Nonproliferation Nuclear Forensics

LLNL-CONF-679869

I. Hutcheon, M. Kristo, K. Knight

December 3, 2015

Mineralogical Assocaition of Canada Short Course Series #43 Winnipeg, Canada May 20, 2013 through May 21, 2013 Disclaimer

This document was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor Lawrence Livermore National Security, LLC, nor any of their employees makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or Lawrence Livermore National Security, LLC. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or Lawrence Livermore National Security, LLC, and shall not be used for advertising or product endorsement purposes.

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CHAPTER 13: NONPROLIFERATION NUCLEAR FORENSICS

Ian D. Hutcheon, Michael J. Kristo and Kim B. Knight Glenn Seaborg Institute Lawrence Livermore National Laboratory P.O. Box 808, Livermore, California, 94551-0808, USA  e-mail: [email protected]

INTRODUCTION and age; these data are then interpreted to evaluate Beginning with the breakup of the Soviet Union provenance, production history and trafficking in the early 1990s, unprecedented amounts of route. The goal of these analyses is to identify illicitly obtained radiological and nuclear materials forensic indicators in the interdicted nuclear and began to be seized at border crossings and radiological samples or the surrounding international points of entry. The first instances of environment, e.g., container, transport vehicle or this new criminal activity, “nuclear smuggling”, packaging. These indicators arise from known were reported in 1991 in Italy and Switzerland and relationships between material characteristics and in subsequent years numerous incidents involving process history. Nuclear forensics requires a illicit trafficking of radioactive or nuclear material combination of technical data, relevant databases, occurred in a number of central European countries. and specialized skills and knowledge to generate, Between 1993 and 2011, the International Atomic analyze, and interpret the data. When combined Energy Agency (IAEA) recorded more than 2150 with law enforcement and intelligence data, nuclear incidents of illicit trafficking of radioactive material forensics can suggest or exclude potential origins (IAEA 2012) More than 400 of these incidents and thereby contribute to attribution of the material involve bona fide nuclear material, primarily to its source or production facility. depleted, natural or low-enriched uranium. Of A primary objective of nuclear forensics is to special concern, moreover, are the 16 or so events identify the source, or sources, of stolen or illicitly involving highly enriched U or Pu (Table 13-1). The trafficked nuclear materials and thereby prevent, or overt evidence of significant amounts of nuclear make more difficult, terrorist acts that would use material outside lawful control has created material from these same sources (Mayer et al. international concern over the importance of 2007, Moody et al. 2005). The perception of maintaining global nuclear order and underscores effective nuclear forensics is likely to deter some of U.S. President Obama’s statement in Prague in the individuals who would need to be involved in 2009, “In a strange turn of history, the threat of any act of nuclear terrorism and provides incentives global nuclear war has gone down, but the risk of to states to guard their materials and facilities better. nuclear attack has gone up.” The terrorist attacks on New York City and The new scientific discipline of Nuclear Washington, DC, on September 11, 2001, greatly Forensics was developed out of the need not only to increased the visibility of nuclear forensics, as identify and characterize illicit nuclear materials but policy makers worldwide became increasingly also to learn more about the original and intended concerned about the possibility of terrorist groups use of the material, its origin and the putative obtaining a nuclear weapon or using a radiological trafficking route. In the U.S., the nuclear forensics dispersal device (RDD or so-called “dirty bomb”). effort was jump-started by taking advantage of More recently, a consensus has developed among several decades of experience developed through international leaders that the threat of nuclear the nuclear weapons program, supplemented with terrorism poses a real and present danger to both expertise from geochemistry, material science and national and international security. U.S. President conventional forensics. Obama, the leaders of 46 other nations, the heads of Nuclear forensics is the technical means by the International Atomic Energy Agency and the which intercepted radioactive or nuclear material United Nations, and numerous experts have called (and any associated non-nuclear material) is nuclear terrorism one of the most serious threats to characterized to determine, for example, their global security and stability. The Communiqué of chemical and isotopic composition, physical state the 2012 Seoul National Security Summit

Mineralogical Association of Canada Short Course 43, Winnipeg MB, May 2013, p. xxx-xxx.

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TABLE 13-1: SELECTED INTERDICTIONS OF NUCLEAR MATERIAL Enrichment or 239Pu Year Location Type Mass content 1992 Augsburg, Germany LEU 2.5% 1.1 kg 1992 Podolsk, Russia HEU 90% 1.5 kg 1993 Vilnius, Lithuania HEU 50% 100 g 1993 Andreeva Guba, Russia HEU 36% 1.8 kg 1993 Murmansk, Russia HEU 20% 4.5 kg 1994 St. Petersburg, Russia HEU 90% 3.05 kg 1994 Tengen, Germany Pu 99.7% 6 g 1994 Landshut, Germany HEU 87.8% 0.8 g 1994 Munich, Germany Pu 87% 363 g LEU 1.6% 120 g 1994 Prague, Czech Republic HEU 87.8% 2.7 kg 1995 Prague, Czech Republic HEU 87.8% 0.415 g 1995 Prague, Ceske Budejovice HEU 87.8% 17 g 1995 Moscow, Russia HEU 20% 1.7 kg 1999 Ruse, Bulgaria HEU 72% 4 g 2001 Paris, France HEU 72% 0.5 g 2003 Ignalina, Lithuania LEU 2.0% 60 g 2003 Georgia/Armenia Border, Georgia HEU ~90% 170 g 2003 Rotterdam, Netherlands NU 0.72% 3 kg 2006 Tbilisi, Georgia HEU ~90% 80 g 2007 Pribenik-Lacacseke Border, Slovakia NU 0.72% 426.5 g 2010 Tbilisi, Georgia HEU >70% 18 g

Adapted from Kristo (2012). LEU, low enriched uranium; HEU, highly enriched uranium; NU, natural uranium; Pu, plutonium . recognizes that nuclear forensics can be an effective or radiological materials thoroughly in order to tool in the battle against global nuclear terrorism understand their origin and site of production, age, and encourages states to work with one another, as point of diversion, transit route, and intended end well as with the IAEA, to develop and enhance use. While nuclear forensics has been increasingly nuclear forensics capabilities and underscores the utilized to develop evidence for the potential importance of international cooperation both in prosecution of individuals who illegally possess technology and human resource development to nuclear materials, there is also increasing advance nuclear forensics (Communiqué 2012). recognition of the utility of nuclear forensics to Although the term “nuclear forensics” was provide an independent and objective measure of originally applied to the analysis of interdicted state declarations concerning nuclear capabilities, as nuclear materials in support of law enforcement, the well as application and intent. “Nonproliferation same analytical and interpretative capabilities used nuclear forensics” (NNF) supports international to examine interdicted samples may also be efforts to safeguard the nuclear fuel cycle by employed to investigate suspected proliferation at supplying information necessary to verify undeclared sites or to verify that declared nuclear declarations, e.g., compliance with the Nuclear programs are fully sanctioned (Dreicer et al. 2009, Nonproliferation Treaty, as well as attribute illegally Fedchenko 2007, 2008). The challenges posed by transferred materials. illicit trafficking and nuclear proliferation share the While robust nuclear forensic practices serve requirement to identify the characteristics of nuclear individual national security regimes within the

