Monte Carlo calculation of the sensitivity of a commercial dose calibrator to gamma and beta radiation

Abstract

The detection process used in a commercial dose calibrator was modeled using the GEANT 3 Monte Carlo code. Dose calibrator efficiency for gamma and beta emitters, and the response to monoenergetic photons and electrons was calculated. The model shows that beta emitters below 2.5 MeV deposit energy indirectly in the detector through bremsstrahlung produced in the chamber wall or in the source itself. Higher energy beta emitters (E > 2.5 MeV) deposit energy directly in the chamber sensitive volume, and dose calibrator sensitivity increases abruptly for these radionuclides. The Monte Carlo calculations were compared with gamma and beta emitter measurements. The calculations show that the variation in dose calibrator efficiency with measuring conditions (source volume, container diameter, container wall thickness and material, position of the source within the calibrator) is relatively small and can be considered insignificant for routine measurement applications. However, dose calibrator efficiency depends strongly on the inner-wall thickness of the detector.

Usefulness of specific calibration coefficients for gamma‐emitting sources measured by radionuclide calibrators in nuclear medicine

“…In this work, we used the version 4.8 of the Monte Carlo code Geant. 19 The main improvements of this version compared to version 3 that we used in our previous publication 20 are the lowering of the cut thresholds, which particularly affects the low density materials such as the interior of the chamber, and a better treatment of the ionization process, with the so-called "LowEm" package.…”

“…At less than about 3 MeV, the electrons only deposit their energy through the bremsstrahlung produced in the source or the instrument surroundings. 20 At 4 MeV, the sensitivity suddenly increases because the electrons start to have energies sufficiently high enough to interact directly with the sensitive volume. Figure 3 shows the relative sensitivity of the instrument for each container of interest under standard-filling conditions averaged for different ranges of photon energies.…”

Calibration of an HPGe detector and self-attenuation correction for 210Pb: Verification by alpha spectrometry of 210Po in environmental samples

“…Below this threshold, the particles are stopped and their energy is considered as locally deposited. Previous studies performed by the authors with electrons and photons in an energy range between 10 and 3 MeV involved simulations, and experimental results have been used as a code validation for the present work [16,17,19,20]. The entire stochastic emission process, beginning with the decay scheme of the 210 Pb, was modelled using an internal code named Sch2for [17].…”

Monte Carlo Simulation of a Clearance Box Monitor Used for Nuclear Power Plant Decommissioning

“…The code has been previously validated by the authors for photons, electrons, and positrons in an energy range between 50 keV and 3 MeV (Laedermann et al 2004). It models the following photon interactions: classical diffusion, Compton scattering, pair production, and photoelectric absorption as well as the production of Auger electrons and characteristic x rays.…”