Effective atomic numbers for photon energy absorption and energy dependence of some thermoluminescent dosimetric compounds

Abstract

Effective atomic numbers for photon energy absorption and energy dependence (ED) of some selected pure thermoluminescent dosimetric (TLD) compounds such as LiF, CaCO 3, CaSO 4, CaSO 4 · 2H 2O, CdSO 4, SrSO 4 and BaSO 4 have been calculated in the energy region of 1 keV to 20 MeV. The more commonly used empirical formula for calculating the measure of ED in the energy region of interest in TL dosimeters through effective atomic numbers predicts higher values for all the materials studied compared to those ones calculated by direct method and by as much as 20% for SrSO 4. A modified formula fitted to directly calculated effective atomic number data gives better agreement within a maximum deviation of ±3.94% for all the TLD materials studied. Overall the effective atomic number varies linearly with ED in the photon energy range of 1 keV to 20 MeV and thereby confirming the validity of a more commonly employed method of using the effective atomic number to calculate the measure of the ED in TL dosimetry. Significant differences exist between the effective atomic numbers for photon interaction and photon energy absorption in the energy region 20–150 keV for LiF, 2–300 keV region for CaCO 3, CaSO 4 and CaSO 4 · 2H 2O, 3–1000 keV region for CdSO 4, 20–600 keV for SrSO 4 and 1–1000 keV for BaSO 4. The effect of absorption edge on effective atomic numbers and ED, their variation with photon energy and the possibility of defining two set values of these parameters below the K-absorption edge of high- Z element present in the TLD material are discussed.