Efficiency Calibration Curve Research Articles

Study of a method for theoretical calculation of the efficiency of a LaBr3(Ce) for detecting gamma-rays from point sources

A theoretical model for calculating the full-energy peak efficiency of scintillator detector is proposed in this paper. The effective penetration distance of gamma-rays in Ø3.81cm × 3.81 cm LaBr3(Ce) crystal, aluminum shell and MgO reflector is analyzed. The calculation model for point source detection efficiency is derived, and the attenuation of gamma-rays in the detector shell is computed by theoretical calculation method. This method is used to calculate the efficiency of LaBr3(Ce) with a size of Ø3.81 × 3.81 cm for detecting gamma-rays from point sources of 137Cs and 60Co located in different positions. Compared with experimental data and Monte Carlo (MC) simulation results, the maximum relative deviation is less than 5%. The attenuation of gamma-rays with an energy of 60 keV is more than 50%. The fitted efficiency calibration curve in the energy range of 60 keV–1500 keV is in good agreement with the simulation results. The results show that this method is suitable for calculating the efficiency of the LaBr3(Ce) detector using point sources, especially for analyzing low-energy gamma ray sources. By taking into account the attenuation of the gamma-rays by the detector shell, the measurement accuracy can be effectively improved. The proposed method can be extended for the efficiency calibration of scintillator detectors with various shapes and provides a new approach for 'source-less' efficiency calibration of detectors.

Validation of Tritium Calibration Curve in CIEMAT/NIST Activity Measurement Using Non Linear Least Squared Fittings and Calculations of the Half-Life and Decay Constant of Potassium-40

Non-linear curve fitting of tracer efficiency is one of the uncertainty contributors in CIEMAT/NIST method for specific activity measurement and half-life evaluation of radionuclide. This study applied least squared fitting of four different polynomials to validate the tracer efficiency calibration curve for the specific activity measurements of nine Potassium Chloride samples from which half-life and decay constants were computed. All samples were measured using TR1000 Liquid Scintillation Counter and the results of the relative standard uncertainties in tracer interpolated efficiencies associated with the least square fit analysis were found to be 8.363%, 8.076%, 7.941% and 8.767% for polynomials of n = 2, n = 3, n = 4 and n = 5, respectively. The corresponding values of 40 K specific activity, from the application of empirical efficiencies generated with these polynomials were found to be (16.541, 16.540, 16.537 and 16.548) Bq/g respectively. From these measured specific activity values, the computed half-life and decay constants were found to be (1.2518, 1.2519, 1.2521 and 1.2513) ×109 y (for n = 2, n = 3, n = 4, and n = 5), respectively, and (5.365, 5.5364, 5.5354 and 5.5391) ×10-10 y-1 respectively. All values were found to be in good agreement with results of other literatures. However to minimize uncertainty associated with empirically generated tracer interpolation efficiencies, least squared fit analysis of tracer calibration curve should be done, with control trials using different polynomials so as to obtain the best fit.

Quantitative radionuclide analysis protocol in a radiological and nuclear mobile laboratory / Protocolo de análise quantitativa de radionuclídeos em um laboratório radiológico e nuclear móvel

This study establishes a quantitative analysis protocol of radionuclides in a radiological and nuclear mobile laboratory of the Brazilian Army's Institute of Chemical, Biological, Radiological and Nuclear Defense. The gamma spectrometry technique was used, by a HPGe detector, to identify certified gamma-emitting radioactive sources (Am-241, Cs-137 and Co-60) present in a standard solution diluted in a Marinelli flask of 4L. Energy, resolution and efficiency calibration curves were determined using the LabFit software, for this detector, in the considered geometry. The results show to be satisfactory the linear adjustment (Channel versus Energy) of set points have been obtained experimentally which was confirmed by the determination coefficient achieved (). Besides that, it could be also verified that the exponential function was the mathematical model that best represented the answer of the HPGe detector energy resolution and that the mathematical adjustment options provided by LabFit which allowed to correlate the counting efficiency with the energy of each photopeak, despite the lack of a greater amount of energy. To define specific activities, the measurement errors between theoretical and experimental values were less than 4%, evidencing the reasonable responsiveness of the measurement system.

