Nuclear forensics methodology identifies legacy plutonium from the Manhattan Project

Discerning Transuranic Sub-Concealments in Nuclear Waste Barrels Using γ-Ray Spectrometry: A Non-Invasive Assay Strategy To Combat the Threat of Nuclear Diversion

Insufficient inventory control arising from inadequate monitoring procedures can lead to vulnerabilities in nuclear security. In addition, insider threats, by either malicious intent or negligence, can pose a substantial risk by exploiting such deficiencies to perform unlawful actions, such as theft or diversion, which may lead to compromised nuclear security. Interim storage barrels, intended for temporary containment of low-density nuclear waste, require special attention in this regard. In certain scenarios, the inadequacy of the existing waste barrel assay methodologies to identify and correctly measure any undesirable transuranic subconcealment present inside may pose a risk of nuclear diversion. The present work aims to establish an absolute waste barrel assay procedure to mitigate such risks by offering a robust method for the detection and assay of transuranic subconcealments in nuclear waste barrels using high-resolution γ-ray spectrometry. Challenges related to the varying amounts of attenuation experienced by the γ-rays within the subconcealments, low-density matrix, and the steel barrel wall have been addressed by an iterative photopeak efficiency transfer approach. The methodology has been verified for the assay of seven mock-up samples mimicking nuclear diversion attempts using waste barrels, for which conventional barrel scanning would be inadequate and tomographic scanning would be highly time-consuming. Using this methodology, Pu and 241Am isotopes have been assayed within <10% of the expected value for the majority, with the measurement uncertainty of <10%. The present method, which is simple and noninvasive, can identify inconsistencies with the labeled inventory and detect potential diversion attempts.

Interrogating a Mixed Actinide Basket Using High-Resolution γ-Ray Spectrometry: A Nuclear Forensic Perspective on Possible Smuggling Scenarios

The total fissile content in seized nuclear materials is of immense importance and needs to be estimated with reasonable accuracy as a part of nuclear forensics for early decision-making in legal proceedings. High-resolution γ-ray spectrometry (HRGRS), because of its nondestructive nature, is a powerful tool for the assay of such samples to reach a quick "on-site" decision on the severity, intended use, and associated radiological threat. If the seized package contains fissile isotopes of more than one actinide in a multicompartmental heterogeneous mixture, analogous to the most likely scenario of a "smuggled mixed actinide basket", its "on-site" quantification can be extremely challenging. This makes up an increasing share of the absolute HRGRS in nuclear forensics and demands for fundamentally new approaches. In the present work, the challenges associated with varying attenuation experienced by γ-rays of different actinides at different subcontainments of the heterogeneous sample matrix have been addressed by an iterative efficiency transfer approach from "point" to "extended" source for individual actinides and demonstrated for the assay of four mock-up samples and a legacy packet, mimicking seized packages containing nuclear materials. An absolute isotopic inventory of the fissile and other radioisotopes has been obtained within <10% along with the assay of total U and Pu within <3% of the expected values with measurement uncertainty <10% for the majority. The present approach has a good potential for "on-site" nuclear forensics in nuclear smuggling scenarios and also can be adapted easily for a wide variety of other applications.

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.

3D printed field-deployable microfluidic systems for the separation and assay of Pu in nuclear forensics

A compact field-deployable microfluidic system has been developed to improve timelines for the rapid analysis of debris in post-detonation nuclear forensics. We used a high-resolution 3D printer to miniaturize typical laboratory-based procedures into a fieldable platform. Microfluidic half-modules were produced for the purification of Pu from excess U, along with a portable alpha chamber for the following isotopic analysis of the Pu stream. A porous PTFE membrane is soaked with a hydrophobic tributyl phosphate (TBP) solution and is placed between two half-modules; separation is performed as a liquid-liquid extraction in an extraction channel across this membrane, where the forward and back-extractions occur within one complete module. Following separation, a 100 μL sampling of the Pu-bearing stream is injected into a small-footprint 3D printed alpha chamber for isotopic assay via alpha spectrometry as part of an online process. In this first demonstration of microfluidic separation coupled with online alpha spectrometry, high extraction yields have been obtained for Pu (98.9 ± 4.0)% and U (97.5 ± 2.5)%. The process uses less than 800 μL of solution with separation chemistry complete within 45 minutes and subsequent alpha spectrometry initiating 25 minutes after separation.