Nuclear Forensic Analysis Research Articles

Introduction to Nuclear Forensics Analysis Techniques

Abstract Nuclear forensics is the interdisciplinary branch of forensic science that deals with the analysis and examination of nuclear or other radioactive materials, or of evidence that is contaminated with radionuclides in the context of legal proceedings under international or national law related to nuclear security. To control and avoid the threat of terrorism posed by illicit trafficking and mismanagement, nuclear and other radioactive materials must be strictly regulated. Thus, the goal of nuclear forensic analysis is to discover what radioactive materials were confiscated, how, when, and where they were manufactured, and what their intended applications were. Nuclear forensic scientist has a wide array of analytical tools to use for detecting signatures in radioactive materials. These individual techniques can be sorted into three broad categories: bulk analysis tools, imaging tools, and microanalysis tools. Particular interest in nuclear forensics is particle morphology, isotopic composition of a material, presence of impurities, and microstructure. These properties can vary between materials of different origins due to varying processing or geological conditions, thus, allowing for discrimination of material history and prediction of provenance. This review article presents many key analytical techniques and discusses the main application and challenges of the most common techniques currently used in nuclear forensics analysis.

Advancing source reactor-type discrimination using machine learning techniques and SFCOMPO-2.0 experimental database

In recent years, nuclear forensic analysis has become crucial due to the growing global threat of nuclear terrorism and smuggling. Since 2005, extensive research has been conducted on identifying the origin of spent nuclear fuel, focusing on the source reactor-type discrimination, 235U enrichment of the fresh fuel, and the fuel exposure in the reactor (known as burnup). However, the majority of research relies on computed databases, which may lead to tracing discrepancies compared with actual situations. The present study employs the isotopic measurements from the experimental SFCOMPO-2.0 database to predict nuclear reactor types using Factor Analysis (FA) and various machine learning classification algorithms. The results reveal that FA is an effective method for dimension reduction and visualization. The FA-KNN, Random Forest (RF), and Multilayer Perceptron (MLP) algorithms are applied using a consistent dataset partition to ensure unbiased comparisons. The prediction results based on 10-fold stratified cross-validation are quite promising and the Receiver Operating Characteristic (ROC) curves for multi-class classification confirm the excellent generalization ability of models. Therefore, the application of machine learning techniques is highly effective for reactor-type forensics analysis, especially for RF and MLP.

Characterisation of sealed radioactive source for nuclear forensic purposes

Characterisation of sealed radioactive source for nuclear forensic purposes

Application of deep metric learning model to microscope image analysis for the determination of UOC samples in nuclear forensics analysis

Application of deep metric learning model to microscope image analysis for the determination of UOC samples in nuclear forensics analysis

Precise and accurate isotopic analysis of uranium and thorium in uranium ore concentrates using ICP-MS and their age dating for nuclear forensic analysis

Precise and accurate analysis of 235U/238U, 234U/238U, 230Th/234U and 230Th/232Th in 15 uranium ore concentrates (UOCs) was achieved using ICP-MS for nuclear forensic applications. A novel method was developed to dating UOCs.

In situ synthesis of PuCl3 and corresponding Raman and density functional theory vibrational modes

AbstractThe experimental and calculated Raman spectrum of PuCl3 has been reported for the first time. PuCl3 is a primary species found in plutonium metal refinement, specifically in pyrochemical salt processes including multicycle direct oxide reduction, metal chlorination, and electrorefining. As such, Raman signatures of PuCl3 could serve as potential forensic indicators of material process history. A novel technique for synthesizing PuCl3 from the in situ chlorination of plutonium metal with HCl was developed to establish these signatures. Cerium metal surrogates were utilized to ensure optimization of the plutonium experiments and to minimize personnel exposure, and all experiments were carried out in a Raman reaction chamber designed for air‐tight, high vacuum environments. In situ Raman spectroscopy was employed in conjunction with density functional theory (DFT) to investigate the vibrational modes of PuCl3. Associated mixed oxy and hydroxyl phases are also reported. The combined Raman and DFT results have eliminated inconsistencies in Raman mode assignments for the MX3 family of metal chlorides having P63/m symmetry, and IR modes derived from the DFT calculations are additionally presented. The data observed in this study are of potential interest to nuclear forensic analyses, nuclear sample aging, nuclear energy, plutonium processing, and stockpile stewardship.