Determination of the coincidence summing factor by Monte Carlo method using MCNP–CP and PENNUC codes

In gamma spectrometry, the quantitative information about the composition of elements present in the experimental samples can be obtained from the efficiency calibration curve, the radioactivity, and the gamma emission intensity of the radioactive. The efficiency of the detector is often affected by the coincidence summing effect. The correction of the coincidence summing factors can be done through the software based on the efficiency transfer method or Monte Carlo simulation. In this study, two Monte Carlo simulation software, MCNP‒CP and PENNUC, were applied to calculate the coincidence summing factors of four radioactive 22Na, 60Co, 133Ba, and 134Cs by the simulation method. The calculated models from the benchmark with two types of detectors of n-type and p-type, using different source geometries such as point source, water, soil, and filter samples, were used. This study aimed to validate the spectral response as well as to compare the coincidence summing factors between MCNP‒CP and PENNUC. The results showed that the coincidence summing factors calculated by two simulation software gave a good agreement with an average relative deviation of less than 2%. The coincidence summing factors calculated by two simulation programs were verified by the statistical T-test with a linear correlation value of rxy = 0.995.

Radioactivity analysis for EPS waste using organic solvents

In this study, the recovery rates of the dissolution method for radioactivity analysis of expandable polystyrene (EPS) with a liquid scintillation counter (LSC) using tetrahydrofuran (THF), toluene, and acetone as solvents were estimated. The detection efficiency calibration curve for each solvent was derived. Two methods—the volumetric ratio method and the quenching agent method—were used to prepare quench source sets, and calibration curves were derived by linking the data from the two quench source sets. The R2 value of the calibration curve for THF was found to be 0.984. The relationship between the mass of dissolved EPS and the quench level was estimated: the quench level increased as the mass of dissolved EPS increased. Premix and postmix dissolution methods were tested. The recovery rates using THF with the premix method were 84.9 ± 0.9% and 96.5 ± 1.5% for 3H and 14C, respectively. Furthermore, the stability of the recovery rate over time when using THF was evaluated. The dissolution method with the premixed solution exhibited a more stable recovery rate over time. The dissolution methods were found to be applicable for analysis using LSC, and THF was found to be the most suitable solvent for the proposed method.

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.

Study of mathematical functions to fit detector efficiency curve in gamma ray energy range from 59.54 keV up to 1408.01 keV

Recently, there have been several significant improvements in the area of the radiation detection system and its instruments, especially those using scintillation or semiconductor gamma ray detectors. Scientists and technicians are interested in studying this progress, which can be useful for the detector's operation and its basic properties, such as energy, shape, and efficiency calibration. In this work, an extended study of various mathematical formulas was conducted to obtain the efficiency best-fitting function, that covers the measured values from low to high energy regions. They can be used to represent the efficiency of a high-purity germanium detector in the regions where accuracy and maximum speed in optimizing the calibration process are very important for gamma spectroscopy. Determination of the activity of environmental samples mainly depends on the efficiency calibration curve of the detection system. The gamma ray energy in the range from 59.54 up to 1408.01 keV used in this work was obtained by using a set of standard radioactive gamma ray sources of certified intensity. The current data analysis shows that most of the mathematical formulas, which represent the fitting curve for the detector full-energy peak efficiency, were quite agreeable with the experimental results.

Qualification of gamma spectrometry measurement for the radiological characterization of mixed VLLW cables in particle accelerators

In the framework of maintenance activities in particle accelerators, such as upgrades and dismantling, a large number of activated equipment are removed from the accelerator complex and require characterization in view of their disposal as radioactive waste. In particular, cables can be of different types. This feature induces variations of the efficiency calibration curves due to the variation of the material composition, source distribution and density. Hence, quantifying the activities of the gamma-emitting radionuclides can be quite challenging for mixed cables. In this article, we propose a new qualification methodology, based on gamma spectrometry, in order to assess the activity results uncertainties of gamma-emitting radionuclides. This new methodology is developed to define the envelop efficiency calibration curves and allows for the establishment of more accurate activity values with their corresponding uncertainties.