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context of illicit trafficking, the goals of include the application of modern material analysis nonproliferation nuclear forensics are global in techniques, knowledge of commercial and military scope and provide an international verification nuclear fuel cycles, and scientific principles to capability. NNF encourages governments to secure analyze unknown nuclear materials or devices and vulnerable inventories of nuclear materials and provide information of value to decision makers. deters nation states and organizations from This problem is complex enough before considering producing or transferring nuclear materials for the wide range of potential materials that may be malfeasant purposes. Illicit trafficking of encountered and the many different types of nuclear/radiological materials, investigations of information that potentially may be required. As in interdicted samples, and nuclear nonproliferation classical forensics, nuclear forensics relies on the and safeguards are inherently international fact that certain measurable parameters in a sample problems; no single country can hope to address are characteristic for a given material. Using these these critical 21st century issues, even on a local characteristic parameters, also known as scale, without global engagement. In this vein, many “signatures”, nuclear forensic analysis seeks to draw states have begun to develop international conclusions on the origin and intended use of the partnerships in nuclear forensics. In particular, intercepted material. global participation in the Nuclear Smuggling The technical response to specific nuclear International Technical Working Group (ITWG) has incidents requires a graded, iterative approach. led to the adoption of nuclear forensic best practices “Categorization” addresses the threat posed by multi-laterally in more than 30 states and specific interdicted material by identifying the risk international organizations (Niemeyer & Koch to first responders, law enforcement personnel, and 2002). The growing recognition of the importance the public. Following this step is an assessment to of international engagement to accomplish both determine if there is any indication of criminal nuclear nonproliferation and counter-terrorism activity or threat to national security. objectives underscores the need for a clearly “Characterization” provides a more thorough articulated approach to international engagement analysis of the material to determine the nature of that identifies and prioritizes foreign partners with the radioactive and associated, non-nuclear respect to access to the nuclear fuel cycle and joint evidence. “Interpretation” seeks to draw validated scientific endeavors. technical conclusions from the analytical results, The requirements of many national nuclear correlating the characteristics of the material with forensic programs exceed those of commercial and material production history. While interpretation is international verification regimes. Nuclear forensic the end product for the nuclear forensic laboratory, investigations require the sharing of validated the nuclear attribution process only begins at this protocols not only on major and minor isotopes, stage. Complete nuclear forensic analysis, therefore, chemical (trace element) compositions, and physical includes characterization of all materials, traditional forms (grain size, sorting, admixtures) of the forensic analysis, and interpretation. This approach, materials, but also concerning the processes used in predicated on the model action plan developed by facilities across the nuclear fuel cycle. Access to the Nuclear Forensics ITWG, is described in much this broad suite of information is critical to evaluate greater detail in the IAEA publication, “Nuclear the source and route of smuggled or proliferated Forensics Support,” Nuclear Security Series materials. There is also a compelling need to ensure Number 2 (Smith et al. 2008, IAEA 2006). that states conducting nuclear forensic measure- Nuclear forensic interpretation is a deductive ments – either independently or cooperatively – process (e.g., Fig. 13-1), much like the scientific have access to sufficient data for rigorous, high method itself. Initially, a hypothesis, or set of confidence, interpretation. The need to share data hypotheses, is developed based upon the initial may, by necessity, infringe on proprietary or analytical results. In most cases, the initial results national security information; these concerns must will be consistent with multiple hypotheses, which be addressed at the outset of any exchange and the may, in turn, suggest additional signatures. The potential to reveal specific capabilities or methods team then develops additional measurements to used by states as part of counter-terrorism and verify the presence or absence of the signatures. If nonproliferation programs may restrict an unfettered analyses show that the signature is absent, this exchange of information. hypothesis must be rejected or adjusted to fit the Basic challenges facing nuclear forensics new results. If, instead, the analyses confirm the

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nuclear forensic investigation may provide useful information only when combined with other, complementary results. Signatures for nuclear materials are intimately connected to the nuclear fuel cycle since each step in the fuel cycle (Fig. 13-2) both creates new signatures and erases or modifies some existing signatures. An on-going challenge for nuclear forensics is to validate signatures for each step in the fuel cycle and understand the processes that control a signature’s persistence. Almost without exception, a single signature is insufficient to answer all of the relevant questions. Independent signatures that reach the same conclusion increase confidence in the technical interpretation, while results that provide different or conflicting conclusions decrease the level of confidence. Nuclear forensic investigations are most successful when independent signatures representing a variety of material characteristics can

be linked and point toward a unique conclusion. Figure 13-1. Flow chart of the Nuclear Forensics analysis Figure 13-3 illustrates this process schematically by and interpretation process. depicting the universe of potential nuclear material signature, then either the investigation has come to a sources and processes. Each individual signature unique technical interpretation (i.e., the desired defines a subset of known materials from which an result) or additional tests to exclude other remaining intercepted sample may have originated. In the ideal hypotheses must be developed. In the ideal case, case, the use of multiple signatures leads to a unique only a single hypothesis or interpretation will point of intersection of multiple subsets correspond- eventually prove consistent with all results, although ing to a unique identification of the source and/or this is seldom true in practice. process. Signatures generally fall into two broad Signatures categories: comparative signatures and predictive The term “signatures” is used to describe signatures. Comparative signatures involve the material characteristics that may be used to link comparison of the measured properties (e.g., grain samples to people, places, and processes, much as a size, color, chemical and isotopic composition) of written signature can be used to link a document to an unknown sample (or “questioned sample” in law a particular individual. “Signatures” describe any enforcement parlance) to a similar set of properties characteristic or group of characteristics that can be for one or more reference samples. The critical used to help distinguish materials from one another question to be addressed is whether or not the or identify the processes history of a material. characteristics of an unknown sample are the same Signatures are essentially combinations of variables as, or at least are similar to, those of one or more of used to make comparisons. Some signatures, such as the reference samples. The use of comparative those associated with U or Pu isotopic analyses, signatures to identify an interdicted sample may may provide only general clues that serve to place involve either a point-to-point comparison or a the material in a broad category, e.g., Depleted point-to-population comparison. Point-to-point Uranium (DU) or Highly Enriched Uranium (HEU), comparisons are relatively rare and rely on the inter- or, perhaps, narrow the field of potential countries comparison of two or more closely matched of origin. Other signatures, such as characteristic samples, e.g., HEU samples interdicted in Bulgaria dimensions or markings, are generally applicable to in 1999 and in Paris in 2001 (Adamson et al. 2001, only a restricted class of materials, e.g., reactor fuel Baude 2008, Baude et al. 2008). Point-to-population elements or sealed sources, but may provide comparisons look for similarities between the valuable clues identifying a specific facility or date characteristics of an unknown sample and those of a of manufacture. In some cases, data generated in a population of potentially similar materials and are

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Figure 13-2. Representation of the nuclear fuel cycle, the progression of nuclear material through a series of stages beginning with the mining of ore; conversion to ore concentrate, UF6, and, finally, U oxide fuel; irradiation in a nuclear reactor; and reprocessing or disposition of spent nuclear fuel. The insets show representative images for different stages in the fuel cycle. more broadly applicable. Point-to-population Predictive signatures, in contrast, come into comparisons usually require access to databases play when representative data for a suite of containing information on hundreds or thousands of appropriate reference materials are unavailable. samples, or to nuclear forensic sample archives, Predictive signatures typically derive from which may contain tens or hundreds of physical underlying scientific principles, such as isotopic and samples. The value of the comparative approach chemical fractionation in the case of U ore and ore then depends strongly on the relevance and concentrate, neutron capture activation and fission coverage of the database and/or sample archive (see, in the case of nuclear reactor modeling, or e.g., Dolgov et al. 1999, Robel et al. 2009). radioactive decay in the case of age dating. Predictive signatures seek to calculate material characteristics useful for attribution based on a detailed understanding of the physical or chemical mechanisms responsible for producing the signatures. The advantage of the predictive approach is that the processes (and possibly locations) of unanalyzed nuclear materials can be inferred from their measured characteristics, something of critical importance for types of materials that are not readily available, e.g., materials from historical processes or tightly held materials from foreign countries. The disadvantage of the predictive approach is that significant effort must be expended to develop and validate the capability and to understand accurately the processes affecting signatures. Figure 13-3. Diagram showing how individual forensic New predictive signatures can also be signatures define the subset of materials from which an developed through advances in the understanding of interdicted sample may have originated. Applying the processes affecting chemical and isotope multiple signatures collectively increases confidence in distributions at the molecular, atomic and nuclear the assessment of identification of possible origins. scale. The 234U/238U ratio, for example, exhibits

