Calculation of exposure rate constant for 60Co, 22Na and 111In Sources with FLUKA Monte Carlo Code

Exposure rate constant (G) relates activity of a point source to exposure rate at certain distance. It’s an important parameter in radiation protection, medical uses and radiological assessments. In this study, exposure rate constant for three radionuclides include 60 Co, 22 Na and 111 In were calculated with FLUKA Monte Carlo method. Each source was simulated and exposure rate at different distances of 20, 30, 40, 60, 80, 100, 120, 150, 200 and 300cm from the sources were measured. For dose measurements,   a farmer ionization chamber was simulated with active volume of 0.6cm 3 , inner electrode of aluminium with diameter of1mm and wall of pure graphite with thickness of 0.75mm. Calculated exposure rate constants for 60 Co, 22 Na and 111 In at 20 to 300cm from the source ranged from 33.45 to 0.16 mR/(mCi.h), 29.12 to 0.10 mR/(mCi.h) and 8.73 to 0.03 mR/(mCi.h) respectively which show a decreasing trend. Comparison of our results with other studies show that there are good agreement for 60 Co and 22 Na; the present values for exposure rate constant for 111 In was higher than previous reports.