Application of the Monte Carlo method for the efficiency calibration of CsI and NaI detectors for gamma-ray measurements from terrestrial samples

Gamma-ray measurements in terrestrial/environmental samples require the use of high efficient detectors because of the low level of the radionuclide activity concentrations in the samples; thus scintillators are suitable for this purpose. Two scintillation detectors were studied in this work; CsI(Tl) and NaI(Tl) with identical size for measurement of terrestrial samples for performance study.This work describes a Monte Carlo method for making the full-energy efficiency calibration curves for both detectors using gamma-ray energies associated with the decay of naturally occurring radionuclides 137Cs (661 keV), 40K (1460 keV), 238U (214Bi, 1764 keV) and 232Th (208Tl, 2614 keV), which are found in terrestrial samples. The magnitude of the coincidence summing effect occurring for the 2614 keV emission of 208Tl is assessed by simulation.The method provides an efficient tool to make the full-energy efficiency calibration curve for scintillation detectors for any samples geometry and volume in order to determine accurate activity concentrations in terrestrial samples.

► CsI (Tl) and NaI (Tl) detectors were studied for themeasurement of terrestrial samples.
► Monte Carlo method was used for efficiency calibration using natural gamma emitting terrestrial radionuclides.
► The coincidence summing effect occurring for the 2614 keV emission of 208Tl is assessed by simulation.