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substantial variability in water, soil and sediment bulk constituents of a sample to assess the threat and U ore samples of different geographical origin posed by the material and confirm whether the (Gascoyne 1992). 234U is preferentially leached interdicted material is contraband; categorization compared with 238U from solids due to radiation forms the basis for continued investigation. damage of the crystal lattice from alpha decay of Categorization should occur on-site, at the point of 238U, oxidation of insoluble tetravalent 234U to interdiction and utilize non-destructive analytical soluble hexavalent 234U, and alpha recoil of 234Th techniques such as field-portable gamma-ray (and its daughter 234U) into fluid phases. Ores spectrometry, and hand-held X-ray fluorescence. leached by groundwater over long periods of time These nondestructive analyses can quickly dis- exhibit significant depletions in 234U, whereas ores tinguish between naturally occurring radioactive formed through deposition of those water leachates material, special nuclear material, radioactively exhibit complementary enrichment in 234U; the full contaminated material, or a commercial radioactive range in 234U concentration is nearly 20%. Modern source. mass spectrometry provides results of sufficient The goal of characterization is to determine precision and accuracy to allow small variations in the nature of the radioactive evidence. Character- the 238U/235U ratio, once thought to be invariant in ization provides full elemental analysis of the nature, to be measured. The depositional interdicted material, including major, minor and environment of an ore body appears to strongly trace constituents. For major constituents of the influence the 238U/235U ratio with low temperature radioactive material, characterization should also ores having systematically higher ratios than include determination of isotopic and phase (i.e., deposits formed at higher temperatures (Brennecka molecular) properties. Characterization also et al. 2010). In addition, naturally occurring includes measurement of physical properties, variations in 236U content can also be exploited as a including accurate measurement of critical nuclear forensic signature. Generally considered to dimensions of solid samples, determination of be an anthropogenic isotope, 236U is produced at particle size and morphology for powder samples, very low levels in U ore bodies through neutron and high magnification imaging of the material by capture on 235U; the abundance of 236U is strongly optical and scanning electron microscopy. influenced by the age of the ore body and the The goal of full nuclear forensic analysis is to volume of water in contact with ore (Tumey et al. (i) analyze all radioactive and traditional forensic 2009, Wilcken et al. 2008). All these features of the evidence, (ii) gather information to address isotopic distribution of natural U are potentially questions of material origin, method of production, useful (predictive) signatures for attribution of U ore loss of legitimate control, transit route from point of and ore concentrate. diversion to interdiction, and (iii) assess the likelihood that additional material is available. Full Nuclear Forensic Analysis. nuclear forensic analysis also includes detailed Nuclear forensic analysis does not lend itself to interpretation and often includes comparison of a simple “cook-book” approach, universally measured signatures against information contained applicable to all types of nuclear and radiological in nuclear forensics databases or sample archives or material. Instead, nuclear forensics involves an against predictive signatures generated by, e.g., iterative approach, in which the results from one reactor modeling, to assist in the identification of analysis are used to guide subsequent analyses. The the method of manufacture and most plausible international nuclear forensics community has source of the material. defined 3 levels of analysis – categorization, Nuclear forensics employs a wide array of characterization, and full nuclear forensic analysis – analytical tools to detect signatures in radioactive each of which serves a specific purpose in an material. The international nuclear forensics investigation. In all cases, though, sampling and community has achieved a general consensus on the analysis must be performed with due regard for proper sequencing of analytical techniques to preservation of evidence and chain-of-custody provide the most valuable information as early as requirements. Many of the analytical tools used in possible during an investigation. This consensus these analyses are destructive and consume some was achieved through discussions at meetings of the amount of sample during analysis. Proper selection ITWG, as well as the experiences of nuclear and sequencing of analyses is, therefore, critical. forensic laboratories in round-robin analyses. The The goal of categorization is to identify the ITWG and IAEA both recommend that the

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collection of time-sensitive or environmentally nuclides of potential interest such as 14C and 3H) sensitive samples should occur within the first 24 undergo β-decay without accompanying photon hours after interdiction. Non-destructive analysis emission. should be conducted before destructive analyses Gamma spectroscopy has a dual role in nuclear whenever possible. Table 13-2 shows the generally forensics. It is the first technique that is used when accepted sequence of analysis, broken down into interdicted nuclear material is investigated. Since techniques that should be performed within 24 gamma rays are only slightly attenuated by hours, 1 week, or 2 months after interdiction. Table packaging material (unless shielding like lead is 13-3 provides an overview of many analytical used), initial measurements in the field (e.g., at techniques commonly used in nuclear forensic border-crossing stations) carried out with simple, investigations; additional information may be found portable gamma spectrometers provide rapid and in (Moody et al. 2005). accurate categorization of the material. For example, it is possible to distinguish between naturally Radiometric Techniques measure the radiation occurring radioactive material, radioactive source, emitted by radioactive nuclides during decay to a medical isotopes or anthropogenic nuclear material. daughter nuclide. There are three types of radiation In laboratories, more sophisticated high-resolution commonly encountered in nuclear forensics – alpha, gamma spectrometers (HRGS) are used. Their beta and gamma radiation, each with its own energy resolution is much better compared to the properties and methods of detection. Most heavy portable instruments, allowing gamma rays with nuclides (e.g., U and Pu) decay by emitting an alpha energies very close to each other to be resolved. particle. Gamma radiation is also often emitted HRGS provides an initial determination of the after the alpha decay to bring the daughter nuclide isotopic composition of U and/or Pu, as well as from an excited state to the ground state. Each detection and quantification of trace fission and nuclide emits characteristic gamma rays with activation products. It should, however, be noted energies specific to an individual radioisotope. that some nuclides like 242Pu or 236U cannot be While useful for characterizing the performance of detected by gamma spectroscopy. In these cases, chemical separations in the laboratory, β mass spectrometry offers a useful alternative. spectrometry is rarely employed as a quantitative Alpha spectroscopy is used to quantify the technique. Most β-emitting radionuclides also emit γ abundance of α-emitting radionuclides, particularly rays characteristic of the decaying nuclides; those with relatively short half-lives. Alpha particles however, a few radionuclides (including long-lived are stopped for example by a paper sheet, because fission products such as 99Tc and 147Pm and other

TABLE 13-2. TIME LINE OF ANALYSES IN NUCLEAR FORENSIC ANALYSES Techniques/Methods 24 hour One week Two months Radiological Estimated total activity Dose rate (α, β, γ, n) Surface contamination Physical Visual inspection characterization Raadiography Photography Weight Dimensions Optical microscopy Density Traditional forensic Fingerprints, fibers analysis Isotope analysis γ-spectroscopy Mass spectrometry Radiochemical α-spectroscopy (SIMS, TIMS, ICP– separations MS) Elemental/chemical ICP–MS GC/MS XRF Assay (titration, IDMS)

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TABLE 13-3 EXAMPLES OF ANALYTICAL TOOLS FOR NUCLEAR FORENSICS Measurement Technique Type of Typical detection Spatial goal information limit resolution Survey HRGS Isotopic ng – μg Elemental and Chemical Assay Elemental mg Isotopic Radiochemistry/Radiometric Isotopic, fg – pg

