Comparison of conversion factor methods in spectrometric dosimetry systems based on NaI(Tl) scintillation detectors

To monitor personal safety in the fields of biomedical and health physics, it is necessary to be aware of radiation doses to protect the health and safety of persons. Radiation protection quantities such as air kerma, ambient dose equivalent, and exposure dose rate are obtained by the measured spectrum to determine energy-dependent conversion coefficients/factors. This study aims to obtain and compare an ambient dose equivalent to H∗(۱۰) from the measured gamma-ray spectra by the NaI(Tl) scintillation detector using two various methods. The first method, which is based on the detector response function to find the conversion function, is called the G(E) method. The second method is subdividing the measured gamma-ray spectra into the multiple energy bins, and then obtaining the ambient dose equivalent by using conversion coefficient functions (ω(E)), which were determined by the conversion coefficients (ωi) of each energy bin for three energy intervals of ≤۱۸۵ keV, ۱۸۵ to ۸۵۰ keV, and ≥۸۵۰ keV. To calculate the detector response matrix and the conversion coefficients of each region of energy, the Monte Carlo simulation code was used for the quasi-mono energetic gamma radiation sources and the synthetic spectra. The results indicate that using the technique based on subdividing the measured spectrum into multiple energy bins helps to avoid the inverse detector response matrix dimension limitations that occur in the G(E) method and also have a lower error percentage in the dose quantity calculation. Consequently, NaI(Tl) scintillation detector has an excellent potential to replace the classical dose rate instruments, i.e. Geiger-Muller, for the early warning of environmental radiation monitoring.

Keywords:

Detection , Monte-Carlo simulation , Ambient dose , Spectro-Dosimeter method , Energy-dependent conversion coefficients