBALT ISOTOPES
DOSIMETRY
GAMMA DOSIMETRY
INTERMEDIATE MASS NUCLEI
INTERNAL CONVERSION RADIOISOTOPES
IONIZATION CHAMBERS
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
MEASURING INSTRUMENTS
MEDICINE
MINUTES LIVING RADIOISOTOPES
MOCKUP
NUCLEAR MEDICINE
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANIC POLYMERS
PETROCHEMICALS
PETROLEUM PRODUCTS
PHANTOMS
PLASTICS
POLYMERS
POLYOLEFINS
POLYSTYRENE
POLYVINYLS
RADIATION DETECTORS
RADIOISOTOPES
RADIOLOGY
RADIOTHERAPY
STRUCTURAL MODELS
THERAPY
YEARS LIVING RADIOISOTOPES