Bulk Analysis Methods Elemental TIMS Isotopic, pg – ng

Elemental ICP–MS Isotopic pg – ng

Elemental XRF Elemental 10 μg/g XRD Molecular ~1 at.% GC/MS Molecular μg/g Imaging Visual Inspection Macroscopic 0.1 mm Optical Microscopy Microscopic 1 μm Structure SEM 1 nm TEM 0.1 nm Microanalysis SIMS Elemental 0.1 ng/g – 0.1 – 1 μm Isotopic 10 μg/g SEM/EDS or WDS Elemental 0.1 – 1 wt.% 1 μm FTIR Molecular 0.1 – 1 wt.% 10 μm Raman Molecular ~1 wt.% 1 μm mg =milligram = 10–3 gram at.% = atom percent μg = microgram = 10–6 gram wt.% = weight percent ng = nanogram = 10–9 gram ppm = parts per million by weight pg = picogram = 10–12 gram ppb = parts per billion by weight fg =femtogram = 10–15 gram μm = micrometre = 10–6 metre HRGS = High-Resolution Gamma Spectrometry SEM = Scanning Electron Microscopy TIMS = Thermal Ionization Mass Spectrometry TEM = Transmission Electron Microscopy ICP–MS = Inductively Coupled Plasma Mass Spectrometry SIMS = Secondary Ion Mass Spectrometry XRF = X-ray Fluorescence Analysis EDS = Energy Dispersive Spectroscopy XRD = X-ray Diffraction Analysis WDS = Wavelength Dispersive Spectroscopy GC/MS = Gas Chromatography/Mass Spectrometry FTIR = Fourier Transform InfraRed Spectroscopy of their strong interaction with matter. used to calculate the date of the last Pu purification Consequently, an alpha measurement through performed on a sample and 230Th (daughter of 234U), packaging material or shielding is impossible. to determine a last purification date for U materials. Unlike γ-spectroscopy, α-spectrometry is a destructive technique requiring rather laborious Mass spectrometry Mass spectrometric techniques sample preparation. Source preparation is crucial for make use of small mass differences between achieving good energy resolution in α-spectroscopy nuclides. In mass spectrometry the atoms contained and target elements are usually separated and in a sample are converted to ions and then separated purified before being deposited onto a flat surface. according to their respective mass to charge ratios Quantification is achieved by spiking the samples and the intensities of the mass-separated ion beams with known amounts of an isotopic spike or tracer. measured. Mass spectrometry is used to determine Alpha spectrometry is especially suited for both the elemental and isotopic compositions of quantifying 232U and 238Pu due to their short half- nuclear materials, providing extremely high lives and, in the case of 238Pu, the potential precision and accuracy, as well as the capability to interference from 238U in mass spectrometry. Alpha analyze both radioactive and stable isotopes. Mass spectrometry is also used to quantify 241Am spectrometry can quantify elemental concentrations (daughter of 241Pu), whose concentration can then be either by using an isotopic spike (isotopic dilution

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mass spectrometry) or through calibration against powerful and widely applied method for quantifying standards. Nuclear forensic analysis utilizes a trace element abundances. The minimum detection variety of different types of mass spectrometers, limit for MC–ICP–MS is typically <1 pg/g and can differing primarily in the way ions are generated and attain the fg/g range for favorable elements. whether samples are introduced as liquids, gases or Laser ablation inductively coupled plasma mass solids. One important exception is accelerator mass spectrometry (LA–ICP–MS) uses a high energy spectrometry, which accelerates ions to MeV light source and laser ablation cell and to supplant energies rather that the keV energies used in most the spray chamber/nebulizer of a standard ICP–MS mass spectrometers. instrument. Material is ablated from a sample using In Thermal Ionization Mass Spectrometry a pulsed laser (often a Nd-YAG tuned to 266 or 213 (TIMS), samples consisting of small (~fg–μg) nm) and transported in an inert gas stream (typically quantities of chemically separated and purified He or Ar) to the plasma torch for ionization and analytes dissolved in a small volume (typically 1–10 subsequent mass analysis as per solution ICP–MS. ml) are deposited on a refractory metal filament LA–ICP–MS analyses require minimal sample (e.g., high purity W or Re) and evaporated to preparation. While laser spot sizes can be reduced to dryness. The filament is then heated to temperatures several micrometres, sensitivity is degraded, and of 1,000–2,500°C in the ion source by resistive spatial resolution is typically ~10–100 μm. Matrix heating or electron bombardment. If the ionization matched standards are preferred (but not always potential of the analyte is low compared to the work required) for accurate trace element and isotope function of the filament, a fraction (typically <1%) analyses in LA–ICP–MS. Depending on the quality of the analyte atoms will be ionized and emitted of standards, LA–ICP–MS accuracy for trace from the filament surface. Multi-collector TIMS element abundances is typically 1–10% with limits instruments, employing multiple detectors able to of detection in the ng/g range. The combination of measure over a dozen isotopes simultaneously, are laser ablation and MC–ICP–MS is capable of capable of measuring differences in isotope producing data with much higher precision and abundance ratios as small as a few parts in 106. accuracy (e.g., Arevalo et al. 2010). TIMS is the preferred technique for measuring Sr, Secondary ion mass spectrometry (SIMS) is a Nd, U and Pb isotopes with the highest possible microanalytical technique applicable to samples precision and accuracy. A disadvantage of TIMS is ranging in size from centimetres to submicrometre the laborious sample preparation. As in the case of particles and providing both elemental and isotopic α-spectrometry, samples need to be dissolved and information. SIMS uses a finely focused primary ion + – + + chemically purified to avoid mass interferences and beam, e.g., O2 , O , Cs , or Ga , to sputter the achieve high sensitivity, accuracy and precision. sample surface, producing secondary ions that are In many laboratories TIMS has been then analyzed by a mass spectrometer. SIMS is supplemented by multi-collection inductively capable of acquiring microscopic images of isotopic coupled plasma source mass spectrometers (MC– and elemental distributions with spatial resolution ICP–MS). For solution mode MC–ICP–MS, a exceeding 50 nm and can be used to measure the chemically separated and purified sample containing concentration of any element, from H to Pu, with a the element of interest is dissolved in an acid dynamic range of more than nine orders of solution, which is converted into an aerosol spray magnitude in concentration. SIMS is applied in using a nebulizer and subsequently aspirated into an nuclear forensics when only small amounts of Ar-based plasma. The analyte dissociates into sample are available or when the sample is atomic constituents and ionizes in the high inhomogeneous and spatially resolved analyses are temperature plasma (5,000–8,000 K) with very high required. The sputtering process is highly matrix- efficiency (>90% for elements with a first ionization dependent and accurate quantitation requires matrix- potential of <8 eV). The salient features of ICP–MS matched standards. The accuracy is typically 0.1– are multi-element capability, high sample through- 0.5% for isotope ratio measurements and 2–10% for put, good sensitivity and large dynamic range. trace element measurements. SIMS is the technique Multi-collector instruments provide isotope of choice to determine isotope ratios and trace measurements with high precision and accuracy for element abundances in particulate samples. Using a a variety of elements across the periodic table sharply focused primary ion beam, SIMS can including Mg, Fe, Mo, Hf, Pb, U and Pu. In addition analyze particles in the μm-size range, weighing <1 to measuring isotopic compositions, ICP–MS is a pg, with a precision and accuracy of better than

