Prompt Gamma-ray Neutron Activation Analysis Research Articles

Optimization design for moderator, reflector, and shielding of Deuterium-Deuterium neutron source

Deuterium-Deuterium (D-D) neutron source, which could be used in both laboratory and outdoors due to its light weight, small volume and low cost, has been widely applied in thermal neutron imaging (TNI) and prompt gamma-ray neutron activation analysis (PGNAA). And the its optimization design is to obtain highly intense thermal neutrons and low dose rate around the facility with light weight and compact volume. In this paper, the genetic algorithm (GA) combined with MCNP6 was applied to globally optimize moderator, reflector, and shielding structures. As a result, the optimized thermal neutron intensity increased by 1.68 times, while the dose rate, weight and volume respectively decreased by 37%, 52%, and 27%, compared with the data based on the current design. This method could be an effective tool for the compact neutron source design.

Determination of boron content in Tinkal ore samples with Geant4 using MCLLS method

A new Monte Carlo-Library Least Squares (MCLLS) method was developed for the neutron inelastic-scattering and thermal-capture analysis (NITA) techniques in real-time online analysis systems to determine boron content in Tinkal ore samples. The Geant4 toolkit was used to simulate the Prompt Gamma-ray Neutron Activation Analysis (PGNAA) system for the NITA technique. Tinkal ore samples were bombarded with 14 MeV neutron beams in order to represent neutrons released from the Deuterium-Tritium (DT) neutron generator. After the simulation of shooting Tinkal ore samples with 14 MeV neutron beams was completed, histograms were obtained from Geant4. Once the histograms are broadened according to the shape calibration of the BGO scintillation detector, the spectrum (broadened histograms) are ready to be used in the MCLLS process. A single element library was created by broadened histograms of the nine Tinkal ore samples. In addition, set #10 was selected to be an unknown sample and was used for validating MCLLS. After analysing the unknown sample spectrum, boron content was estimated by the single element library created by the MCLLS method. The estimated value of the boron content by MCLLS was consistent with the laboratory result.

Toward Developing Techniques─Agnostic Machine Learning Classification Models for Forensically Relevant Glass Fragments.

Glass fragments found in crime scenes may constitute important forensic evidence when properly analyzed, for example, to determine their origin. This analysis could be greatly helped by having a large and diverse database of glass fragments and by using it for constructing reliable machine learning (ML)-based glass classification models. Ideally, the samples that make up this database should be analyzed by a single accurate and standardized analytical technique. However, due to differences in equipment across laboratories, this is not feasible. With this in mind, in this work, we investigated if and how measurement performed at different laboratories on the same set of glass fragments could be combined in the context of ML. First, we demonstrated that elemental analysis methods such as particle-induced X-ray emission (PIXE), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), scanning electron microscopy with energy-dispersive X-ray spectrometry (SEM-EDS), particle-induced Gamma-ray emission (PIGE), instrumental neutron activation analysis (INAA), and prompt Gamma-ray neutron activation analysis (PGAA) could each produce lab-specific ML-based classification models. Next, we determined rules for the successful combinations of data from different laboratories and techniques and demonstrated that when followed, they give rise to improved models, and conversely, poor combinations will lead to poor-performing models. Thus, the combination of PIXE and LA-ICP-MS improves the performances by ∼10-15%, while combining PGAA with other techniques provides poorer performances in comparison with the lab-specific models. Finally, we demonstrated that the poor performances of the SEM-EDS technique, still in use by law enforcement agencies, could be greatly improved by replacing SEM-EDS measurements for Fe and Ca by PIXE measurements for these elements. These findings suggest a process whereby forensic laboratories using different elemental analysis techniques could upload their data into a unified database and get reliable classification based on lab-agnostic models. This in turn brings us closer to a more exhaustive extraction of information from glass fragment evidence and furthermore may form the basis for international-wide collaboration between law enforcement agencies.

Discrimination of phosgene from cyanogen chloride in recovered chemical munitions using tagged neutron interrogation with high-resolution gamma-ray spectroscopy

The associated particle (AP) technique has recently been used with a high-purity germanium γ-ray spectrometer to assess its capability to improve field identification of recovered chemical warfare (CW) materiel through prompt gamma-ray neutron activation analysis (PGNAA) measurements. A particularly challenging pair of CW agents commonly found in recovered munitions are phosgene (CG) and cyanogen chloride (CK), which have two of three elements in common, i.e. chlorine and carbon, but differ in the third being either oxygen or nitrogen. The detection of both latter elements is complicated by high oxygen concentration in the field environment which interferes with the small signal produced from the chemical agents. The matter is further complicated by the precautionary field practice of overpacking recovered munitions with vermiculite in larger steel multiple round containers (MRCs), which places additional oxygen-rich material in contact with the munition while further attenuating an already weak signal emitted from the munition center. This work reports quantitative results from realistic field measurements of CG and CK simulants in mock 4.2-inch (11 cm) mortar rounds overpacked with vermiculite in a large MRC. Results obtained with the AP technique are compared to those obtained with the traditional PGNAA approach for both overpacked- and bare-munition measurements. The AP technique is shown to provide a much more confident discrimination between the two chemicals, particularly for the more challenging field-relevant overpacked measurements, where a significant gain in sensitivity to all the key elements (chlorine, carbon, nitrogen and oxygen) is achieved.

