Influence of cavity size on the response of cavity chambers to 25- and 45-MeV neutrons.
We calculated the response of gas-cavity dosimeters to 25- and 45-MeV neutrons in order to estimate the portion of the response that originates from neutron interactions within the gas cavity. This affords insight into the validity of the Bragg-Gray theory for dosimeters with finite cavities and also provides a basis for modifying gas-to-wall absorbed dose conversion factors deduced from the Bragg-Gray theory for use with small-cavity dosimeters. For a typical ionization chamber, e.g., with a 1-cm3 propane-based tissue-equivalent gas at standard temperature and pressure, the fraction of the total absorbed dose to the gas cavity from neutron interactions within the gas is 0.09% at 25-MeV and 0.006% at 45-MeV neutron energies. For microdosimetric detectors, the neutron interactions within the gas are negligible above 25 MeV.
Newhauser
W D
WD
Physikalisch-Technische Bundesanstalt, Braunschweig, Germany.
Brede
H J
HJ
D005214:Fast Neutrons / Q000627:therapeutic use*; D005740:Gases; D006801:Humans; D008962:Models, Theoretical; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted
D005740:Gases