Developing a software for self-absorption correction for gamma spectrometry of soil and water samples based on MCNP5 Monte Carlo simulations

Gamma spectroscopy using HPGe is one of the most effective methods in determining the concentration of gamma emitting radionuclides in environmental samples. The purpose of this study is obtaining the efficiency calibration curves for the HPGe detector using MCNP5 Monte Carlo code, and designing appropriate software for correction of self-absorption caused by changes in density, height, and geometry of different samples. For this purpose the detector was simulated using MCNP5 Monte Carlo code, and the detector calibration curves were obtained for different geometries and heights, and appropriate software was designed for efficiency calibration. The results obtained in this study, show that changing the height, geometry, and density of the samples have significant effects on the detector efficiency because of the changes in self-absorption of the samples. Comparison of the self-absorption correction using the software, and the results of simulations show that designed software can predict the calibration curves for the new samples in different energies with error much less than 1%.

A new gamma spectroscopy methodology based on probabilistic uncertainty estimation and conservative approach

The gamma spectroscopy technique is commonly used in many applications to evaluate the activity of gamma emitters in a given sample. This assessment of activity is of particular interest for the disposal of radioactive waste or for clearance purposes. However, for these specific applications, one needs to show that the evaluated activities are reasonably conservative. This paper shows an application of a methodology developed to quantify the efficiency calibration curve uncertainties originating from a test case sample and its associated geometry modelling. Therefore, the effects of enclosing geometries on the activity measurement results are discussed. The purpose is to provide an example of uncertainty analysis for an approach that could be applied to other studies in which a conservative estimation of the activity is required.

Improving the efficiency in the detection of gamma activities in environmental soil samples: influence of the granulometry and soil density

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.

An alternative methodology to determine 210Pb activity soil profiles

Unsupported 210Pb (Pbexc) is generated in air and is subsequently deposited on soil surface. The Pbexc can be used for sediment dating, soil erosion/sedimentation and air mass studies.In many cases, 210Pb activity determination (gamma ray 46.5 keV) cannot be performed due to the lack of efficiency calibration curve, especially when radioactive patron source is not available.This work presents an alternative methodology to obtain the 210Pb activity values, based on the activity definition and the attenuation coefficient determinations and assuming that soil samples coming from depth higher than 25 cm only contain 210Pb generated in the soil (Pbexc free, i.e., for those soil layers the 210Pb activity is equal to the 226Ra activity, at secular equilibrium).The proposed methodology was evaluated using soils from La Plata region, Argentina. The same soil samples were also analyzed in a second laboratory by the conventional methodology. The obtained results indicated that the proposed procedure can be used as a good alternative in cases where a calibration sample is not available.

Effect of Partial Dependence of Photopeak Data on The Calculations of NaI(Tl) Detector Spectrum

Partial dependence of photopeak data of ɣ-ray energies is considering apart of peak channels after subtracting background (including Compton distribution) and obtaining symmetric Gaussian distribution, then considering this part to obtain other total data of peak. This was investigated by using NaI(Tl) detector with Eu-152, Ra-226 and Cs-137 point sources. For the isolated peaks of Eu-152, Gaussian shape is obtained, and the areas between ±σ and ±0.5σ were determined and efficiency is obtained. The calculated transformation to total data of peaks gave excellent agreement with the ordinary case. The overlap between the two peaks at 609.3 (Ra-226) and 661.6 keV (Cs-137) is studied with using σ values from data when sources are separated, and counts in peaks centroids. The data of each peak is "restored" and compared with that when sources are separated and gave a 98% agreement. Also the overlap between the two peaks at 1120 and 1238 keV (Ra-226) is studied with adopting the σ values from the shape calibration curve of Eu-152 and centroid counts in the same way as for the Ra-226 and Cs-137 case. The resultant peaks areas are compared with those obtained from efficiency calibration curve of Eu-152. However results here are of lower agreement.

Relative efficiency calibration for determining isotopic composition and age of HEU items by passive non-destructive gamma spectrometry

The observation of the 239 keV gamma line from 232U decay in high-enriched uranium (HEU) samples prompted us to utilize 232U (with main gamma energies of its daughters at 239, 583, 763, and 860 keV) as a mediator isotope for performing relative (intrinsic) efficiency calibration among 232U, 234U, 235U, 238U, and 214Bi isotopes. By this way, the isotopic composition and age of HEU samples can be derived from activity ratios constituted between pairs of these isotopes on the basis of a common relative efficiency calibration curve. The method proved to be a useful tool for γ-spectrometric characterization of HEU items, especially of weapon grade, shielded uranium material.

