True Coincidence Summing Correction Research Articles

An operational approach for accurate 177Lu and 177mLu activity quantifications to comply with the environmental release criteria: the role of GEANT4 for efficiency curve and True Coincidence Summing effect estimation

The increasing use of 177Lu-labelled agents for targeted radionuclide cancer therapy highlights the radiation protection challenges in the management of radioactive waste due to 177mLu impurities. To ensure safe disposal, compliance with clearance criteria must be verified using calibrated systems, such as Hyper Pure Germanium (HPGe) spectrometers. This work aims to validate a customized GEANT4 model of our HPGe system in Marinelli beaker geometry to propose an operational approach properly quantifying 177Lu and 177mLu in waste samples. The system's efficiency curve was calculated by modelling gamma sources in the energy range of interest and validated by spectra measurements of 177Lu and 99mTc sources. Correction factors accounting for true coincidence summing (TCS) effect were simulated for 177Lu, 177mLu and 99mTc and they were applied to the spectrum measurement of a waste sample model with known activities of 177Lu and 177mLu. Thus, an operational approach for activities quantification was tested comparing the results with the nominal values. No significant differences were observed between simulated and measured efficiency values. TCS correction factors are significant only for 177mLu (1.6 at 112.95 keV and 204.11 keV). Eventually, the proposed framework to quantify 177Lu in a waste sample allowed to estimate the 177Lu and 177mLu component activities within a maximum 16% uncertainty. Results show that the HPGe model could be a powerful resource for a wide range of applications in daily clinical routine and it could be used to build a simple quality assurance program to monitor the detector response constancy in time.

A benchmark for Monte Carlo simulations in gamma-ray spectrometry Part II: True coincidence summing correction factors

The goal of this study is to provide a benchmark for the use of Monte Carlo simulation when applied to coincidence summing corrections. The examples are based on simple geometries: two types of germanium detectors and four kinds of sources, to mimic eight typical measurement conditions. The coincidence corrective factors are computed for four radionuclides. The exercise input files and calculation results with practical recommendations are made available for new users on a dedicated webpage.

True coincidence summing correction factor for point source geometry with PHITS

In this study, it has been shown that the true coincidence summing correction factor can be obtained for the first time using the PHITS Monte Carlo program. Determining this correction factor using different methods and tools in each laboratory to increase the possibility of achieving high-efficiency measurement conditions is still popular in gamma-ray spectrometry. By using 133Ba, 152Eu, 134Cs, and 60Co point sources, the true coincidence summing factor was investigated in both near and far counting geometries for 15 different energy values. GESPECOR software was used to validate the results obtained with PHITS. A remarkable agreement was obtained between PHITS and GESPECOR, with a discrepancy of less than 3%. With this study, a new tool has been proposed to obtain the true coincidence summing factor, which is one of the significant correction factors investigated/calculated in gamma-ray spectrometric studies.

True coincidence summing correction for a BEGe detector in close geometry measurements

The true coincidence summing correction factor for a Broad Energy Germanium detector has been calculated at far and close geometry set-up using radioactive γ-ray sources. The correction factors were calculated using both experimental and analytical methods. Geant4 simulation was done to calculate the full-energy peak and total efficiencies of the detector. Standard, as well as fabricated mono-energetic γ-ray sources, were used for the γ-ray efficiency measurements. The simulated efficiencies of mono-energetic γ-ray sources were matched to the experimental γ-ray efficiencies by optimizing the detector parameters. The same parameters were used to obtain the full-energy peak and total efficiencies for γ-rays of current interest. Analytical and experimental correction factors were found to agree well with each other. The coincidence summing effect is found to be significant for source-to-detector distances less than 5 cm.

