Application of the Monte-Carlo Method for Calibration of a Gamma-ray Scintillation Spectrometer

Purpose: To develop a method for calibration of a gamma-ray scintillation spectrometer using the Monte Carlo method.

Material and methods: The subject of the study was a gamma-ray spectrometer designed to measure the energy distribution (spectrum) and determine the activity of gamma-emitting radionuclides. Experimental studies were carried out with a set of exemplary measures of special-purpose activity with radionuclides ²⁴¹Am, ¹⁵²Eu, ⁶⁰Co and ¹³⁷Cs uniformly deposited on an ion exchange resin. Calibration of the spectrometer was carried out using the MCC 3D program (Monte Carlo Calculations 3D), modeling of the hardware spectrum was performed using the MCA program (MultiChannel Analyzer).

Results: The comparison of experimental and simulated spectra was carried out in the following energy intervals: the interval corresponding to the total peak of total absorption (PTA) for gamma energy lines 1173.2 keV and 1332.5 keV for ⁶⁰Co and PTA for gamma energy line 661.7 keV for ¹³⁷Cs; intervals corresponding to Compton scattering in the angle range (30–60)°, (60–90)° and (90–180)° (for the ⁶⁰Co, the average gamma radiation energy of 1252.9 keV was considered); the interval corresponding to multiple scattering with an energy above 100 keV. It was found that the largest deviation of the simulated spectrum from the experimental one is 12 % for the interval corresponding to multiple scattering, which indicates the possibility of spectrum identity. This assumption was verified for each energy interval using the Pearson consensus criterion. A maximum value of χ² equal to 6.6 was obtained for the energy interval corresponding to Compton scattering in the angle range (60–90)°, which indicates the acceptability of the hypothesis of the identity of the experimental and simulated spectra. Validation of the proposed method showed that the discrepancy between the calculated and passport activity of the sample was no more than 13 %, which indicates the possibility of using the method for calibration of the gamma spectrometer. The dependences of the efficiency of registration in the PTA on the density of the counting sample are calculated using simulated hardware spectra of single activity.

Conclusion: The proposed method makes it possible to calibrate the spectrometer to calculate the specific activity in samples at various densities and energies using spectrometric equipment equipped with inorganic scintillation crystals.