Journal
BIOMEDICAL PHYSICS & ENGINEERING EXPRESS
Volume 8, Issue 1, Pages -Publisher
IOP Publishing Ltd
DOI: 10.1088/2057-1976/ac3e89
Keywords
stopping power ratio; primary air kerma standard; graphite-walled cavity chamber; free-air ionization chamber; Monte Carlo EGS5
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This passage discusses the calibration of radiation dosimeters and dose-rate meters by the National Metrology Institute of Japan using a cylindrical graphite-walled cavity ionization chamber, extending the energy range of x-ray reference field measurement. Evaluation of deviations from the Spencer-Attix cavity theory was done by comparing measurement results with free-air ionization chambers, showing consistent calibration coefficients in the energy range of 300-450 kV.
Accurate radiation dosimetry is required for radiation protection in various environments. Therefore, dosemeters and dose-rate meters must be calibrated in standard radiation fields. The National Metrology Institute of Japan (NMIJ) expands the energy range of x-ray reference field measurement up to 450 kV using a cylindrical graphite-walled cavity ionization chamber. Departure from the condition of the Spencer-Attix cavity theory was evaluated by comparing the measurement results obtained using the cavity ionization and the free-air ionization chambers, which are used as the primary standard up to a tube voltage of 250 kV. The calibration coefficients found using the spherical ionization chamber were in good agreement with those obtained by the free-air ionization chamber within relative standard uncertainties (k = 1) for N-200 and N-250 x-ray fields. Consistent calibration coefficients were obtained in the energy range 300-450 kV.
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