True coincidence summing corrections in HPGe detectors

The true coincidence effect is studied in two High Purity Germanium (HPGe) detectors for a variety of isotopes, source geometries and source to detector configurations, via computational tools based on Monte–Carlo simulations. Τhe upgraded patch of MCNP code MCNP–CP and the 2018 version of PENELOPE, which take into account the decay scheme of each cascade emitter, are used to calculate the Full Energy Peak Efficiency (FEPE) for the corresponding gamma-ray energies. The true coincidence correction (TCC) factor is calculated as the ratio of the FEPE derived for each nuclide taking into consideration the true coincidence effect, to the FEPE estimated without considering the phenomenon. In all cases, a satisfactory agreement is observed between the TCC factors calculated using MCNP–CP and PENELOPE 2018. Moreover, the results of the calculations are compared against experimentally derived efficiency values. The correction factors obtained using the TrueCoinc software are applied on experimentally determined FEPE curves, based on measurements performed using reference sources, and consequently the corrected data are compared against the simulations for the "non-coincidence" case. The results of this work contribute to the validation of the computational tools and codes used to study the true coincidence effect and determine the corresponding correction factors, providing useful data for gamma–spectrometry studies of cascade emitters.

Peak Area Consistency Evaluation in Gamma Spectrometry

Quantification of radionuclide activities in gamma spectrometry can be a challenging task. It depends on efficiency calibration, peak area calculation, nuclide decay data and correction factors, such as attenuation correction or true coincidence summing corrections. These quantities can present significant challenges to an accurate analysis. It is therefore desirable to have a way of assessing the quality of the radionuclide quantification that can be applied to samples with unknown activities and radionuclide compositions. A verification of the self-consistency of the analysis is one possible way of accomplishing this. In gamma spectrometry it is possible to calculate radionuclide activities using information from multiple gamma emission energies. This leads to an overdetermined system for which the solution can be used to look for inconsistencies. By calculating the recovered peak areas from the radionuclide activities and comparing these to the measured peak areas, outliers can be identified and by resolving these inconsistencies the analysis of the spectrum can be improved. This peak area consistency evaluation can be used to find incorrect shape of the efficiency calibration, missing interferences in the nuclide decay data, and point to peaks where the peak area calculation needs to be optimized. The performance of the method has been shown on a simple spectrum consisting of three radionuclides that are interfering with each other as well as a complex spectrum with unknown radionuclide composition and activities. The method will be integrated into a future version the Genie 2000 Gamma Spectroscopy Software.

True Coincidence Summing Correction for Cylindrical Volume Samples in γ-ray Spectrometry

True Coincidence Summing Correction for Cylindrical Volume Samples in γ-ray Spectrometry

Coincidence summing corrections factors calculated for volume 152Eu sources in γ-ray spectromtery using Monte Carlo techniques

True coincidence summing (TCS) correction factors were determined for 152Eu volume sources used for γ-ray efficiency calibration as the ratio of full energy peak efficiency (e) simulated by MCNP5 code to the apparent full energy peak efficiency (eapp) determined experimentally. The results were compared to those calculated by TrueCoinc software and then validated using certified environmental radioactive samples. The dependance of 152Eu and 133Ba TCS factors on volume sample and matrix was investigated. Finally, as our n-type HPGe detector is very sensitive to low energy photons, the contribution of the γ–X coincidence summing to TCS factors for 152Eu and 133Ba sources in volume soil samples was studied.

Experimental validation of corrections factors for \u03b3\u2013\u03b3 and \u03b3\u2013X coincidence summing of 133Ba, 152Eu, and 125Sb in volume sources

True coincidence summing correction factors for 133Ba, 152Eu and 125Sb were determined experimentally for a small volume source and compared with correction factors obtained with three softwares (EFFTRAN-X, GESPECOR and VGSL). The radionuclides investigated have a relatively challenging decay scheme and their spectra are known to suffer from losses due to summation (γ–γ, γ–X and X–X) when measured at close distances on a HPGe detector sensitive to low energy photons. This study shows that the softwares were in good agreement with each other and the experimental data and the calculated activity was consistent with the activity in the volume source.