Analysis of Ores and its Purified Constituents by γ‐Spectrometry with Calculation of Uranium Isotopic Atom, Mass, and Activity Ratios

The physical verifications, that the national and international inspectors carry out in order to perform a credibility control, often consist in the measurement of physical quantities, related to the declared nuclear material properties, by Non‐destructive Assay (NDA). Analysis of ores and its purified constituent's samples has been carried out in this work using non‐destructive gamma assay technique. The spectrometer based on HpGe detector and its electronics was calibrated using standard IAEA multi‐lines gamma sources. The efficiency calibration curve was plotted for broad gamma energies; 50–2600 keV. The gamma transition of 235U (143.7, 163.3, 185.7, and 205.3 keV) and 238U (63, 766.3, and 1001.03 keV) were used for qualitative and quantitative assay of the samples. The specific activities of the samples were calculated based on the determined efficiency, branching ratio (emission probability per disintegration), mass of sample and count rate of the characteristics gamma transitions of uranium isotopes at fixed geometrical conditions. A simplified equation was derived for calculation of 235U atom ratios. The results of calculation show natural origin of the analyzed samples; around 0.72 %. Where, the anthropogenic 236U was not detected at all in the spectra. The uranium activity ratios (235U/238U) were calculated based on the measured activity. The uranium isotopic mass and total uranium content of the investigated samples were also calculated. The results obtained are depicted, tabulated and discussed in comparison with recent published national and international works.

Calibration of 4π NaI(Tl) detectors with coincidence summing correction using new numerical procedure and ANGLE4 software

The 4π NaI(Tl) γ-ray detectors are consisted of the well cavity with cylindrical cross section, and the enclosing geometry of measurements with large detection angle. This leads to exceptionally high efficiency level and a significant coincidence summing effect, much more than a single cylindrical or coaxial detector especially in very low activity measurements. In the present work, the detection effective solid angle in addition to both full-energy peak and total efficiencies of well-type detectors, were mainly calculated by the new numerical simulation method (NSM) and ANGLE4 software. To obtain the coincidence summing correction factors through the previously mentioned methods, the simulation of the coincident emission of photons was modeled mathematically, based on the analytical equations and complex integrations over the radioactive volumetric sources including the self-attenuation factor. The measured full-energy peak efficiencies and correction factors were done by using 152Eu, where an exact adjustment is required for the detector efficiency curve, because neglecting the coincidence summing effect can make the results inconsistent with the whole. These phenomena, in general due to the efficiency calibration process and the coincidence summing corrections, appear jointly. The full-energy peak and the total efficiencies from the two methods typically agree with discrepancy 10%. The discrepancy between the simulation, ANGLE4 and measured full-energy peak after corrections for the coincidence summing effect was on the average, while not exceeding 14%. Therefore, this technique can be easily applied in establishing the efficiency calibration curves of well-type detectors.

SU-F-T-368: Improved HPGe Detector Precise Efficiency Calibration with Monte Carlo Simulations and Radioactive Sources