Exploring band-free Raman microspectrometry combined with PCA and MCR-ALS for size-resolved forensic analysis of uranium in aerosols in a model nuclear atmosphere

Achieving non-destructive micrometer-scale molecular and structural analysis of uranic materials in atmospheric aerosols with traditional methodologies is a challenge. Spatially resolved analysis of uranium in actinide-bearing aerosols is critical for nuclear forensics. Although laser Raman microspectrometry enables this, for the normally low uranium concentrations in the aerosols the spectra are indiscernible (band-free) against pronounced background: trace analysis requires a push in analytical strategy. We combined laser Raman microspectrometry (utilizing two lasers (λ = 532 nm, λ = 785 nm)) with principal component analysis (PCA) and multivariate curve resolution–alternate least squares (MCR-ALS) to perform size-resolved analysis of uranium in aerosols. Uranium-specific Raman scatter bands corresponding to uranyl nitrate (860 cm−1), uranium sulphate (868 cm−1), uranyl chloride (816 cm−1) and uranium trioxide (839 cm−1) were detected. The 816 cm−1, 854 cm−1, 868 cm−1 bands were resolved by MCR-ALS and used to identify and map uranium in PM4.5 size aerosols. Based on spectral feature selection of the signature bands, PCA identified two sources of aerosol particles in model nuclear atmosphere - Sea spray for PM4.5 and re-suspension of ‘nuclear’ dust from a rare earth element (REE) mine for PM2.5. The MCR-ALS-resolved uranium bands showed the potential for attributive nuclear forensic analysis.

Trace Actinide Signatures of a Bulk Neptunium Sample.

In nuclear forensic analyses, measurements of actinide elements in a sample can assist with identifying interdicted or unknown materials. While these radiochemical signatures have been extensively investigated in uranium materials, less is known about bulk neptunium samples. This paper describes the measurement of trace actinide concentrations and isotopic profiles in a 237Np oxide sample. Uranium, plutonium, americium, and curium concentrations and isotopic profiles in the sample were determined and deemed potentially useful for distinguishing different sources of 237Np. Several different potential radiochronometry systems were also investigated; discordant results indicate that the Np sample was never completely purified of other actinide elements, or that subsequent contamination of the sample occurred. Few prior studies of neptunium materials have been reported, and these data suggest that trace actinide constituents could provide unique signatures to identify material out of regulatory control.

Chemical separation and measurement of platinum activation products

A method has been developed to purify and measure platinum radioisotopes in the presence of fission products and environmental constituents. The method uses a combination of cation exchange and anion exchange chromatography and selective precipitation steps to remove other radioisotopes from the sample. The addition of stable platinum carrier allows for a gravimetric determination of the chemical yield of the procedure. Overall, the method is fast, simple, and potentially applicable for rapid turnaround of unknown samples. Using this method, multiple platinum radioisotopes were measured in two different irradiation experiments. The measured ratios of the platinum radioisotopes clearly reflect the neutron spectrum of the irradiation, suggesting that platinum radioisotopes could be valuable signatures in nuclear forensic analyses.

In View of “On-Site” Nuclear Forensics and Assay of Fissile Materials in Sealed Packages by High-Resolution γ-Ray Spectrometry

