Full Energy Peak Efficiency Calibration Research Articles

A comparative study on full-energy peak efficiency calibration methods for HPGe detector: Virtual point detector, curve fitting, and machine learning models

This paper presents a comparative study of three models including virtual point detector (VPD), curve fitting (CF), and machine learning (ML) in determining the full-energy peak efficiency (FEPE) of HPGe (High Purity Germanium) detector with different energy point sources located on the symmetric axis of the detector at different source-to-detector distances. Firstly, the FEPEs were determined for energies spanning from 40 keV to 2500 keV and distances ranging from 1.88 cm to 25.68 cm, utilizing the MCNP6 code. These simulated data were then used to construct the VPD, CF, and ML models. The accuracy of each model was assessed by comparing its efficiency calibration results against experimental data. In the VPD and CF models, the obtained results are fairly accurate for energies above 240 keV, with relative deviations between calculated and experimental FEPEs (RDExp/Cal) of less than 4 %. However, for energies below 240 keV and at small source-to-detector distances, the RDExp/Cal is quite large, reaching up to 10 % with the VPD model and 5 % with the CF model. In the ML model, the maximum difference between the predicted and experimental FEPEs is 2.4 % for the whole investigated energy range and distances. Our study shows that the ML model outperforms VPD and CF models in terms of accuracy, particularly in situations with low energies (below 240 keV) and at positions close to the detector surface, where the VPD and CF models often give results with low accuracy. Therefore, the ML model can be considered a useful and highly reliable computational solution for calculating the FEPE of the HPGe detector.

Utilization of different radionuclides for high-energy extended efficiency calibration of a HPGe for improved determination of calcium and sulfur using k0-INAA

The present study reports on the performance of three reactor-produced radionuclides (24Na, 56Mn, and 72Ga) and one accelerator-produced radionuclide (56Co) for extending the full-energy peak efficiency calibration of a coaxial HPGe detector up to ~ 3100 keV at different detector to source distances. The differences between the efficiency curves obtained with and without the use of high-energy gamma emitters radionuclides have a considerable impact on the accuracy of the Na, Ca, and S determination by the k0-INAA as evidenced by analysis results of reference materials. The results revealed that 24Na is the most suitable radionuclide for high-energy efficiency calibration due to its reasonable availability, low production cost, simple decay scheme, and well-defined decay properties.

Study of the effect of photon self-absorption on the detection efficiency of HPGe detector in measurements of an activated uranium sample

The photon self-absorption effect of uranium on the full-energy peak (FEP) efficiency calibration of high purity germanium (HPGe) detector was studied as a function of energy using an activated uranium sample has a thickness of 1 mm. The absolute efficiencies of the detector were obtained with the use of gamma standard sources and gamma rays of radionuclides created by irradiating the uranium sample with secondary neutrons. The measurements were carried out with the use of a Planar HPGe detector. MCNP simulation code was used to verify the experimental results. The comparison of the empirical results with the simulation results showed a good agreement. To interpret the efficiencies, the reaction rates were calculated using two methods: (1) - the use of the efficiency curve from the standard sources combined with the self-absorption correction of the uranium material and (2) - the use of the efficiency curve obtained from gamma rays in the sample.

Towards the Reliability Check of Complementary Methods for the Precise Estimation of Peak Efficiency of a Long Run Used Germanium Detector in Low Activity Environmental Measurements

The gamma-ray spectrometry using long run used hyper pure germanium (HPGe) detector needs a stringent full energy peak (FEP) efficiency calibration for environmental radioactivity measurements. The FEP efficiency calibration was carried out using the complementary methods like analytical estimations and Monte Carlo (MC) simulations. In our work, for the analytical estimations, the relative deviation of the theoretical results with that of experimental FEP efficiency was found to be less than 6%. However, in the case of MC methodologies, an overall estimated standard deviation of 5% could be achievable only with the optimized geometry of the long run used germanium detector for low-activity environmental measurements.