Purpose: To obtain an improved precise gamma efficiency calibration curve of HPGe (High Purity Germanium) detector with a new comprehensive approach. Methods: Both of radioactive sources and Monte Carlo simulation (CYLTRAN) are used to determine HPGe gamma efficiency for energy range of 0–8 MeV. The HPGe is a GMX coaxial 280 cm3 N-type 70% gamma detector. Using Momentum Achromat Recoil Spectrometer (MARS) at the K500 superconducting cyclotron of Texas A&M University, the radioactive nucleus 24 Al was produced and separated. This nucleus has positron decays followed by gamma transitions up to 8 MeV from 24 Mg excited states which is used to do HPGe efficiency calibration. Results: With 24 Al gamma energy spectrum up to 8MeV, the efficiency for γ ray 7.07 MeV at 4.9 cm distance away from the radioactive source 24 Al was obtained at a value of 0.194(4)%, by carefully considering various factors such as positron annihilation, peak summing effect, beta detector efficiency and internal conversion effect. The Monte Carlo simulation (CYLTRAN) gave a value of 0.189%, which was in agreement with the experimental measurements. Applying to different energy points, then a precise efficiency calibration curve of HPGe detector up to 7.07 MeV at 4.9 cm distance away from the source 24 Al was obtained. Using the same data analysis procedure, the efficiency for the 7.07 MeV gamma ray at 15.1 cm from the source 24 Al was obtained at a value of 0.0387(6)%. MC simulation got a similar value of 0.0395%. This discrepancy led us to assign an uncertainty of 3% to the efficiency at 15.1 cm up to 7.07 MeV. The MC calculations also reproduced the intensity of observed single-and double-escape peaks, providing that the effects of positron annihilation-in-flight were incorporated. Conclusion: The precision improved gamma efficiency calibration curve provides more accurate radiation detection and dose calculation for cancer radiotherapy treatment.

Design and fabrication of an in situ gamma radioactivity measurement system for marine environment and its calibration with Monte Carlo method

Simulation, design and fabrication of a sealing enclosure is carried out for a NaI(Tl) 2″×2″ detector, to be used as in situ gamma radioactivity measurement system in marine environment. Effect of sealing enclosure on performance of the system in laboratory and marine environment (distinct tank with 10m3 volume) were studied using point sources. The marine volumetric efficiency for radiation with 1461keV energy (from 40K) is measured with KCl volumetric liquid source diluted in distinct tank. The experimental and simulated efficiency values agreed well. Marine volumetric efficiency calibration curve is calculated for 60keV to 1461keV energy with Monte Carlo method. This curve indicates that efficiency increasing rapidly up to 140.5keV but then drops exponentially.

Monte Carlo simulation of gamma-ray interactions in an over-square high-purity germanium detector for in-vivo measurements

The developments of high-purity germanium detectors match very well the requirements of the in-vivo human body measurements regarding the gamma energy ranges of the radionuclides intended to be measured, the shape of the extended radioactive sources, and the measurement geometries. The Whole Body Counter (WBC) from IFIN-HH is based on an “over-square” high-purity germanium detector (HPGe) to perform accurate measurements of the incorporated radionuclides emitting X and gamma rays in the energy range of 10 keV–1500 keV, under conditions of good shielding, suitable collimation, and calibration. As an alternative to the experimental efficiency calibration method consisting of using reference calibration sources with gamma energy lines that cover all the considered energy range, it is proposed to use the Monte Carlo method for the efficiency calibration of the WBC using the radiation transport code MCNP5. The HPGe detector was modelled and the gamma energy lines of [Formula: see text]Am, [Formula: see text]Co, [Formula: see text]Ba, [Formula: see text]Cs, [Formula: see text]Co, and [Formula: see text]Eu were simulated in order to obtain the virtual efficiency calibration curve of the WBC. The Monte Carlo method was validated by comparing the simulated results with the experimental measurements using point-like sources. For their optimum matching, the impact of the variation of the front dead layer thickness and of the detector photon absorbing layers materials on the HPGe detector efficiency was studied, and the detector’s model was refined. In order to perform the WBC efficiency calibration for realistic people monitoring, more numerical calculations were generated simulating extended sources of specific shape according to the standard man characteristics.

Mathematical method to calculate full-energy peak efficiency of detectors based on transfer technique

The full-energy peak efficiency of high-purity germanium well-type detector is extremely important to calculate the absolute activities of natural and artificial radionuclides for samples with low radioactivity. In this work, the efficiency transfer method in an integral form is proposed to calculate the full-energy peak efficiency and to correct the coincidence summing effect for a high-purity germanium well-type detector. This technique is based on the calculation of the ratio of the effective solid angles subtended by the well-type detector with cylindrical sources measured inside detector cavity and an axial point source measured out the detector cavity including the attenuation of the photon by the absorber system. This technique can be easily applied in establishing the efficiency calibration curves of well-type detectors. The calculated values of the efficiency are in good agreement with the experimental calibration data obtained with a mixed γ-ray standard source containing 60Co and 88Y.