Investigating the Effect of Matrices and Densities on the Efficiency of HPGe Gamma Spectroscopy Using MCNP (original) (raw)
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Nukleonika, 2017
A methodology to determine the full energy peak efficiency (FEPE) for precise gamma spectrometry measurements of environmental samples with high-purity germanium (HPGe) detector, valid when this efficiency depends on the energy of the radiation E, the height of the cylindrical sample H, and its density ρ, is introduced. The methodology consists of an initial calibration as a function of E and H and the application of a self-attenuation factor, depending on the density of the sample ρ, in order to correct for the different attenuation of the generic sample in relation to the measured standard. The obtained efficiency can be used in the whole range of interest studied, E = 120–2000 keV, H = 1–5 cm, and ρ = 0.8–1.7 g/cm3, being its uncertainty below 5%. The efficiency has been checked by the measurement of standards, resulting in a good agreement between experimental and expected activities. The described methodology can be extended to similar situations when samples show geometric and...
To obtain high quality of results in gamma spectrometry, it is necessary to select the best HPGe detector for particular measurements, to calibrate energy and efficiency of gamma detector as accurate as possible. To achieve this aim, the convenient detector model and gamma source can be very useful. The purpose of this study was to evaluate the soil specific activity using two HPGe model (BEGe-6530 and GC0818-7600SL) by comparing the results of the two detectors and the technics used according to the detector type. The relative uncertainty activity concentration was calculated for 226Ra, 232Th and 40K. For broad energy germanium detector, BEGe-6530, the relative uncertainty concentration ranged from 2.85 to 3.09% with a mean of 2.99% for 226Ra, from 2.29 to 2.49% with a means of 2.36% for 232Th and from 3.47 to 22.37% with a mean of 12.52% for 40K. For GC0818-7600SL detector, it was ranged from 10.45 to 25.55% with a mean of 17.10% for 226Ra, from 2.54 to 3.56% with a means of 3.10% for 232Th and from 3.42 to 7.65% with a mean of 5.58% for 40K. The average report between GC0818-7600SL model and BEGe-6530 model was calculated and showed the mean value of 3.36. The main study was based on the following points: •Determination of The relative uncertainty activity concentration of 226Ra, 232Th, and 40K •Determination of the relative uncertainty related to the radium equivalent activity to compare the performance of the two detection systems •Proved that the activity concentration determination in gamma spectrometry depended on the energy range emitted by a radionuclide. This study showed that the standard deviation measurement was less important to the result realized with BEGe-6530 HPGe model. Our findings were demonstrated that the results of the Broad Energy Germanium detector were more reliable.
Low-level gamma-ray spectrometry for environmental samples
Journal of Radioanalytical and Nuclear Chemistry, 2008
Low-level gamma-ray spectrometry with large volume HPGe detectors has been widely used in analysis of environmental radionuclides. The reasons are excellent energy resolution and high efficiency that permits selective and non-destructive analyses of several radionuclides in composite samples. Although the most effective way of increasing the sensitivity of a gamma-ray spectrometer is to increase counting efficiency and the amount of the sample, very often the only possible way is to decrease the detector's background. The typical background components of a low-level HPGe detector, not situated deep underground, are cosmic radiation (cosmic muons, neutrons and activation products), radioactivity of construction materials, radon and its progenies. A review of Monte Carlo simulations of background components of HPGe detectors, and their characteristics in coincidence and anti-Compton mode of operation are presented and discussed.
Applied Radiation and Isotopes, 2004
Accurate determination of the massic activity of gamma-emitting radionuclides in environmental samples, particularly sediments and soils, cannot be achieved without taking into account sample self-absorption. The extent of self-absorption in the sample will depend on a number of factors including sample composition, density, sample size and gamma-ray energy. The preferred method for correcting for this effect is to use spiked or natural matrix reference materials that match each sample type to be analysed. However, for laboratories that must measure a wide variety of sample matrices this method is too costly and time-consuming. Another technique commonly used is to make direct gamma-ray transmission measurements for each sample. This method, while more practical, still requires a minimum of three measurements to be made for each sample analysed. A more convenient method is to prepare sets of gammaabsorption curves. This approach involves making a series of direct transmission measurements for samples of varying densities but similar type. Sets of matching samples, both spiked and unspiked, were prepared and density correction factors determined using the direct transmission method and the spiked sample approach. It was found that, for soil and sediment samples, these two methods typically differed by 5-9% for higher energy gamma rays and by 12-15% for the 59.54 keV 241 Am peak. Gamma-absorption curves were also derived and, for the admittedly limited dataset, 95% confidence intervals of 77% for the curve generated using the spiked samples method were obtained. r
Using MCNP Simulation for Self-absorption Correction in HPGe Spectrometry of Soil Samples
Iranian Journal of Science and Technology, Transactions A: Science, 2019
The self-attenuation correction coefficients (C sa) for 137 Cs counting in twelve soil samples were determined by MCNP simulation of a high-purity germanium detector. The correction coefficients were defined as the simulation and experimental efficiency ratio for gamma radiation with 661.66 keV. The experimental efficiency of the detector for 661.66 keV of gamma energy in soil samples was obtained using the IAEA reference materials. The exact gamma radiation efficiency for soil samples was calculated on the correct height and soil density using the MCNPX simulation code. The result of the measurements, including the self-attenuation correction coefficient, was compared with the given value and indicates an increase in accuracy.