Performance of various mathematical functions for the in-situ relative detector efficiency towards its applicability for k0 IM-NAA

The in-situ relative detection efficiency strongly influences the characteristics of the k0-based internal monostandard neutron activation analysis (IM-NAA). In the present work, various mathematical functions were explored for the establishment of in-situ relative detector efficiency calibration and compared their performance based on the reduced chi-square (χ2) values. Among the various mathematical functions, the polynomial logarithm with 6th order was found to be associated with the minimum mean standard deviation for the experimental data and the lowest value of reduced χ2 after carrying out multiple iterations using Nelder–Mead algorithm. Quality assurance of the function was tested by carrying out elemental quantification of the NIST SRM 1633b coal fly ash. Gamma energies of the activation products, 152mEu, 59Fe, 140La, 24Na and 46Sc of the irradiated NIST standard were used for the in-situ relative full energy peak efficiency calibration of 30% HPGe detector. The sample was counted for different time intervals for the complete profiling of the elements present in the NIST SRM. The deviations for most of the elements were found to be within ±5% with respect to the certified values and ξ-score values were within ±2, demonstrating its better accuracy. This method was also applied satisfactorily to profile the elemental concentrations of alloy materials used in a thermal sensor guide tube of the steam generator in a test reactor.

Development of a semi-empirical calibration method by using a LaBr3(Ce) scintillation detector for NORM samples analyses

In this study, a semi-empirical calibration method for NORM samples measurement by using a LaBr3(Ce) scintillator was developed based on a combination of experimental gamma spectrometry measurements and MCNP-X simulations. The aim of this work is to provide us with full energy peak efficiency calibration curves in a wide photon energy range which is of particular importance when selected photon energies of 234Th, 214Pb, 214Bi, 228Ac, 208Tl and 226Ra are to be measured with accuracy.

Validation of Full Energy Peak Efficiency Calibration of HPGe Gamma-Ray Spectrometer Using Empirical Efficiency Curve Transfer

Validation of Full Energy Peak Efficiency Calibration of HPGe Gamma-Ray Spectrometer Using Empirical Efficiency Curve Transfer

Measurement of the absolute gamma emission intensities from the decay of Th-229 in equilibrium with progeny

There are few long-lived radionuclides yielding high intensity gamma-rays emission with energies ranging from 100 keV to 500 keV that can be applied as radioactive gamma standard to calibrate HPGe detectors. Furthermore, this energy range represents the main emitted energies of the majority of radionuclides used in nuclear medicine. The Brazilian National Laboratory for Ionizing Radiation Metrology (LNMRI/IRD/CNEN) has attempted to identify radionuclides that have the potential to be used as a calibration source due to their long half-life as well as their emission spectrum. Hence, LNMRI promotes standardization studies of gamma-emitting radionuclides that meet these criteria on order to disseminate them. Thorium-229, with its well-defined energies and relatively high intensities, is one such candidate radionuclide for the energy and full-energy peak efficiency calibration of high-purity gamma spectrometers. Thorium-229 was standardized by the method of 4παβ(LS)-γ(NaI(Tl)) live timed anticoincidence counting. The emission intensities of gamma-rays associated with the decay of 229Th have been determined by HPGe gamma ray spectrometry with accuracy and precision. The results are in agreement with current literature data.

A hybrid analytical–numerical method for full energy peak efficiency calibration of a NaI detector

A hybrid analytical–numerical method is proposed to determine the Full Energy Peak Efficiency (FEPE) of a NaI bare crystal for a point γ-source in the energy range 48–2040 keV. The efficiency is calculated at all possible source locations with respect to the detector and at a maximum Source-to-Detector (S–D) distance of 50 cm. The method combines an analytical formula used for total efficiency calculation with numerically calculated Peak-to-Total (P/T) ratios. The FEPE efficiencies are calculated by integrating the combined analytical formula. A computer code is written using the C programming language to solve the integration using Simpson’s rule. The calculated values of the FEPE are found to be in agreement with these calculated using the Monte Carlo (MC) method with a maximum relative difference of about 2.5%. The main advantage of the proposed method is the extremely reduced runtime of calculation in comparison with the MC method.