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0.5%. In many nuclear forensic applications, a few instrument used to examine a sample in detail, and U- or Pu-bearing particles may be immersed in a sea allows the forensic scientist to answer the simple, of environmental detritus containing little forensic yet vital, question, “what does the sample look information. SIMS can be used in particle-search like?” before proceeding with more extensive, and mode to locate and analyze these rare, but highly often destructive, analyses. Optical microscopy valued, particles. As with laser ablation ICP–MS, reveals details of color, surface morphology and the adoption of large geometry, multi-collector mass texture, shape and size, tool marks, wear patterns, spectrometers has significantly improved SIMS surficial coatings, corrosion, and mineralogy (Grant capabilities, particularly for determination of low- et al. 1998, Moody et al. 2005). The stereomicro- abundance isotopes like 236U (e.g., Ranebo et al. scope produces three-dimensional images at 2009). relatively low magnification (~2–80 ×) and is very Gas chromatography–mass spectrometry (GC– useful for dissecting or aliquoting samples for MS) is a technique for detecting and measuring additional analyses. The polarizing microscope trace organic constituents in a bulk sample. In GC– passes light through a set of polarizing filters to gain MS, the components of a mixture are separated in a additional information about the sample from gas chromatograph and identified in a mass optical properties such as crystallinity, anisotropy, spectrometer. The primary component of a GC is a pleochroism and birefringence; polarizing narrow-bore tube maintained inside an oven. In the microscopes can readily magnify an image to simplest arrangement, the analyte mixture is flash- 1000 ×. The limit of resolution is set by the vaporized in a heated injection port. The various wavelength of light used to illuminate the sample; components are swept through the column by a the theoretical resolution limit of conventional carrier gas for separation based upon relative microscopes is 200 nm, but values closer to 1 μm absorption affinities. In an ideal case, components are more commonly achieved. elute from the column separated in time and can be In Scanning Electron Microscopy (SEM), a introduced into the mass spectrometer as a time finely focused electron beam is rastered over a series. The mass spectrometer detects and quantifies sample and the interaction of the incident electron the concentration of each component as it elutes beam with the sample produces a variety of signals: from the column. GC–MS analyses provide very back-scattered electrons, secondary electrons, Auger high specificity, allowing extremely complex electrons, X-rays, and photons. By measuring the mixtures to be accurately separated and individual intensity of one or more of these types of particles species to be identified accurately. Limits of as a function of raster position, an image of the detection for scanning GC–MS are on the order of sample is constructed. Each type of emitted particle ng of material, corresponding to sensitivities of ~1 conveys different information about the sample, part in 1013 for simple samples and 1 part in 1011 for and, by choosing the appropriate detection mode, complex mixtures. either topographic or compositional contrast is revealed in the image. Secondary electrons arise Imaging Techniques The role of microscopy is to from inelastic collisions between incident electrons provide a magnified image of a sample, allowing the and atomic electrons within the outer few nm of the observation of features beyond the resolution of the surface and carry information about sample unaided human eye (roughly 50–100 μm). The topology (e.g., Fig, 13-4). Back-scattered electrons, ability to identify and characterize diverse suites of in contrast, have energies comparable to the incident samples rapidly and without compromising the electron beam, carry information about the mean integrity of the sample is an essential starting point atomic number and can be used to construct maps of of most forensic investigations. A variety of the distribution of phases with disparate chemical microscopy techniques are applied in nuclear composition. With thermionic, W filament sources, forensic science, using photons, electrons, and image resolution is limited to ~10 nm, with a X-rays to probe the physical, chemical, and corresponding maximum magnification of 100,000. structural make-up of samples at spatial scales With field-emission electron sources, the resolution ranging from nanometres to centimetres. exceeds 1 nm with a corresponding maximum Optical microscopy dates back more than 300 magnification of 1,000,000. years and remains one of the most basic and Transmission electron microscopy (TEM) lies fundamental characterization techniques in nuclear at the opposite end of the spectrum from optical forensics. The optical microscope is often the first microscopy – difficult to use and requiring elaborate

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most solid samples, including micrometre-size particles. Characteristic X-rays can be analyzed by one of two methods. An energy-dispersive X-ray spectrometer (EDS) uses the photoelectric absorption of X-rays in a semiconductor detector, usually Si(Li), to measure the energy and intensity of incident X-rays simultaneously. EDS systems provide an easy-to-use method of measuring X-ray spectra over a broad energy range and can detect elements from B to U. Detection limits are typically ~0.1% for silicate and oxide materials. A wavelength-dispersive spectrometer (WDS) operates on the principle of Bragg diffraction; X-rays are dispersed according to wavelength, rather than Figure 13-4. SEM photomicrograph of plutonium oxide. energy. WDS provides much higher energy The variety of morphologies suggests the sample is a resolution and sensitivity (~10 ×) compared to EDS mixture of materials produced under different and can detect elements from Be to Pu, with conditions. detection limits of 0.01%. X-ray microanalysis is particularly valuable in nuclear forensic sample preparation. Its unique capabilities for ultra- investigations for the speed with which X-ray high spatial resolution and for revealing intensities can be accurately quantified to yield microstructural information, however, make the elemental concentrations in interdicted samples. TEM an important tool in many nuclear forensic investigations. In TEM, a high-energy electron Other techniques. X-ray diffraction (XRD) is the beam is transmitted through a very thin sample standard method for identifying the chemical (<300 nm thickness). In imaging mode TEM structure of crystalline materials. A collimated beam produces a magnified image of the sample providing of X-rays impinging on regularly ordered lattices information on thickness, crystallinity, crystal undergoes constructive and destructive interference orientation, defects and deformations. Under- depending on the spacing of the lattice, the standing how contrast is generated is key to wavelength of the X-rays, and the angle of distinguishing among these competing effects and incidence of the X-ray beam. By rotating a sample presents a significant challenge in image relative to a fixed X-ray source, variations in interpretation. The diffraction mode provides an interference lead to characteristic diffraction electron diffraction pattern, analogous to an X-ray patterns. These diffraction patterns can be compared diffraction pattern. Electron diffraction patterns can to reference spectra to identify specific crystalline be indexed by the same procedures used in X-ray phase. XRD is not applicable to amorphous (non- diffraction and used to identify phases on an crystalline) materials. extremely fine spatial scale. Just as in SEM, X-ray fluorescence (XRF) provides non- characteristic X-rays are generated by the destructive quantification of chemical concen- interaction of the electron beam with the sample. X- trations in both solid samples and solutions for ray analysis can be combined with TEM imaging elements from Mg to Pu. A beam of high energy and diffraction to provide comprehensive X-rays excites characteristic secondary X-rays information on a specimen’s internal microstructure, whose intensities are quantified using a wavelength- with nm spatial resolution. TEM is capable of an or energy-sensitive detector. The detection limits for extremely wide range of magnification (from ~ 50 × XRF are generally in the range of tens of μg/g, to several million ×) and is able to image extremely although actinide matrices generate many X-rays fine structural detail, but at the expense of severe that interfere with the lower energy X-rays of lighter restrictions on sample thickness. elements, potentially decreasing signal-to-noise The characteristic X-rays generated by ratios and increasing detection limits. Wavelength interactions between energetic electrons and the dispersive analysis (WDS) provides higher energy sample in SEM or TEM carry information on resolution than energy dispersive analysis (EDS), chemical composition and provide an important and is capable of resolving some of these method to determine elemental concentrations for interferences. XRF is often used as a screening tool