Optimization study of chlorine detection sensitivity in concrete based on prompt gamma analysis using 252Cf neutron source

Chloride attack is a serious problem that decreases the durability of concrete structures of bridges and highways. A compact neutron salt meter with a252Cf neutron source and germanium (Ge) gamma-ray detector based on prompt gamma-ray neutron activation analysis (PGNAA) has been proposed to determine the chlorine concentration in concrete structures. The Optimization of the dimensions of its components, such as polyethylene (PE) moderator, graphite reflector, and lead shield, as well as the positions of the 252Cf source and the Ge detector has been performed to make it highly sensitive for the detection of gamma-rays of chlorine, in addition to lightweight and small volume for in situ use. The results demonstrated that gain factors of 2.5 and 2.2 were obtained for gamma-ray intensity of chlorine and chlorine-to-hydrogen ratio (CHR), respectively, whereas the weight and volume became 19.1% and 23.4%, respectively, compared with the reference setup. The effectiveness of optimization was confirmed by preliminary experiments.

Comparison between NIS and TNC channels for the detection of nickel in soil samples

The prompt gamma-ray neutron activation analysis (PGNAA) is a significant technique for determining the quantities of a variety of elements in natural materials, whether online or in situ, regardless of their chemical compounds. This study focused on evaluating the performance of a portable PGNAA setup based on a Genie 16 DD neutron generator to determine the minimum detectable concentration (MDC) of nickel in soil samples. Two separate reaction mechanisms were used to activate the samples. A CeBr3 detector was used to detect nickel gamma rays at 1331 and 1454 keV caused by neutron inelastic scattering, as well as those at 8553 and 8998 keV emitted following thermal neutron capture activations. The obtained MDC values for both reaction channels have improved as a result of the research.

Improving a PGNAA Technique to Detect Heavy Metals in Solid Samples

Prompt gamma-ray neutron activation analysis (PGNAA) is a useful approach for determining the concentrations of a variety of elements in natural materials, either online or in situ, without affecting their chemical forms in matter. The current research aimed to improve the yield of a portable PGNAA setup using a dc beam of 2.5 MeV neutrons and a CeBr3 detector to record gamma rays from neutron inelastic scatterings. It is impossible to avoid the superimposition of heavy metal gamma rays and those from the detector’s element. However, tests were carried out to improve the signal-to-background ratio. By assessing the minimum detectable concentrations (MDC) of chrome, titanium, and zinc in soil samples, the effectiveness of the new optimization was confirmed. The study shows an improvement in the MDC values.

Research on the optimization method for PGNAA system design based on Signal-to-Noise Ratio evaluation

In this research, for improving the measurement performance of Prompt Gamma-ray Neutron Activation Analysis (PGNAA) set-up, a new optimization method for set-up design was proposed and investigated. At first, the calculation method for Signal-to-Noise Ratio (SNR) was proposed. Since the SNR could be calculated and quantified accurately, the SNR was chosen as the evaluation parameter in the new optimization method. For discussing the feasibility of the SNR optimization method, two kinds of PGNAA set-ups were designed in the MCNP code, based on the SNR optimization method and the previous signal optimization method, respectively. Meanwhile, the single element spectra analysis method was proposed, and the analysis effect of single element spectra as well as element sensitivity were used for comparing the measurement performance. Since the simulation results showed the better measurement performance of set-up designed by SNR optimization method, the experimental set-ups were built for the further testing, finally demonstrating the feasibility of the SNR optimization method for PGNAA set-up design.

Measurement of talc in flour by the prompt-gamma ray neutron activation analysis method

Prompt gamma-ray neutron activation analysis method (PGNAA) was used to measure the talc content in flour. Neutron activation prompt gamma spectrum measured by NaI(Tl) detector has complex components, poor energy resolution, and high Compton plateau, how to obtain accurate element content from the prompt γ spectrum is one of the core problems of PGNAA. To reduce the systematic uncertainty caused by the variation of the neutron energy spectrum and γ self-absorption in different samples, the spectral decomposition method based on library least-squares was improved. As a result, the average relative deviation between the calculated values from measured spectra and the theoretical values based on the known composition was reduced from 6.1% to 0.3%. The relative uncertainty of 30 measurements on the same sample was reduced from 4.8% to 3.0%. The detection time can be reduced to 1min, which meets the requirement of on-line measurement for talc in flour.