Full energy peak efficiency calibration for the assay of large volume radioactive waste drums in a segmented gamma scanner

Large volume radioactive waste drums with low/intermediate level of alpha activity, generated in radiochemical laboratories, are in general screened for special nuclear materials (SNM) in a segmented gamma scanner (SGS) before disposal. The assay methodology traditionally requires a standard drum of identical geometry and thereby making the procedure relying on the availability of a true standard, which is often difficult to organize. Here, we report a non-conventional absolute segmented gamma scanning (ASGS) methodology for the assay of 200 L waste drums, avoiding the use of a standard drum. The present analysis employ the full energy peak (FEP) efficiency, ingeniously determined using a standard 152Eu point source. From combined experiment and Monte Carlo simulation, it has been established that, the FEP efficiencies of the detector for a 200 L cylindrical sample can be well reproduced using a point source. While verifying the applicability of the point source FEP efficiencies for the assay of plutonium in 200 L drums, an energy dependent bias has been seen, which confirms the presence of lump attenuation in addition to the general matrix attenuation. An infinite energy extrapolation of apparent mass approach has been adopted for the assay of large volume waste drums which takes care of the gamma-ray attenuation from all sources that is otherwise difficult to correct for in a sample drum of unknown history.

Influence of angular correlations on the full energy peak efficiency calibration using the sum peak method

To investigate the accuracy of the calibration of the HPGe detectors using an uncalibrated complex gamma cascade emitting source and the sum-peak method, Monte Carlo simulations were conducted. It was shown that accuracy below 5% is achievable for a 133Ba source, only if the spectral data are corrected for angular correlations even at short distances from the detector endcap.

Intercomparison of full energy peak efficiency curves for an HPGe detector using MCNP6 and GEANT4

This work is focused on studying the capabilities of different Monte Carlo tools to complement the Full Energy Peak Efficiency (FEPE) calibration procedures of the Environmental Radioactivity Laboratory of the Universitat Politècnica de València, UPV. In this frame, detailed models of a High Purity Germanium detector have been implemented using MCNP6 and GEANT4. Accordingly, an inter-comparison with experimental values ensures the model validation and improves the analysis of the physics phenomena involved. The validation of the models is determined by a quantitative comparison between the simulated and the measured efficiencies over the energy range under study (59.54–1836.01 keV). The results show discrepancies between both Monte Carlo tools for 139Ce, 88Y and 60Co as GEANT4 is able to simulate the coincidence summing effect of these radionuclides.

Full-Energy Peak Efficiency Calibration of a Metallic Magnetic Calorimeter Detector for Photon Spectrometry Below 100 keV

Knowledge of absolute emission intensities of X-ray lines below 100 keV is limited or missing. An absolute determination of these intensities necessitates a high-resolution spectrometer with an accurate efficiency calibration. In this work, we will show and discuss the FEP efficiency calibration of a MMC detector combining a measurement of a standard source with Monte Carlo simulations using the code PENELOPE-2014. The simulated efficiency detection successfully interpolated the experimental efficiency values.

Coincidence summing corrections for a clover detector

The true coincidence summing effect on the full energy peak efficiency calibration of a clover HPGe detector for point sources has been determined as a function of sample-to-detector distance using mono-energetic and multi-energetic gamma ray sources. The coincidence summing effect has been observed to increase at closer distances with the correction factors as high as 1.25 at closest distance studied. The correction factors for the total and the photopeak efficiencies have been obtained using the analytical method. The clover detector response has been simulated using MCNP code, taking care of the bevels and the flat surfaces of the clover detector. The geometry of the clover detector has been optimized to match the experimental and the theoretical efficiencies. The true coincidence summing correction factors (kTCS) have also been experimentally obtained by taking the ratio of corresponding mono-energetic extrapolated efficiencies to multi-energetic efficiencies. The kTCS obtained from analytical method has been found to match with the experimental kTCS with the simulated values within 1–5%.

Full Energy Peak Efficiency Calibration and Efficiency Transfer to ETNA in Gamma-ray Spectrometry

