British Journal of Radiology · 1980 · 15 citations · 2 references
MedicineNuclear EngineeringNuclear MedicineRadiation DosimetryRadiation MeasurementRadiation PhysicsGamma-ray InstrumentationIonization Chamber DosimetryIonization ChambersPhantom DosimetryPhoton DosimetryRadiation Dose MeasurementDisplacementEffective Point Of MeasurementFarmer-type Ionization Chamber DosimetryGamma DosimetryIonizing Radiation DosimetryThimble Ionization ChambersWater Phantom MeasurementsX-ray Dosimetry
The effective point of measurement for spherical ionization chambers has been determined for 60Co and 137Cs gamma rays and for 300 kV X rays inside a water phantom. For reasons of comparison, measurements were also performed with a thimble-type Baldwin-Farmer ion chamber. For spherical ion chambers the displacement correction factors were 1-(0.37 +/- 0.04) r. 10(-2) for 60Co gamma rays and 1-(0.22 +/- 0.05) r. 10(-2) for 137 Cs gamma rays, where r is expressed in mm, whereas no displacement was observed for X rays. The differences in displacement obtained for the various types of radiation can be attributed to differences in attenuation and scatter characteristics of the various radiation qualities.
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