Feasibility study of fast neutron-induced gamma ray imaging of large sample based on D-T neutron generator

Elemental imaging plays an important role in characterizing the chemical and physical properties of large samples. In this work, a position-sensitive technique using prompt gamma ray neutron activation analysis (PGNAA) was applied to image the internal composition of large samples with 10–20 cm thicknesses. An inelastic neutron scattering system consisting of a D-T neutron generator and a high-purity germanium (HPGe) detector was built and used for elemental distribution analysis of a large metal sample containing iron, titanium, and copper. The 2D elemental imaging of the three elements was performed using the designed system. The effect of inhomogeneous neutron field was also corrected using Monte Carlo simulations. The results indicate that ~4 cm spatial resolution can be achieved. The position-sensitive elemental analysis based on inelastic neutron scattering reaction is efficient for bulk metal sample analysis.

Dose rate evaluation in a laboratory for prompt gamma neutron activation analysis by Monte Carlo simulation

As an excellent tool, neutron generators have been used widely in prompt gamma-ray neutron activation analysis (PGNAA) technology. In this work, a new PGNAA laboratory was proposed to equip a D–T neutron generator. For safety reasons, radiation shielding of the laboratory was designed, and its protection efficiency was validated by using MCNP simulations and experiments. The results show that the proposed shielding can meet the radiation protection set by the International Commission on Radiological Protection and the Chinese government.

In situ experimental measurement of mercury by combining PGNAA and characteristic X-ray fluorescence

In our previous research, a new detection method was proposed to measure Hg and Pb simultaneously by combining Prompt Gamma-ray Neutron Activation Analysis (PGNAA) and X-ray Fluorescence (XRF) and proved by the Monte Carlo N-Particle (MCNP) simulation code. For further experimental verification, a combined measurement experimental facility, comprising an 241Am–Be neutron source, SAINT-GOBAIN Bismuth Germanate (BGO) as the γ-ray detector, and an NaI detector with 25 μm Be window as the X-ray detector, was presented. Specifically, the characteristic X-ray fluorescence of the Hg directly induced in this experimental facility was utilized to improve the limits of detection (LOD) of Hg instead of traditional excitation sources. The simulation and experiment results indicated that LOD for Hg by the combined measurement instrument was 19.4 mg kg−1. The empirical formula of the calibration curve in this method was given based on the aforementioned calculations.

Application of PGNAA utilizing thermal neutron beam for quantification of boron concentrations in ceramic and refractory neutron absorbers

A Prompt Gamma-ray Neutron Activation Analysis (PGNAA) facility was set up using a thermal neutron beam at Dhruva research reactor. It was utilized for non-destructive quantification of total boron in refractory neutron absorbers and 10B atom% in B4C ceramics having natural and enriched 10B composition by measuring the 478 keV prompt gamma-ray from 10B(n,αγ)*7Li. Self-shielding correction was carried out for higher boron concentration samples using chlorine as an internal standard. As a part of quality assurance, the results of PGNAA were compared with those obtained by in situ current normalized Particle Induced Gamma-ray Emission (PIGE) method.

MCNP benchmark of a 252Cf source-based PGNAA system for bulk sample analysis

A MCNP model of a252Cf source-based prompt gamma-ray neutron activation analysis (PGNAA) system for bulk sample analysis was benchmarked. The indium foils activation and aqueous samples containing chlorine were measured using the PGNAA system, and the experimental data compared to the simulations. The discrepancies between the measurements and simulations are within 6% and 20% for thermal neutron flux and prompt gamma-ray response, respectively. The results show that the simulations agree well with the measurements, and demonstrate the proposed MCNP model can represent the system.

The comparison of five neutron sources via 7Li(p,n) reaction for the design of a facility based on prompt gamma ray neutron activation analysis (PGNAA) in vivo detections of boron

Prompt Gamma Ray Neutron Activation Analysis (PGNAA) is a useful nondestructive method with numerous applications. In this study neutron yield from 7Li(p,n) reaction with proton energies of 2.5, 3, 4, 4.5 and 5 MeV was used in order to provide the necessary thermal beam to the investigated sample. The facility was designed and simulated using the MCNPX Monte Carlo code. The primary goal was the enhancement of the signal to noise ratio and the improvement of the detection limit of the system. An extensive series of simulations were performed for each source in order to examine the consequence of the solid angle which formed between the neutron beam and the collimator detector. Boron was used as an element which emits the prompt gamma rays and according to the simulations, 2.5 and 3 MeV protons beams offer the best performance, while for proton beam with energy in the range between 4-5 MeV the results indicate slightly poorer performance. Simulations are presented for the in-vivo PGNAA in the human liver.

