CHEMICAL AND ISOTOPIC SIGNATURES FOR TRANSBOUNDARY
NUCLEAR SOURCE AND ROUTE ATTRIBUTION
David K. Smith
Lawrence Livermore National Laboratory
Livermore, California 94550 USA
The illicit trafficking of nuclear and radiological materials constitutes a significant proliferation concern around the world. Data from the International Atomic Energy Agency (IAEA) indicates 611 confirmed incidents of illicit trafficking of nuclear and radiological materials during the period January 1993 to September 2004. The IAEA defines nuclear materials as uranium, plutonium, and thorium; radioactive materials as sealed radioactive sources or bulk radioactive materials; and other materials as radioactively contaminated materials that are largely scrap. The majority of incidents involved criminal intent to steal, traffic, or illegally sell these materials.
The illegal movement of nuclear and radioactive materials is a transboundary problem. Contraband may be manufactured in one location, diverted at a second, and detected at a third. Illegal trafficking may require an appropriate law enforcement or national security response. To determine responsibility requires information on where these materials were originally manufactured, routes the material was transported, and the location where the material was diverted. Critical are diagnostic nuclear forensic signatures that allow comparison between an interdicted sample and data on origin, process, and pathways.
To accomplish these objectives a knowledge management system must provide rapid access to collect and interpret nuclear forensics signatures as part of an attribution investigation. Signature science focuses on 1) characterization of sample matrices by isotopics, trace and major elements, and physical properties including textures and morphologies 2) determination of the processes used to develop and manufacture the materials, 3) establishing the žageÓ since last irradiation or processing of the materials, 4) identifying the end-use of the materials, 5) locating the origin of the materials, and 6) inferring the point of loss-of-control. Prioritizing signatures is dependent both on the nature of the samples interdicted as well as the questions being asked of the investigation (i.e., source and/or route attribution).
A wealth of signatures may be exploited from interdicted nuclear samples. Signature collection is best phased from non-destructive characterization of ephemeral signatures to more detailed forensic analysis of robust samples. Important is the ability to raise attribution confidence by utilizing independent signatures that are mutually diagnostic (either inclusive or exclusive). The collection of signatures is a dynamic and highly deductive process. As data is acquired and analyzed, new signatures may be targeted for analysis. Forensics encompasses both nuclear and conventional (e.g., fingerprints, explosive residue, tool marks, DNA, hair, fibers, etc.) evidence; due to the nature of contaminated samples appropriate radiation safety practices must be instituted without compromising the integrity of the evidence.
The seizure of highly enriched uranium in 1999 at the Rousse, Bulgaria border checkpoint is an example of the successful application of chemical, isotopic, and morphological signatures to an investigation of illicit nuclear and radiological trafficking. Bulgarian customs officials seized a 2.4 kilogram cylindrical lead container that contained yellow paraffin wax surrounding a sealed glass ampoule filled with 4 grams of fine grained black powder. The sample was suspected to be highly enriched uranium. This evidence was returned to the United States for both nuclear and conventional forensic analysis. Electron microscopy and x-ray diffraction indicated the powder consisted of extremely fine-grained uranium oxide (U3O8). Mass spectrometry determined the sample to be highly enriched uranium (72.66 atom percent 235U and 12.13 atom percent 236U). The presence of the enriched uranium, residual plutonium, and three fission products, 125Sn, 134Cs, and 137Cs implied that the sample was derived from reprocessed, reactor-irradiated fuel. S, Cl, and Br trace element impurities in the uranium are indicative of chemical reprocessing. Analysis of the paraffin wax revealed the presence of BaCrO4 pigment rarely used in North America but prevalent elsewhere in the world. Similarly wood fibers in the paper label on the container are not indigenous North American species. Lead isotope ratios of the shipping container are also distinct from ore bodies in the United States. Nuclear and conventional forensics together identifies a pattern of illicit trafficking. Ongoing casework builds attribution confidence.
The illicit nuclear trafficking problem demands international solutions. To encourage international cooperation, the Nuclear Smuggling International Technical Working Group (ITWG) provides a common approach and effective technical solutions to governments who request assistance in nuclear forensics. The ITWG was chartered in 1996 and since that time more than 28 nations and organizations have participated in 9 international meetings and 2 analytical round-robin trials. Soon after its founding the ITWG adopted a general framework to guide nuclear forensics investigations that includes recommendations for nuclear crime scene security and analysis, the best application of radioanalytical methods, the conduct of traditional forensic analysis of contaminated materials, and effective data analysis to interpret the history of seized nuclear materials. This approach has been adopted by many nations as they respond to incidents of illicit nuclear trafficking. By encouraging the participation of those states where nuclear materials are interdicted, expertise can be brought closer to the source of these incidents. Only by sharing information about nuclear processes, materials, and signatures can participants benefit from collective experience and knowledge to evaluate and prosecute nuclear trafficking cases. Collaboration in nuclear forensics enterprise promotes international nonproliferation objectives.
This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.