Several incidences of nuclear smuggling during the past few decades have raised the demand for the development of a strong "on-site" nuclear forensic infrastructure. High-resolution γ-ray spectrometry (HRGRS) plays an important role in nuclear forensics. However, the existing methodologies, developed primarily for nuclear fuel cycle applications, are relative and rely on the availability of a standard, limiting their use for the absolute assay of special nuclear materials in nonstandard geometry samples with an unknown matrix, which is vital to make a quick "on-site" decision on the severity, potential radiological threat, and intended use of an interdicted package. In this work, a methodology has been developed using HRGRS for quantifying fissile (235U, 239Pu) and other radioisotopes, which is applicable to sealed packages without requiring the knowledge of the sample geometry and the matrices. By combining experiments and Monte Carlo simulations, an iterative methodology has been proposed for "point" to "extended" source absolute efficiency transformation and demonstrated further for the absolute isotopic assay of uranium and plutonium standards, mock-up nuclear forensic samples, and an unknown nuclear material mixture with a nonstandard geometry, compound matrices, and a wide variation in the elemental and isotopic compositions with a view to imitate an "on-site" experience. The present methodology requires an assay time of only a few minutes to an hour and thus promises "on-site" nuclear forensic analysis of suspected flagged packages at borders and ports using high-resolution γ-ray spectrometry. Furthermore, the present methodology is versatile and can also be adopted for wider applications, beyond nuclear forensics.

Prompt digestion and HPIC separation of rare earth elements in surrogate post-detonation debris material with detection by ICP-MS and gamma spectroscopy

Prompt analysis of fission products and rare earth elements (REE)s in post-detonation nuclear debris is critical for nuclear forensic analysis. In this work the compatibility of ammonium biflouoride fusion and microwave digestion in combination with high pressure ion chromatography (HPIC) separation was examined for the analysis of REEs. The refractory geological materials USGS G-2, QLO-1a, AGV-2 and BHVO-2 were used as surrogate post-detonation debris. The HPIC separation used a mixed bed ion exchange column with a gradient elution consisting of oxalic acid and diglycolic acid mobile phases. Quantitative recovery for seven REEs was achieved using the in-line HPIC-ICP-MS. An off-line HPIC method was also developed to separate U, Pu, and REE fission products. Collected fractions were analyzed by ICP-MS or gamma ray spectroscopy. The offline HPIC separation with detection of short-lived fission products with gamma ray spectroscopy had detection limits 5–20,000 times lower than quadrupole ICP-MS for stable REEs.

Separation of Americium from Curium through Oxidation State Control with Record Efficiency.

Separation of americium (Am) from curium (Cm) could greatly facilitate the development of advanced nuclear fuel cycles, help with accurate nuclear forensic analysis, and allow for more efficient recovery and utilization of the two strategic elements. In this work, an Am/Cm separation strategy based on the stabilization of pentavalent Am in a biphasic solvent extraction system using bismuthate as the oxidant and N,N,N',N'-tetraoctyl diglycolamide (TODGA) as the extractant was developed. The distinctive differences between Am(V) and Cm(III) in terms of both steric configuration and charge density afford record high Cm/Am separation factors (>104) through only one single contact in solvent extraction. This separation strategy possesses superior features including fast kinetics, long-time stability, no secondary solid radioactive waste generation, and applicability over a wide range of HNO3 acidities, making it promising for Am/Cm separation and analysis in a variety of applications.

Exercise Celestial Skónis: Part 2 – Emerging technologies and State of Practice of nuclear forensic analyses demonstrated during the 6th collaborative materials exercise of the nuclear forensics International Technical Working Group

The Nuclear Forensics International Technical Working Group conducted its sixth and largest Collaborative Materials Exercise, Celestial Skónis, in which laboratories from 20 countries (one virtual participant) and the European Commission, working with 15 law enforcement agencies, analyzed a set of samples containing special nuclear material as part of an elaborate mock nuclear forensics investigation. The nuclear materials used during the exercise included (1) depleted uranium and (2) stable cerium metal ingots contaminated on their surfaces with trace amounts of depleted uranium- and weapons grade plutonium-oxy-fluoride powders. This exercise also included traditional evidence (e.g., cut surfaces of pipes, toolmarks on plastic bags, and patent and latent fingerprints) comingled/contaminated with radioactivity. Participating laboratories processed traditional forensic evidence contaminated with radioactivity and analyzed nuclear materials in support of the mock investigation over a two-month period. These results were used to evaluate the “State of Practice” and identify promising “Emerging Technologies” in nuclear forensic science. This work is presented in two parts. Part 1 summarizes the history and purpose of these exercises, describes the design of the 6th and latest in this series, presents results of traditional forensic examinations on evidence contaminated with radioactivity, and summarizes the traditional and nuclear forensic evidence used to answer investigatory questions posed during the exercise. Part 2 summarizes results of nuclear forensic analyses that were conducted on the nuclear materials, giving special focus to the challenges of interpreting U and Pu isotopic results and the utility of those results for connecting people, places, things and events.