Efficiency calibration of an on-line detection device for fuel rod failure in a PWR

This paper describes a method of calibrating the efficiency of an on-line detection device for fuel rod failure in a pressurized water reactor. 214Am, 137Cs, 60Co and 24Na were selected to produce 4 sets of liquid calibration sources, and a calibration system that could simulate the on-site measurement of the on-line detection device was established. Efficiency calibration was performed against γ-ray lines, which could be identified by a LaBr3(Ce) detector. After a true coincidence summing correction, an efficiency curve of the on-line detection device for fuel rod failure was obtained, with a calibration uncertainty of 3.5%.

A method for the complete analysis of NORM building materials by γ-ray spectrometry using HPGe detectors

A methodology including software tools for analysing NORM building materials and residues by low-level gamma-ray spectrometry has been developed. It comprises deconvolution of gamma-ray spectra using the software GALEA with focus on the natural radionuclides and Monte Carlo simulations for efficiency and true coincidence summing corrections. The methodology has been tested on a range of building materials and validated against reference materials.

Efficiency calibration of a HPGe detector for the measurement of the primary coolant

This paper describes a method of calibrating the efficiency of a Ge γ-ray spectrometer. 226Ra and 232Th were selected to produce the soil calibration source, and then several γ-rays with high emission probabilities in 226Ra’s decay products and 232Th’s decay products, along with 2754 keV γ-rays of 24Na in the primary coolant sample of PWR, were employed to perform efficiency calibration. After self-absorption correction and true coincidence summing correction, we obtained the efficiency curve of a Φ70 × 30 mm aqueous calibration source over the high energy range (1120–2754 keV).

Calculation of Coincidence Summing Correction Factors for an HPGe detector using GEANT4

The aim of this paper was to calculate the True Coincidence Summing Correction Factors (TSCFs) for an HPGe coaxial detector in order to correct the summing effect as a result of the presence of 88Y and 60Co in a multigamma source used to obtain a calibration efficiency curve. Results were obtained for three volumetric sources using the Monte Carlo toolkit, GEANT4. The first part of this paper deals with modeling the detector in order to obtain a simulated full energy peak efficiency curve. A quantitative comparison between the measured and simulated values was made across the entire energy range under study. The True Summing Correction Factors were calculated for 88Y and 60Co using the full peak efficiencies obtained with GEANT4. This methodology was subsequently applied to 134Cs, and presented a complex decay scheme.

Validation of Monte Carlo model of HPGe detector for field-station measurement of airborne radioactivity

A Monte Carlo (MC) model of a mechanically-cooled High Purity Germanium detection system IDM-200-V™ manufactured by ORTEC® was created, optimized and validated within the scope of the Joint Research Project ENV57 ``Metrology for radiological early warning networks in Europe''. The validation was performed for a planar source homogeneously distributed on a filter placed on top of the detector end cap and for point sources positioned farther from the detector by comparing simulated full-energy peak (FEP) detection efficiencies with the ones measured with two or three different pieces of the IDM detector. True coincidence summing correction factors were applied to the measured FEP efficiencies. Relative differences of FEP efficiencies laid within 8% that is fully satisfactory for the intended use of the detectors as instruments for airborne radioactivity measurement in field-stations. The validated MC model of the IDM-200-V™ detector is now available for further MC calculations planned in the ENV57 project.

Equivalence of computer codes for calculation of coincidence summing correction factors – Part II

The aim of this study was to check for equivalence of computer codes that are capable of performing calculations of true coincidence summing (TCS) correction factors. All calculations were performed for a set of well-defined detector parameters, sample parameters and decay scheme data. The studied geometry was a point source of 133Ba positioned directly on the detector window of a low-energy (n-type) detector. Good agreement was established between the TCS correction factors computed by the different codes.

