Abstract
Backscattered photons from slab phantoms were analyzed to investigate the effects of phantom size and material on calibration of dosimeters. The backscatter factor estimated by measurement with an ionization chamber was compared for three different phantoms ; a 40× 40×15 cm3 polymethyl methacrylate (PMMA) phantom, a 30×30×15 cm3 PMMA phantom and a water-filled phantom recommended by the International Organization for Standardization (ISO) . Monte Carlo calculations using EGS4 code were also performed to examine the measured results and to analyze the effect of phantom size and material on the dosimeter calibration. It was found that the ISO phantom could give up to 10% higher value of calibration factor than the 40×40×15 cm3 PMMA phantom, now commonly used in Japan, for photons of 60 keV.
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