Exercise Celestial Skónis: Part 1 – History, purpose, design and results of traditional forensic examinations of the 6th Collaborative materials exercise of the nuclear forensics International Technical Working Group

The Nuclear Forensics International Technical Working Group conducted its sixth and largest Collaborative Materials Exercise, Celestial Skónis, in which laboratories from 20 countries (one virtual participant) and the European Commission, working with 15 law enforcement agencies, analyzed a set of samples containing special nuclear material as part of an elaborate mock nuclear forensics investigation. The nuclear materials used during the exercise included (1) depleted uranium and (2) stable cerium metal ingots contaminated on their surfaces with trace amounts of depleted uranium- and weapons grade plutonium-oxy-fluoride powders. This exercise also included traditional evidence (e.g., cut surfaces of pipes, toolmarks on plastic bags, and patent and latent fingerprints) comingled/contaminated with radioactivity. Participating laboratories processed traditional forensic evidence contaminated with radioactivity and analyzed nuclear materials in support of the mock investigation over a two-month period. These results were used to evaluate the “State of Practice” and identify promising “Emerging Technologies” in nuclear forensic science. This work is presented in two parts. Part 1 summarizes the history and purpose of these exercises, describes the design of the 6th and latest in this series, presents results of traditional forensic examinations on evidence contaminated with radioactivity, and summarizes the traditional and nuclear forensic evidence used to answer investigatory questions posed during the exercise. Part 2 summarizes results of nuclear forensic analyses that were conducted on the nuclear materials, giving special focus to the challenges of interpreting U and Pu isotopic results and the utility of those results for connecting people, places, things and events.

Application of radio-analytical technique for determination of “Age” of nuclear materials for nuclear forensics

Determination of “Age” – the time elapsed since the last chemical purification – of a nuclear material is an important parameter in Nuclear Forensic analysis. Estimation of age may give crucial acumen of the possible production facility and the declared origin – if available – in case of a suspected nuclear material which is out of regulatory control. Mass spectrometry is the most common analytical technique used for chronological studies due to its superior precision (lower uncertainty). Though alpha spectrometry can be used for age determination, it better suits for irradiated fuel based radio-chronology because of higher specific activity of irradiated actinides (actinides formed by irradiation of actinides within a reactor) like plutonium. This paper describes the application of alpha spectrometry for the age determination in some natural U-metal samples with known history. The method utilises the radioactive non-equilibrium existing between 234U and 230Th isotopes in the sample for the elucidation of age of the material. Optimisation of a chemical procedure for the separation of ultra-trace amount of thorium isotopes from bulk uranium material using double column anion exchange chromatography is also presented. The chemical recoveries of uranium and thorium obtained with the present method were >95%. The uncertainty in age determination was <10% and ∼15% for older (∼51 years) and newer (∼11 years) samples respectively. The method is also used to elucidate the age of an unknown uranium material and found to be 39 ± 4 years old.

The Role of Nuclear Forensics for Determining the Origin of Nuclear Materials Out of Regulatory Control and Nuclear Security

The international community recognizes the rise in theft and illicit trafficking of nuclear materials and radioactive sources—for malicious use and nuclear terrorism—as a serious threat. That is why a well-developed nuclear forensics capability is an integral part of a robust nuclear security program and a key element of nuclear security infrastructure. Both pre- and post-detonation nuclear forensics are vital for controlling theft and illicit trafficking of nuclear materials, as well as identifying and tracing their sources. Nuclear forensics analysis and interpretation processes for nuclear security is a systematic process that includes: (1) sample collection and categorization techniques and (2) detailed nuclear forensics analytical plans, which are a laboratory analysis of physical and chemical properties of the collected or seized nuclear and radioactive materials. Besides nuclear materials, the non-nuclear and biological materials present in seized nuclear materials can also provide important information about the source and origin of nuclear materials. Upon complete analysis of the seized materials, the data interpretation to trace the origin of the nuclear and radiological materials is one of the most critical steps to identifying the origin of the materials, which depends on the availability of similar data to compare. So, each country should have its own incident register system (IRS) and collaborate with the International Technical Working Group (ITWG), Incident and Trafficking Database (ITDB), and IAEA for data sharing and interpretation.