Design of a PGNAA facility using D-T neutron generator for bulk samples analysis

A prompt gamma-ray neutron activation analysis (PGNAA) facility has been developed for the determination of elements in bulk samples. The basic design of the PGNAA facility is composed of three major components: A deuterium-tritium neutron generator, the neutron moderator and reflector, and a high-purity germanium detector. The Monte Carlo code was used to select materials of moderator and optimize geometrical size of the facility. Then the PGNAA facility was built based on the simulation results. The bulk aqueous samples containing chlorine and cadmium were analyzed with the facility. The neutron self-shielding effect of the bulk aqueous samples was also corrected. The results showed the minimum detectable concentration (MDC) of chlorine and cadmium were 2.58 ± 0.78 g/L and 0.05 ± 0.01 g/L, respectively. For mixture sample analysis, the relative deviations of calculated value and actual value for chlorine and cadmium were 5.1% and 2.0%, respectively.

Improving the sensitivity of fast neutron inelastic scatter analysis to iron using associated particle collimation

The purpose of this study is twofold; first, a prompt gamma-ray neutron activation analysis (PGNAA) system will be constructed and employed in order to find the approximate sensitivity to elemental iron upon spectroscopic analysis. Concurrently, a Monte Carlo (MC) simulation model of the same PGNAA system will be defined such that the neutron source and resulting gamma-ray emissions are temporally collimated using the neutron associated particle (AP) technique. The experimental and simulated gamma-ray spectra may then be compared – taking into account the technological parameters and physical limitations of the PGNAA system – to determine how the sensitivity of the system may be improved due to photon signal discrimination inherent to the application of AP timing.

Feasibility study on neutron energy spectrum measurement utilizing prompt gamma-rays

Abstract A new approach based on Prompt Gamma-ray Neutron Activation Analysis (PGNAA) was proposed for measuring neutron energy spectra . A system, which consisted of a high purity germanium (HPGe) detector and a multi-layer sample, was used to validate the method. The composite layers of the sample comprised of lead, polymethyl methacrylate, sodium chloride powder and borated polyethylene . Prompt gamma-rays emitted from Pb, H, O, C, Cl and B were selected to determine the incident neutron energy spectrum. The response function for the production of gamma rays from these elements by monoenergetic neutrons was obtained through Monte Carlo simulations. Then the neutron fields of Cf-252 neutron source and D-T neutron generator were investigated with this approach. With the measured prompt gamma-rays and the response matrix, the neutron spectra were obtained through the PSO algorithm. The unfolded results have a good agreement with the simulation spectrum.

Application of the Monte Carlo Library Least-Squares (MCLLS) approach for chromium quantitative analysis in aqueous solution

In the present work, a new in-situ prompt gamma-ray neutron activation analysis (PGNAA) setup was developed for the quantitative measurement of chromium (Cr) in aqueous solutions which consists of a 4" × 4″ inch Bismuth Germanate detector and a 300 mCi 241Americium-beryllium neutron source. A series of standard samples were prepared by dissolving Cr compounds in deionized water of analytical pure grade and measured using the in situ PGNAA setup. Quantitative spectrum analysis was conducted using Monte Carlo Library Least-Squares approach (MCLLS). Simulates of elemental library spectra were in silico modeled using the CEARCPG code, which was developed by Prof. Robin Gardner research group in North Carolina State University. The fitted spectra presented were in excellent agreement with the total experimental spectrum, and the correlation coefficients were all nearly 1. After applying the MCLLS approach, the minimum detectable concentration of Cr was 301.5 mg/L, better than that obtained with other setups, and the relative deviation of the Cr quantitative analysis accuracy was less than 4.09%.

Efficiency calibration of HPGe detector in a PGNAA system for the measurement of aqueous samples

In this work, a method was proposed for efficiency calibration of HPGe detector employed in a prompt gamma-ray neutron activation analysis (PGNAA) system for large aqueous sample analysis. Experimental measurements of a reference surface gamma-ray source were combined with efficiency transfer method to obtain efficiency of a volumetric source. Then efficiency curve over the energy range 0.5–8.5 MeV were determined with prompt gamma-rays of chlorine. To evaluate the performance of the calibration curve, an internal standard method was used to determine the aqueous sample containing manganese based on the calibration curve. The 7.058 MeV and 7.243 MeV manganese gamma-ray peaks were used to calculate the mass of manganese. The relative deviations of calculated values and actual value were 5.0% and 6.5%, respectively.