Experimental verification of mathematical efficiency modeling and true coincidence summing correction of the SAGe Well detector

The characterization and ray-tracing algorithm in ISOCS/LabSOCS has been extended to calculate full energy peak and total efficiencies for the Small Anode Germanium Well detector. The extension allows for true coincidence summing correction using the standard algorithm in the Genie 2000 software. The accuracy of the full energy peak efficiency calculation and the coincidence summing correction has been experimentally validated to be the same as for non-well detectors.

Building-up a code for the purpose of TRUE coincidence summing correction in gamma-ray spectrometry with EGS4

Abstract In the presented study, a code was created for the purpose of true coincidence summing (TCS) correction factors for 134 Cs. The created code was implemented in EGS4 Monte Carlo simulation package. TCS factors were determined for nine different energies for different detector–source geometries. The calculated results were successfully validated by an empirical method using a point 134 Cs radioactive source and a p-type HPGe detector having 55% relative efficiency. Although the code created gives TCS factors only for 134 Cs, the technique presented can be used to obtain the factors for any radionuclide used in gamma-ray spectrometry.

Characterisation of a radionuclide specific laboratory detector system for the metallurgical industry by Monte Carlo simulations

Abstract One of the outputs of the European Metrology Research Programme project “Ionising radiation metrology for the metallurgical industry” (MetroMetal) was a recommendation on a novel radionuclide specific detector system optimised for the measurement of radioactivity in metallurgical samples. The detection efficiency of the recommended system for the standards of cast steel, slag and fume dust developed within the project was characterized by Monte Carlo (MC) simulations performed using different MC codes. Capabilities of MC codes were also tested for simulation of true coincidence summing (TCS) effects for several radionuclides of interest in the metallurgical industry. The TCS correction factors reached up to 32% showing that the TCS effects are of high importance in close measurement geometries met in routine analyses of metallurgical samples.

A laboratory exercise on systematic effects in gamma ray spectrometry

A laboratory exercise for calculation of true coincidence summing correction factors as well as calculating the effect of deviations between sample and standard source (filling height) was developed. This laboratory exercise was held in a masters course in nuclear chemistry the first time during fall 2013. The aim of the exercise was to high-light the importance of correcting for biases due to different systematic effects in gamma spectrometric measurements.

True coincidence summing correction and mathematical efficiency modeling of a well detector

True coincidence summing (TCS) occurs when two or more photons are emitted from the same decay of a radioactive nuclide and are detected within the resolving time of the gamma ray detector. TCS changes the net peak areas of the affected full energy peaks in the spectrum and the nuclide activity is rendered inaccurate if no correction is performed. TCS is independent of the count rate, but it is strongly dependent on the peak and total efficiency, as well as the characteristics of a given nuclear decay. The TCS effects are very prominent for well detectors because of the high efficiencies, and make accounting for TCS a necessity. For CANBERRA׳s recently released Small Anode Germanium (SAGe) well detector, an extension to CANBERRA׳s mathematical efficiency calibration method (In Situ Object Calibration Software or ISOCS, and Laboratory SOurceless Calibration Software or LabSOCS) has been developed that allows for calculation of peak and total efficiencies for SAGe well detectors. The extension also makes it possible to calculate TCS corrections for well detectors using the standard algorithm provided with CANBERRAS׳s Spectroscopy software Genie 2000. The peak and total efficiencies from ISOCS/LabSOCS have been compared to MCNP with agreements within 3% for peak efficiencies and 10% for total efficiencies for energies above 30keV. A sample containing Ra-226 daughters has been measured within the well and analyzed with and without TCS correction and applying the correction factor shows significant improvement of the activity determination for the energy range 46–2447keV. The implementation of ISOCS/LabSOCS for well detectors offers a powerful tool for efficiency calibration for these detectors. The automated algorithm to correct for TCS effects in well detectors makes nuclide specific calibration unnecessary and offers flexibility in carrying out gamma spectral analysis.