Impact of Precipitation Parameters on the Specific Surface Area of PuO2.

Controlling the properties of PuO2 through processing is of vital importance to environmental transport and fate, production of nuclear fuels, nuclear forensic analyses, stockpile stewardship, and storage of nuclear wastes applications. A number of processing conditions have been identified to control final product properties, including specific surface area (SSA), residual carbon content, adsorption of volatile species, morphology, and particle size. In this paper, a novel approach is developed for the prediction of PuO2 SSA via the synthetic route of Pu(IV) oxalate precipitation followed by calcination. The proposed model utilizes multivariate regression methodology and leave one out formalism to link Savannah River Site (SRS) precipitation and calcination production data to the SSA of the final product. A comparison among the models provides insight into the accuracy and ability to identify variations amongst the processing data. Additionally, the models may also be used to fit new data outside of the parameters explored in a production facility. Finally, the trained model was compared to a similarly trained conventional model form to illustrate the influence of precipitation parameters on the prediction of the final SSA. The models presented here attempt to provide new methods for more accurate prediction of the PuO2 product properties in a production scale environment for key environmental and nuclear applications.

Nuclear forensic analysis with laser ablation inductively coupled plasma mass spectrometry in CMX-6

The 6th Collaborative Materials Exercise, CMX-6, was organized by the Nuclear Forensic International Technical Working Group in 2018 and 2019. Two exercise samples, which had classical and nuclear forensic components, were distributed to nuclear forensic (NF) laboratories throughout the world. The goal of the exercise was to enable the NF laboratories to practice their capabilities under a realistic scenario, and share their experience in an open forum. Here we present the use of laser ablation triple quadrupole inductively coupled plasma mass spectrometry for the nuclear forensic examination of uranium and plutonium contaminated materials in CMX-6. Similarity or dissimilarity of exercise samples was established though trace element analysis and uranium and plutonium isotope ratio measurements.

Uranium Oxide Synthetic Pathway Discernment through Unsupervised Morphological Analysis

We present a novel unsupervised machine learning method for quantitative representation of scanning electron micrographs and its applications and performance for nuclear forensic analysis of uranium ore concentrates. The method uses a vector quantizing variational autoencoder followed by a histogram operation to encode a micrograph into a single dimensional representation, called the feature vector. The method requires no extant labeling of the data and can be applied over large datasets of micrographs with minimal human interaction. The representations generated are broadly descriptive of each micrograph and the microstructure of the material imaged. In the case of uranium ore concentrate analysis, the representations were amenable to processing reagent and ore concentrate species classification with accuracy of 81.8 % , which is competitive with state-of-the-art supervised networks [1]. The representations were also able to classify previously processing routes not included in the training set, were able to classify imaging parameters such as magnification (to 76.0 % accuracy), were able to classify fine grained process parameters such as calcining temperature (to 74.4 % accuracy), and their informatic properties indicate that they are generally descriptive of the image represented. This method can be applied across microstructure analysis fields to perform quantitative analysis without the need for labor intensive and possibly biased human analysis.

Laboratory facilities for nuclear forensic investigation in Malaysian Nuclear Agency

Nuclear forensic is a new field and a key element in nuclear security in any country. The purpose of nuclear forensic investigation is to establish the history of nuclear material of unknown origin by analysing the nuclear material in the laboratories. Hence, the results of the nuclear forensic examination will provide the evidence to support law enforcement or nuclear security investigation in the country. The typical analysis used in nuclear forensic investigation is radiological assessment, physical characterization, isotope analysis, elemental/chemical analysis and traditional forensic analysis. This paper will discuss the capability of laboratories in the Malaysian Nuclear Agency and internal arrangement in handling nuclear forensic analysis.