Improvement of in-situ gamma spectrometry methods by Monte-Carlo simulations
Journal of Environmental Radioactivity
Performing in-situ measurements of gamma radiation originating from soil requires adequate detection efficiency curves, which can be obtained by Monte-Carlo simulations. In simulations, soil density of 1.046 g/cm 3 was used, with the following elemental composition of soil in which gamma radiation was generated: O-47%, Si −35%, Al-8%, Fe-3.9%, C-2.1%, Ca-1.4%, K-1.3%, N-0.6%, Mg-0.6%, N-0.1%. Soil matrix was represented by cylindrical volume of 1.5 m diameter and 0.5m thickness, while germanium detector was placed at 1 m height above the soil. The simulated gamma spectrum, originated from K-40, as well as from members of Th-232 chain, and daughters of Ra-226, was obtained. Homogeneous distribution of various radionuclides (Ra-226, Th-232, K-40) in soil matrix is considered in this work. Gamma spectra obtained in simulations were analyzed, and together with simulated detection efficiency data they provide comparison with real experimental measurements and practical application of results derived by Monte-Carlo simulations. As a result of this work, the corresponding detection efficiency curve for HPGe detector was obtained, which can be applied for in-situ measurements of radionuclide concentration in soil, assuming uniform radionuclide distribution. In order to validate our simulation results regarding detection efficiency, we performed in-situ measurements of soil radioactivity and compared the obtained activity concentrations with laboratory measurements. We found a good agreement, within activity concentration uncertainty, between in-situ measurement results and average values of activity concentrations obtained by laboratory measurements. 1 10 sr) in simulations, which can be achieved in practice by portable modular shield, mounted around the portable detector. HPGe detector crystal had 60 mm diameter and 50 mm height (Fig. 2).
2011
Gamma-ray spectrometry is widely used for the determination of radionuclide activity in nature. This technique allows to carry out measurements without the routinely used radiochemical methods and multielemental analysis [1, 10, 12, 17, 26, 27, 29]. In order to obtain correct results, voluminal samples shall be counted under the same measuring conditions (geometric setup, chemical composition, density) as those under which the γ-spectrometer has been calibrated. However, in many cases this is not possible, above all when we want to measure environmental samples. The latter have different chemical compositions and density. This is the reason why attenuation correction is an important factor. In the last three decades a number of ways of comprehensive calibration of Ge detectors were developed, especially concerning measurements of environmental volume samples. Generally, we have two approaches: mathematical [9, 11, 13–15, 23, 28, 30] and experimental [2–7, 16, 18–22, 24, 25]. Accurat...
Journal of Radioanalytical and Nuclear Chemistry, 2019
In this work the efficiency calibration curves for a HPGe gamma detector were obtained from soil standards prepared in our laboratory using typical Argentine regional soils. They were made in pot and Petri dish geometries, for different soil granulometries, by using two mixed nuclide reference solutions manufactured by Eckert & Ziegler and provided by the IAEA. The efficiency curves obtained were tested with the reference materials IAEA-375, IAEA-447, CNEA-81-11 as well as the soil sample used in the IAEA-2013 proficiency test. The results allow to improve the quality in the analytical measurements on the content of radionuclides in local soils.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2018
The aim of this paper is to characterize two HPGe gamma-ray detectors used in two different laboratories for environmental radioactivity measurements, so as to perform efficiency calibrations by means of Monte Carlo Simulation. To achieve such an aim, methodologies developed in previous papers have been applied, based on the automatic optimization of the model of detector, so that the differences between computational and reference FEPEs are minimized. In this work, such reference FEPEs have been obtained experimentally from several measurements of the IAEA RGU-1 reference material for specific source-detector arrangements. The models of both detectors built through these methodologies have been validated by comparing with experimental results for several reference materials and different measurement geometries, showing deviations below 10% in most cases.
Monte-Carlo modeling allows calculating the detector efficiency in gamma spectrometry of environmental samples with taking into consideration both the photon selfabsorption in sample itself and absorption in all other materials between the sample and the detector's active part. In this paper, the peak efficiencies of the Hp Ge detector (GMX) for gammas at various energies (emitted isotropically from the standard disk source and volumetric source -environmental sample, in which the different radionuclides are present) are calculated based on MCNP4C2-Monte-Carlo multi-purpose radiation transport code system developed in the Los-Alamos laboratory, U.S.A. The obtained calculating results are compared with the experimentally measured data and a good agreement between them is shown out.