Study of Self-Absorption in Gamma-Ray Spectroscopy of Environmental Samples

HPGe detector has been simulated by using MCNP code, and the detector response has been determined. Monte Carlo simulations have been performed for different elemental composition and density as environmental Marinelli samples (z =10-90, ρ = 0.8-2 g/cm3). Likewise, more experiments were carried out in the laboratory scale using five samples with different self-absorption albeit with the same detector described previously. The effects of source elemental composition and density on the self-absorption in gamma-ray spectroscopy of environmental Marinelli samples are discussed. For both cases of experimental and simulated studies a surface plot of the efficiency vs gamma-ray energy and sample density has been calculated for the said detector. By comparing the results upon applying, two methods show that the simulation method has been successful leading to efficiency as a function of both gamma-ray energy and sample density. The same surface can be used to derive an efficiency curve for any sample density within the calibrated range of densities. Also, it is possible to use this three-dimensional curve to reduce the number of calibration standards of different required densities, where it leads to reducing the laboratory operating costs. The results showed that the sample density was more important than the composition in self-absorption problem. In addition, the effects of the sample density on self-absorption in all range of the energy under the study are visible, but the chemical composition effects appear only for the E<400 keV condition.