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in nuclear forensic analyses to guide additional the chronometers should yield the same age. analyses using mass spectrometry. However, while the 232U–236Pu, 234U–238Pu, 235U– Infrared Spectroscopy (IR) is useful for the 239Pu and 236U–240Pu chronometers all yield the identification of organic compounds. Through the same age in most U.S. weapons grade Pu metal use of an infrared microscope, IR can be performed samples, 241Am–241Pu often gives a significantly on samples as small as 10 μm and is an important larger value. This discordance indicates that when U microanalytical technique in nuclear forensics. was last removed from the Pu, some Am was left Molecular bonds vibrate at characteristic behind. As a result, there will be more 241Am in the frequencies and if a particular molecular vibration sample than can be explained by in-growth, results in a change in a bond’s dipole moment, the resulting in an apparent age that is too large. An molecule will absorb infrared radiation example of the application of several radio- corresponding to that characteristic frequency. In chronometers to HEU and the ability to tightly IR, a sample is irradiated with a broad band of constrain the sample age is contained in the infrared frequencies and the intensity of the discussion of the Bulgarian seizure below. reflected or transmitted radiation is measured as a function of frequency. Absorption at specific Case Studies frequencies is characteristic of specific bonds and The ultimate test for protocols developed in the the IR spectrum identifies the various bonds and laboratory in a controlled environment is posed by functional groups within the molecule. Extensive their application to real world samples, obtained libraries of IR spectra help identify unknown under uncontrolled conditions and whose properties compounds but unambiguous identification usually often contain unexpected features. Case studies are requires an additional analytical technique, such as normally conducted in cooperation with government mass spectrometry or NMR. or law enforcement agencies with responsibility for sample collection. The agency responsible for Chronology. Radionuclides linked to one another by collecting the sample works with the nuclear radioactive decay have relative concentrations that forensic scientists to develop a Statement of Work can be calculated by the simple laws of radioactive (SOW) specifying the material properties to be in-growth or, in more complicated cases, by the measured. In most cases the SOW follows the Bateman equations. The measurement of the relative nuclear forensics Model Action Plan described in concentrations of parent and daughter isotopes IAEA Nuclear Security Series #2 (IAEA 2006). The provides a direct measure of the time since the SOW also lays out the time lines for analysis and daughter radionuclides were last removed from the reporting of final results. respective parent isotopes. In nuclear forensic investigations, the interval between the time a TABLE 13-4. ABUNDANCES OF HEAVY-ELEMENT sample was purified and the time it was DAUGHTER NUCLIDES IN A 1 G SAMPLE OF PU subsequently analyzed is defined as the “age” of the METAL material (Moody et al. 2005, Mayer et al. 2005). Half-life Mass Activity The presence of both U and Pu provides the Nuclide opportunity to measure the age of a sample through (Myr) (ng) (dpm) 230 -3 as many as a dozen different chronometers. If the Th 0.075 1.3 x 10 0.06 ages given by different chronometers “agree” with 231Pa 0.033 1.3 x 10-5 0.0013 each other (concordant ages), then we have high 233 -5 U 0.16 5.6x 10 0.0012 confidence the assumptions for accurate age-dating 234 are satisfied and the model ages reflect the time U 0.25 915 12700 since purification. If the chronometers do not agree 235U 704 26300 126 with each other (discordant ages), caution must be 236U 23.4 6250 897 exercised in the way model ages are interpreted, as 238 -4 they may fail to indicate accurately the time since U 4470 0.42 3.2 x 10 purification. Table 13-4 lists the quantities of heavy- 237Np 2.14 355 555 element daughter nuclides present in a 1 gram 241Am 4.32 x 10-4 427000 3.3e9 sample of weapons grade Pu after an in-growth Sample contains 6% 240Pu, 0.91% 241Pu, and 0.023% period of one year. If the sample was completely 242Pu, after 1 year of in-growth. purified during the last chemical separation, all of

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Counterweight – A Nuclear Smuggling Hoax. A was most plausibly a piece of an aircraft dense, dark gray ~9 kg metal sample was involved counterweight assembly, most plausibly from a U.S. in a sale of illicit nuclear materials in Hong Kong in military aircraft. 1988. The sample was originally offered for sale as In the nuclear smuggling world, this sample “nuclear weapon-useable material” by a Southeast was one of the earliest contraband items in what Asian military official and then subsequently ultimately became known as the “Southeast Asian rediscovered in a U.S. consulate nearly 10 years Uranium” scam. This hoax was a pervasive swindle, later. Lawrence Livermore National Laboratory first reported in 1991, and especially prevalent in (LLNL) was contacted with a request for forensic Thailand, Vietnam, and Cambodia. Transactions of characterization (a photograph of the sample may be irregularly shaped metal parts, alleged to be 235U, found in Grant et al. 1998). with asking prices of ~$10,000 per item, are not HRGS analysis revealed that the main uncommon. Similar material has also been used for radioactive component of the specimen was U, barter as substitute currency in drug-trafficking considerably depleted in 235U. Bulk analysis of the operations. sample yielded a density of (17 ± 0.3) g/cm3, some- what less than the theoretical density of U metal. High Enriched Uranium Interdicted in Bulgaria. The reduced density of the part suggested that voids Just after midnight on 29 May 1999, a Turkish could be present or that it was composed of two or citizen, Urskan Hanifi, was stopped at a border more inhomogeneous phases. crossing in Ruse, Bulgaria, on his way into After consultation with the collecting agency, Romania. Although claiming to be returning from the sample was characterized using radiochemical an extended trip to Turkey, the Bulgarian border analysis, electron microprobe, SIMS, ICP–MS and guard became suspicious because the car’s interior XRF. The results showed that the material was was very tidy and appeared to contain no luggage. A depleted U containing ~0.3 wt.% 235U and was a search of the car turned up a certificate for the metal alloy of 90% U with 10% Mo. The sample purchase of “99.99% uranium 235” written in was coated with electroplated Ni ranging in Cyrillic and a lead container labeled “uranium 235” thickness between 85 to 150 μm. The crenulated concealed inside an air compressor in the trunk of outer margin implied that the piece had been cast the car. Inside the container was a glass ampoule and then not machined prior to Ni plating. Radio- filled with several grams of fine black powder that chronometry based on 234U–230Th determined the Bulgarian scientists confirmed to be highly enriched date of last chemical purification as 1961 (± 3 uranium (Fig. 13-5). Hanifi then tried to bribe the years). customs officials, who, to their credit, refused his Once the nuclear forensic information was money and instead arrested him. According to press collected, LLNL carried out a complementary reports, Mr. Hanifi, told police he had purchased the investigation using conventional forensics and uranium in Moldova and had been trying to sell it in determined the part had been made by the National Turkey; having failed, he was attempting to return Lead Company of Albany, NY and then transferred to Moldova. to Nuclear Metals, Inc. The interdicted specimen

Figure 13-5. Photomicrograph of the HEU interdicted in Bulgaria in 1999. The left image shows the Pb container with its distinctive yellow wax lining, while the right image shows the HEU powder inside the glass ampoule. (Reproduced from Adamson 2001).

