ABSTRACT
Objective:To study the correction factor of the chamber wall of the reference air kerma rate reference ionization chamber (NIM-Ir-SG-100 type) for 192Ir radioactive source. Methods:The photon spectrum and ionization chamber wall correction factor of the radioactive source housing and irradiator model are calculated by Monte Carlo code. And then the photon energy, wall thickness and ionization chamber diameter, which affect the result of the chamber wall correction factor, are simulated.Results:After calculation, the simulation result of the correction factor of spherical graphite cavity ionization chamber wall was 1.037 7. Controlling a single variable, photon energy (0.3-1.3 MeV), wall thickness (0.2-0.5 cm), inner diameter (0.5 -15 cm), the maximum deviations of wall correction result were 1.62%, 3.30% and 2.86%, respectively.Conclusions:The self-made spherical graphite cavity ionization chamber has good performance, and the corrected kwall value of the chamber wall is within a reasonable range. The completion of the chamber wall correction factor is an important step to measure the reference air kerma rate of the 192Ir radioactive source and establish the measurement benchmark.
ABSTRACT
Objective To investigated the absorbed dose response of Al2O3 dosimeter in water phantom irradiated by 60Co γ spectrum source. Methods The EGSnre simulation program code DOSRZnrc was used to calculate the absorbed dose of the Al2O3 dosimeter and that of the equivalent volume of water in the corresponding position, as well as the absorbed dose conversion factor, irradiated by 60Co photon beams in a water phantom. Simulations were done for a eylindrieal geometry dosimeter (diameter 0.4 cm and height 0.1 cm) and the dosimeter was placed at the centre of the water phantom at different depths. Results The average absorbed dose conversion factor is 1.143 ± 0.006 and changes little with the depth of the dosimeter in the water phantom, and the deviation is less than 1.0 %. Conclusion The absorbed dose response of Al2O3 dosimeter irradiated by 60Co γ spectrum source is steady and is independent on the depth of the dosimeter in water phantom in this research.