A new and general efficiency calibration methodology for Ge detectors using LabSOCS

Abstract

The measurement of natural and artificial radionuclides is really needed in many research fields such as radioecology, radiobiology, radiological protection, medical physics and environmental radioactivity. The gamma-ray spectrometry using Ge detectors has become one the most employed radiometric techniques, where a proper efficiency calibration based on the full-energy peak efficiency (FEPE) is essential for the measurement of radionuclides. To obtain the FEPEs, the use of simulation programs, especially LabSOCS, has become generalized. However, when obtaining the FEPEs by LabSOCS, the reproduction of each geometry is usually time consuming. Moreover, when using LabSOCS, there are important limitations regarding the chemical composition that is possible to specify for each sample. For these previous reasons, this study aims to develop a novel and general efficiency calibration methodology for Ge detectors using LabSOCS for cylindrical geometries. For this, a general analytical function was obtained for the simulated FEPEs for the calibration sample (${\epsilon }_c$, water in this case) depending on the sample thickness (h), internal geometry diameter (d) and gamma emission energy (E_γ), where a multiple fitting procedure was developed consisting in three steps: 1. FEPEs vs h (h = 5–50 mm), fixing d and E_γ, obtaining the parameters p_h from these fits, 2. p_h vs d (d = 7–70 mm), fixing E_γ, obtaining p_d, and 3. p_d vs E_γ (E_γ = 46–1460 keV), obtaining $p_{E_{\gamma }}$. For all the fits, the obtained ${\chi }_R^2$ values were less than the critical ${\chi }_R^2$ ones. Then, the general ${\epsilon }_c\left(h,d,E_{\gamma }\right)$ function was also obtained for any problem sample ($\epsilon$) using an analytical function of the self-attenuation correction factor (f_a). The applicability range of the f_a function was comprehensively analyzed for a wide range of chemical compositions, apparent densities (ρ), h, d, and E_γ, comparing the results obtained by the f_a function and LabSOCS, finding that for 7 mm $\le$ d $\le$ 35 mm, the f_a function properly works for h < 25 mm for any problem sample, while for d > 35 mm, it properly does for h $\le$ 25 mm. Moreover, the general $\epsilon$ function obtained in this study was externally and internally validated using reference and non-reference materials for a wide range of chemical compositions, ρ, h, d, and E_γ for both natural and artificial radionuclides.