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Roughly one year after the U-filled vial was frequency analysis of grains showed a wide seized in Bulgaria, the U.S. Dept. of State arranged distribution of sizes, spanning the interval from 30 for it to be sent to Lawrence Livermore National to 550 nm, with a mean diameter of only ~160 nm. Laboratory with the hope that detailed analyses The abundance of very small grains with diameters could offer clues to the material’s origin. Over the of <300 nm, provided an important clue to the next 9 or so months, a team of nuclear forensic manufacturing process used to make the HEU, as scientists from LLNL and several other Dept. of such small sizes are difficult to generate by Energy laboratories performed an exhaustive study mechanical grinding and milling. of the HEU and the associated packaging materials, The concentrations of 72 elements, ranging revealing a wealth of information that ultimately led from Li to Th, were measured using a variety of investigators to the source of the HEU (Adamson et analytical techniques. Individual elements vary al. 2001). widely in concentration, from <2 ng/g to ~200 μg/g. Following an initial evaluation by HRGS, The total impurity inventory, 500 to 800 μg/g, is revealing that the HEU contained ~72% 235U, 1% high compared to other HEU samples, with 4 234U and no significant Pu, the sample and elements (Cl, S, Fe, and Br) accounting for ~60% of packaging materials were characterized using the total inventory. The enrichment of the volatile, optical microscopy, SEM and TEM, both with electronegative elements, S, Cl, and Br, is most energy dispersive X-ray analysis, XRD, radio- readily interpreted as a signature of chemical chemistry followed by α- and γ-spectrometry and reprocessing. Overall, the trace element abundances mass spectrometry, optical emission spectrometry, are much higher than expected for laboratory scale ion-, gas- and gel- permeation chromatography, reprocessing and suggest the HEU is an aliquot of GC–MS, IR spectrometry, X-ray photo-electron batch reprocessing. spectroscopy, and XRF. The concentrations of 35 radionuclides, The HEU is a very fine-grained powder spanning 15 orders of magnitude in concentration, composed predominantly of U3O8. The powder were determined by α- and γ-spectrometry following formed loosely compacted clumps ranging to 100 radiochemical separation. The major constituents μm in size. Individual particles are irregularly are the six U isotopes – 238U, 236U, 235U, 234U, 233U, shaped and distinctive morphologies are absent at and 232U – plus 230Th (produced by decay of 234U); the resolution provided by the SEM. TEM 241Am, five Pu isotopes – 242Pu, 241Pu, 240Pu, 239Pu, performed on an aliquot of the sample revealed two and 238Pu – 237Np and the fission products – 125Sn, distinctive classes of particles. Equant to slightly 134Cs, and 137Cs – were also detected. The presence ovoid grains dominate the population, comprising of the three fission products provides incontro- ~90% of the total, with rod-shaped and plate-shaped vertible evidence the sample is reprocessed U, grains making up the remainder (Fig. 13-6). A size– irradiated in a nuclear reactor.

Figure 13-6. TEM photomicrograph of the HEU seized in Bulgaria revealing two distinctive shapes of grains – oval to equant grains making up ~90% of the sample (left-hand image) and much rarer, elongated, rod- or plate-shaped grains (right-hand image). Both types of grains are U3O8. The scale bars represent 300 nm in the left-hand image and 100 nm in the right-hand image. (Reproduced from Adamson, 2001).

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The isotopic composition of U was determined Collateral Evidence. The Pb container was by three different techniques – SIMS, TIMS, and examined via optical and scanning electron MC–ICP–MS – and the Pu isotopic composition microscopy. Marks on the outer surface provided was determined by TIMS. SIMS provided a rapid clear evidence of coarse filing by hand for shaping (within 24 hours of sample aliquoting), reasonably and smoothing; marks indicative of the use of accurate, initial analysis of the major U isotopes. machine tools are absent. The overall appearance of TIMS and MC–ICP–MS provided data on all six U the container, especially the irregular form, suggests isotopes, including the low abundance isotopes 232U the container was cast in a crude sand mold and and 233U, with much higher accuracy than SIMS or shaped by hand. This supposition was later HRGS. The analyses by all of the instrumental confirmed by metallurgical examination. methods yielded a consistent U isotopic composition A small fragment was cut from the container, for the HEU powder, notable especially for the polished, and etched to reveal the microstructure. extremely high 236U content. These data are sum- The structure, consisting of Pb dendrites surrounded marized in Table 13-5. The U isotope abundances by a two-phase eutectic region, is characteristic of identify the material as HEU containing ~73% 235U, common, cast Pb metal. SEM/EDS showed ~5 wt.% i.e., weapon-usable material. The U isotope abund- Sb had been added to the Pb to produce an alloy ances suggest an initial enrichment of ~90% and the with greater malleability. The SEM also revealed high concentration of 236U indicates a prolonged remnants of an aluminosilicate, similar to kyanite irradiation history. The isotopic composition of Pu (Al2SiO5), trapped in the Pb. Kyanite, a naturally is consistent with weapon-useable material but the occurring mineral, is commonly used for high- concentration (~2 ng/g) is much too low for the temperature insulation and may have been used as a HEU to be a significant source of weaponizable Pu. mold wash, liner, or release agent in the casting The age of the sample was determined using process. nine radio-chronometers, based on the decay of U The yellow wax filling the interior of the Pb and Pu. The mean age of the HEU was 6.5 y, container was analyzed by Fourier transform infra- relative to the date the radiochemical separation was red spectrometry to identify molecular compounds. carried out at LLNL, 17 April 2000, indicating the Based on FTIR spectra, the wax was identified as a HEU was reprocessed on 30 October 1993 with an paraffin derivative with composition inconsistent uncertainty of <1 month. The agreement in age for with many commercial waxes but strikingly similar the nine radio-chronometers indicates that the trace to the paraffin-based wax, Parowax®. The coloring level of Pu in the sample was introduced during agent was identified using methylene chloride to reprocessing and is not a recently added extract the paraffin from the inorganic component contaminant. The ability to determine sample age and then XRF to examine the residue. XRF with high accuracy is significant from a Safeguards identified the inorganic residue as Ba chromate perspective. In principle, if the HEU had been (BaCrO4), once commonly used as yellow pigment diverted from a facility subject to International in paints, glass, and ceramic over-glazes, as an Atomic Energy Agency oversight, and if oxidizer in pyrotechnics, and as an oxidizer in heat reprocessing records were complete, the identity of powders and igniters. Barium chromate is rarely the sample could be determined on the basis of the used today in the U.S. or most western countries accurate age determination alone. because of environmental and health concerns but widespread use persists in Brazil, China, India, and TABLE 13-5. URANIUM ISOTOPE ABUNDANCES IN eastern European countries. HEU INTERDICTED IN BULGARIA The two paper samples retrieved from the Pb Isotope Abundance (atom %)1 container were characterized using forensic micro- 232U (1.06 ± 0.06) x 10-6 scopy to determine the composition of the wood 233 -5 fibers making up the paper. The quality of the paper U (3.0 ± 0.18) x 10 is similar to commercial office paper. Fibers from 234U 1.175 ± 0.003 the inner paper liner separating the ampoule from 235U 72.657 ± 0.012 the paraffin wax consisted of 61% bleached soft- 236U 12.133 ± 0.004 wood and 39% bleached hardwood, while fibers 238 from the label removed from the cap on the shield U 14.045 ± 0.011 consisted of 38% bleached softwood, 23% semi- 1 Uncertainties are 2 standard deviations. bleached softwood and 39% bleached hardwood.

