Fraction of ionization from electrons arising in the wall of an ionization chamber

Journal Article · Sat Jan 01 04:00:00 EST 1983 · Med. Phys.; (United States)

DOI:https://doi.org/10.1118/1.595288· OSTI ID:6507689

Lempert, G D; Nath, R; Schulz, R J

The accuracy of high-energy x-ray dosimetry can be improved by taking account of differences between the compositions of the chamber wall and the buildup cap or dosimetry phantom. The fraction of the ionization due to secondary electrons arising in the chamber wall has been determined as a function of wall thickness for /sup 60/Co gamma rays and x rays in the range of 2--25 MV for Farmer-type chambers. Secondary electrons arising in the accelerator head were removed from the x-ray beams by a magnetic field placed just in front of the ionization chamber. For /sup 60/Co gamma rays, the fraction increases from 40% to 100% as the wall thickness increases from 0.05 to 0.55 g cm/sup -2/. For a 0.05 g cm/sup -2/ wall, fraction decreases from 60% to 10% as the x-ray energy is increased from 2 to 25 MV. Limited data obtained with different chambers suggest that the fraction is independent of chamber wall composition when the thickness is expressed in g cm/sup -2/.

• Research Organization: Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, Connecticut 06510
• OSTI ID: 6507689
• Journal Information: Med. Phys.; (United States), Journal Name: Med. Phys.; (United States) Vol. 10:1; ISSN MPHYA
• Country of Publication: United States
• Language: English

Related Subjects

61 RADIATION PROTECTION AND DOSIMETRY
655003* -- Medical Physics-- Dosimetry
ACCURACY
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CHEMICAL COMPOSITION
COBALT 60
COBALT ISOTOPES
DIMENSIONS
DOSIMETRY
ELECTROMAGNETIC RADIATION
ELECTRON EMISSION
ELECTRONS
ELEMENTARY PARTICLES
EMISSION
FERMIONS
GAMMA RADIATION
INTERMEDIATE MASS NUCLEI
INTERNAL CONVERSION RADIOISOTOPES
IONIZATION
IONIZATION CHAMBERS
IONIZING RADIATIONS
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
LEPTONS
MEASURING INSTRUMENTS
MINUTES LIVING RADIOISOTOPES
MOCKUP
NUCLEI
ODD-ODD NUCLEI
PHANTOMS
RADIATION DETECTORS
RADIATIONS
RADIOISOTOPES
SECONDARY EMISSION
STRUCTURAL MODELS
SURFACE IONIZATION
THICKNESS
WALLS
X RADIATION
X-RAY DOSIMETRY
YEARS LIVING RADIOISOTOPES