Accurate determination of the radionuclide concentration in environmental sample depends directly on the accurate efficiency calibration in gamma ray spectrometry. The detection efficiency may vary due to some factors (density, sample filling height, matrix, measurement geometry, self-absorption, detection system, etc.) for voluminous samples. Some studies has been conducted in this work and presented in here. The efficiency calibration was performed for two HPGe detectors (relative efficiency of 20% and 40%), using samples (STDMS, STDMP, STDMPF, STDMRL, STDB, STDMC, & STDMG) of various densities (0.55 to 1.59 g/cm 3 ) in cylindrical containers (V=240 cm 3 ) for the gamma ray energy range of 121 keV to 2614 keV. Secondary reference material was prepared by using the standard reference liquid source 152 Eu. From the experimental result it can be seen that efficiency value is inversely proportional to the gamma ray energy. For lower gamma energies of selected nuclide, the efficiency value comparatively higher than the high energies of that nuclide. Efficiency value also varies with filling height of sample. Computer software ETNA was used for the efficiency transfer measurements of three samples (STDMP, STDMPF, & STDMRL) for the configuration of 20% relative efficiency detector. The efficiency value obtained from ETNA was compared with analytical efficiency value. Approximately 2.2% to 15.5% variation was found within the two systems. From the result it can be said that at the initial stage this kind of technical approach is not convenient for the environmental sample measuring laboratory due to the availability of input data for running the ETNA.

True coincidence summing corrections in point and extended sources

The true coincidence summing (TCS) effect on the full energy peak (FEP) efficiency calibration of an HPGe detector has been studied as a function of sample-to-detector distance using multi-gamma sources. Analytical method has been used to calculate coincidence correction factors for 152Eu, 133Ba, 134Cs and 60Co for point and extended source geometry at close sample-to-detector distance. Peak and total efficiencies required for this method have been obtained by using MCNP code by using the optimized detector geometry. The correction factors have also been obtained experimentally. The analytical and the experimental correction factors have been found to match within 1–5%. The method has been applied to obtain the activity of the radionuclides (106Ru, 125Sb, 134Cs and 144Ce) present in a fission product sample.

Calibration of an in-situ BEGe detector using semi-empirical and Monte Carlo techniques

In the case of a nuclear or radiological accident a rapid estimation of the qualitative and quantitative characteristics of the potential radioactive pollution is needed. For aerial releases the radioactive pollutants are finally deposited on the ground forming a surface source. In this case, in-situ γ-ray spectrometry is a powerful tool for the determination of ground pollution. In this work, the procedure followed at the Nuclear Engineering Department of the National Technical University of Athens (NED-NTUA) for the calibration of an in-situ Broad Energy Germanium (BEGe) detector, for the determination of gamma-emitting radionuclides deposited on the ground surface, is presented. BEGe detectors due to their technical characteristics are suitable for the analysis of photons in a wide energy region. Two different techniques were applied for the full-energy peak efficiency calibration of the BEGe detector in the energy region 60-1600 keV: Full-energy peak efficiencies determined using the two methods agree within statistical uncertainties.

Full energy peak efficiency calibration of HPGe detector for point and extended sources using Monte Carlo code

Monte Carlo simulation is important to get efficiencies for cases where the experimental efficiencies are difficult to get such as for samples with nonstandard geometries and for large samples. In this paper, efficiency of the HPGe detector, routinely used in our lab for a variety of samples, has been computed for point source geometry and its parameters has been optimized to match MCNP and experimental efficiencies within 5% at different sample to detector distances. This optimized geometry was then validated by efficiency transfer to other geometries.

Measurements of high-energy [formula omitted]-rays with [formula omitted] detectors

The full-energy peak efficiency calibration and the energy resolution measurements of the 2 in . × 2 in . LaBr 3 γ -ray detector are presented for γ -ray energies in the 700 keV–17.6 MeV range. Measurements were done using a combination of proton-capture nuclear reactions on Al 27 , Na 23 , K 39 , Li 7 and B 11 for high-energy γ -rays, and radioactive sources such as Co 60 and Eu 152 for the lowest energies. At high energies, two γ -rays in a cascade from proton resonance capture were employed using Al, Na 2 WO 4 , K 2 SO 4 and LiBO 2 targets. The obtained results were compared to the simulations performed using a GEANT4 code.

Development and implementation of k0-INAA standardization at 10 MW Pakistan research reactor-1

The k o -method has been developed for 10 MW Pakistan Research Reactor (PARR-1). It involved the full energy peak efficiency calibration of HPGe detector for different counting geometries and characterization of neutron flux at three irradiation channels. Neutron flux was characterized for thermal to epithermal flux ratio, epithermal flux shape factor, modified spectral index, Westcott's g-factor and fast flux. The method was validated by analyzing IAEA-SL1 (lake sediment) and NIST-SRM-1572 (citrus leaves). All calculations were performed in Excel. The results revealed most of the elements with good accuracy.