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Both the softwood and the hardwood fibers were reactor, possibly a pressurized water reactor, test produced with the Kraft pulping process. The fibers facility, a research reactor for naval propulsion in these papers are not found in North America, systems, or a materials test reactor. The low Western Europe, or Scandinavia and the two paper abundance of 241Pu suggests the fuel was stored for samples were most plausibly produced in Eastern 10–20 y after discharge before reprocessing. Europe. The data for the non-nuclear samples reinforces the assertion that the sample originated in the former Nuclear Forensic Interpretation. The primary goal Soviet Union. The ampoule has been identified by of nuclear forensic interpretation is to identify the visitors to FSU nuclear facilities as strongly original source of the material, the intended, or resembling the glass containers used to preserve original, use, and the responsible individual or aliquots of production runs for archival material. organization. Typically, interpretation proceeds in The Ba chromate giving the wax its distinctive stages, focusing first on unambiguous signatures yellow color is banned in the U.S. and most Western (e.g., U isotopic composition), then proceeding to countries but is still widespread in Brazil, China, more subtle signatures (e.g., trace elements and India and many of the Newly Independent States. physical properties), and finally considering The paper products are derived from mixtures of collateral signatures found, e.g., in packaging. The hardwood and softwood trees not found in the U.S. dominant signature of the HEU is the U isotopic or Western Europe, but common in Eastern Europe. composition. The U isotope abundances, especially Finally, the Pb isotope composition of the container the unusually high concentration of 236U, clearly is inconsistent with Pb mined in the U.S. but indicate the sample is HEU irradiated and then compatible with lead from Asia or Eastern Europe. reprocessed reactor fuel. The HEU had an initial The preponderance of the evidence thus points 235U abundance of ~90%, immediately excluding to an origin in the FSU. Efforts to refine this material manufactured in the United States, since attribution analysis are continuing, including recent most U.S. HEU has a 235U content of ~93%. The efforts to compare the characteristics of the HEU 90% enrichment is consistent with HEU produced in seized in Bulgaria with similar material interdicted the one of the states of the former Soviet Union in Paris (Baude 2008, Baude et al. 2008). (hereafter, FSU). Recent interdictions (Sokova & Potter 2008, Other characteristics of the fuel and packaging Global Security Newswire 2010, 2011) suggest that also point to an origin in the FSU. The grain size is attempts to smuggle weapon-useable nuclear characteristic of material prepared for specialized materials across international borders still continue. use, e.g., powder metallurgy. The extremely fine Illicit trafficking in nuclear materials remains an grain size of the powder is unlike that found in U.S. important area of concern for the International facilities, where coarser sizes are used to minimize Atomic Energy Agency, Europol, and national law the health hazard created by respiration of fine dust. enforcement agencies, and has gained increased The HEU has the characteristics of feedstock for attention in the context of recent Nuclear Security fabrication of fuel pellets and blending with other Summits. batches of U oxide at U fuel conversion facilities in the FSU. Multiple samples, similar to the one CONCLUSIONS discussed here, are commonly taken from batches of Nuclear forensics is an emerging science, U oxide product for analysis and archive. driven primarily by national security objectives, Determining the type of reactor in which the including those of both law enforcement and HEU was irradiated is a much more involved national intelligence. Nuclear forensics is one input process, using knowledge of reactor designs and into nuclear attribution, in which responsibility is operating conditions and computer modeling of fuel assigned, along with other sources of information, burn-up. Calculations were performed with the such as law enforcement and intelligence. Nuclear ORIGEN2 code to determine the initial isotope forensics is used to generate technical conclusions abundances and the reactor neutron spectrum most by applying validated signatures to analytical results consistent with the observed U isotope abundances. from the interdicted material. These validated These calculations indicate that a thermal energy signatures include both comparative signatures, in spectrum and a burn-up exposure of ~350,000 which the interdicted material is compared to the MWD/MT best match the measured U isotope results from material of known origins, and abundances. The most likely source is a light water predictive signatures, in which conclusions are

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generated without reference to other samples. Valid BRENNECKA, G.A., BORG, L.E., HUTCHEON, I.D., analytical results, in turn, depend on appropriately SHARP, M.A. AND ANBAR, A.D. (2010): Natural validated analytical methods, proper analytical variations in uranium isotope ratios of uranium sampling, and a quality control/assurance program. ore concentrates: understanding the U-238/U-235 fractionation mechanism, Earth Planet. Sci. Lett. ACKNOWLEDGEMENTS 291, 228-235. We thank the members of the LLNL nuclear COMMUNIQUÉ 2012 SEOUL NUCLEAR SECURITY forensics team for their many contributions and SUMMIT (2012) http://www.thenuclearsecurity stimulating engagement and who deserve full credit summit.org/userfiles/Seoul%20Communique_FIN for the activities described herein. We also thank A. AL.pdf Simonetti for a thorough review and helpful DOLGOV, J., BIBILASHVILI, Y.K., CHOROKHOV, comments. This chapter was prepared by a N.A., SCHUBERT, A, JANSSEN, G., MAYER, K. & contractor of the U.S. Government under contract KOCH, L. (1999): Installation of a database for number DE-AC52-07NA27344. Accordingly, the identification of nuclear material of unknown U.S. Government retains a nonexclusive, royalty- origin, Proc. 21st ESARDA Symposium, free license to publish or reproduce the published VNIINM Moscow, 1999, Sevilla, Spain, Report form of this contribution, or allow other to do so, for EUR 18963 EN. U.S. Government purposes. DREICER, M., HUTCHEON, I.D., KRISTO, M.K., REFERENCES SMITH, D.K., VERGINO, E.S. & WILLIAMS, R.W. (2009): International Nuclear Forensics Cooper- ADAMSON, M., ALCARAZ, A., ANDRESEN, B., ation – Future Opportunities, Proceedings of the BAZAN, J., CANTLIN, S., CHAMBERS, D., 50th Institute for Nuclear Materials Management CONRADO, C., ESSER, B., GRANT, P., HUDSON, B., (INMM) Meeting, Tucson, AZ. HUTCHEON, I., MENAPACE, J., MOODY, K., MORAN, J., NIEMEYER, S., OVERTURF, G., FEDCHENKO V. (2007): Weapons of Mass Analysis, RANDICH, E., ROBBINS, W., RUSS, P., WALL, M., Jane’s Intelligence Review 19, No. 11, pp. 48-51. WHIPPLE, R., WILLIAMS, R., ZELLAR, L., FEDCHENKO V. (2008): Nuclear Forensic Analysis, PERSIANI, P., BICHA, W., BOLINGER, W., CARTER, SIPRI Yearbook 2008: Armaments, Disarma- J., CHAMBERS, C., GOODPASTURE, T., HEMBREE ment, and International Security (Oxford JR., D., HINTON JR., E., RAYBORN, C., THOMPSON, University Press), pp. 415-427. K., TUCKER, H., WILSON, J., FINCH, D., GOUGE, GASCOYNE, M. (1992): Geochemistry of the T., HALVERSON, J., WALTER S., WEBB, R., RAY, I. Actinides and Their Daughters. In: Uranium & STREZOV, A. (2001): Forensic Analysis of a Series Disequilibrium: Applications to Earth, Smuggled HEU Sample Interdicted in Bulgaria. Marine, and Environmental Sciences (M. UCRL-ID-143216. Lawrence Livermore National Ivanovich & R.S. Harmon, eds.) 2nd Ed., Laboratory, U.S. Department of Energy, Clarendon Press, Oxford. Livermore, CA, pp. 88. GLOBAL SECURITY NEWSWIRE (2010): Men admit to AREVALO, R., JR., BELLUCCI, J., & MCDONOUGH, attempting HEU sale in Georgia, http://www.nti. W. F. (2010): Geostand. & Geoanalyt. Res. 34, org/gsn/article/men-admit-to-attempting-heu-sale- 327-341 DOI: 10.1111/j.1751-908X.2010. in-georgia/ 00934.x GLOBAL SECURITY NEWSWIRE (2011): Moldova, BAUDE S. (2008): HEU seized in July 2001 in Paris: U.S. Pursue HEU Held by Criminal Organization, Analytical investigations performed on the http://www.nti.org/gsn/article/moldova-us- material. Proc. IAEA Conference on Illicit pursue-heu-held-by-criminal-organization/ Nuclear Trafficking, Edinburgh, Scotland, 19–22 GRANT, P.M., MOODY, K.J., HUTCHEON, I.D., November 2007 pp. 397–399. PHINNEY, D.L., WHIPPLE, R.E., HAAS, J.S., BAUDE, S., CHARTIER, B., KIMMEL, D., MARIOTTE, ALCARAZ, A, ANDREWS, J.E., KLUNDER, G.L., F., MASSE, D., PERON, H., TILLY, D. (2008): The RUSSO, R.E., FICKIES, T.E., PELKEY, G.E., French response in cases of illicit nuclear ANDRESEN, B.D., KRUCHTEN, D.A. & CANTLIN, trafficking. Proc. IAEA Conference on Illicit S. (1998): Nuclear forensics in law enforcement Nuclear Trafficking, Edinburgh, Scotland, 19-22 applications, J. Radioanal. Nucl. Chem., 235(1- November 2007 pp. 363-372. 2), 129.

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