Safeguards Applications Research Articles

Rapid paper spray mass spectrometry characterization of uranium and exemplar molecular species

The ability to detect and quantify the presence of specific inorganic elements and complexes is essential for environmental monitoring and nuclear safeguards applications. In this work, paper spray ionization mass spectrometry was used for the rapid chemical and isotopic characterization of trace inorganic species collected on cotton swipe substrates. The direct analysis of cotton swipes using this ambient ionization technique led to fast sample analysis that retained original chemical information of the source material with minimal sample preparation. Mass spectra were collected with an atmospheric pressure ionization, high-resolution mass spectrometer for solutions containing uranyl acetate, uranyl chloride, uranyl nitrate, and uranyl tri-n-butylphosphate complexes. Gadolinium nitrate was used as an internal standard for the quantitative analysis of uranium. To demonstrate the ability to characterize inorganic contaminants in the presence of uranium, a multi-element inorganic standard containing U, Bi, Pb, Cd, Fe, and Zn was deposited onto cotton substrates and directly analyzed without purification. All elements doped on the cotton substrate were detected with strong signal-to-noise ratios (ca 1000 for UO2 + on multi-element doped swipes) and high integrated intensities (>105 counts) from collection periods of approximately 1 min. Limits of detection were determined to be approximately 94 ng for UO2 + and uranyl acetate through the measurement of ppb level solutions. The rapid analysis of uranium and other inorganic-containing samples while still retaining original chemical information (e.g. uranyl complexation) was demonstrated. Qualitative detection and speciation were achieved in less than 1 min of analysis. For uranium isotopic quantitation, longer accumulations (>15 min) can be sustained to improve the accuracy of minor 235 U isotopic abundance measurements to approximately 1% error.

Suggested Modification of the Fundamental Parameter Method: A Case Study to Calculate the Optimum Absolute Intensity of 1001.03 keV Gamma-Ray Transition-

Abstract. The fundamental parameter method (FPM) is an analytical approach for intrinsic calibration of gamma-ray spectrometer using fundamental nuclear and atomic parameters such as gamma-ray branching intensity, half-life time, isotopic ratio and concentration ratio. The main advantage of this approach is the wide range of its applications in gamma-ray efficiency calibration, nuclear safeguards (nuclear materials measurement and isotopic ratios) and others. In this work, the calculation of relative efficiency (RE; photopeak count rate divided by branching ratio) was modified based on the relative intensity concept of 226Ra in equilibrium with 222Rn decay products (214Bi-214Pb). The modified FPM was applied to reevaluate the absolute intensity (I%) of gamma-ray transition of 234mPa at 1001.03 keV. using certified uranium ore samples, 226Ra point source and gamma-ray spectrometers based on hyper pure germanium detector. The newly confirmed I % of 1001.03 keV is 1.0164±0.0636. Key words: fundamental parameter method/ 1001.03 keV/ gamma-ray transition/ 238U

Fast neutron- and [formula omitted]-ray coincidence detection for nuclear security and safeguards applications

The use of passive and active interrogation techniques to evaluate materials concerning their content of special nuclear materials (SNM) is fundamental in fields such as nuclear safeguards and security. Detection of fast neutrons and γ rays, which are a characteristic signature of SNM, has several potential advantages compared with the commonly used systems based on thermal and epithermal neutron counters, the most important being the much shorter required coincidence times and the correspondingly reduced rate of background events due to accidental coincidences. Organic scintillators are well suited for this purpose due to their fast timing properties and composition being based on carbon and hydrogen with large elastic scattering cross-sections for fast neutrons. Organic scintillators also have suitable detection efficiency for γ rays and exhibit pulse shape properties which are favorable for distinguishing between neutrons and γ rays. This paper presents experimental results and Monte Carlo simulations for a neutron–neutron and γ-neutron coincidence detection setup for identification and characterization of SNM based on such detectors. The measurements were carried out on different samples of PuO2 material with varying content of 240Pu at the Joint Research Center (JRC) of the European Commission, Ispra, Italy. The results demonstrate significant advantages of fast neutron-γ coincidence detection over fast neutron–neutron coincidence counting for certain applications, e.g. for nuclear security systems, even in the presence of moderate amounts of shielding.

Antitrust Overreach: Undoing Cooperative Standardization in the Digital Economy

Information technology markets in general and wireless communications markets, in particular, rely on standardization mechanisms to develop interoperable devices for data processing, storage, and transmission. From 2G through the emergent 5G standard, wireless communications markets have largely achieved standardization through cooperative multi-firm arrangements that likely outperform the historically dominant alternatives of government monopoly, which is subject to informational deficits and regulatory capture, and private monopoly, which suffers from pricing and other distortions inherent to protected market positions. This cooperative process has successfully relied on three key legal elements: reasonably secure patents, quasi-contractual licensing commitments supplemented by reputation effects, and targeted application of antitrust safeguards against collusion risk. Over approximately the past decade, antitrust agencies and courts in the U.S., Europe and Asia have taken actions that threaten this legal infrastructure by limiting patentees’ ability to seek injunctive relief, adopting rigid understandings of “fair, reasonable and non-discriminatory” licensing principles, and addressing collusion risk among licensors-innovators while overlooking (and even exacerbating) collusion risk among licensees-implementers. These judicial and regulatory interventions in IP licensing markets shift value from firms and economies that specialize in generating innovations to firms and economies that specialize in integrating innovations into end-user products. These entity-level and country-level redistributive effects are illustrated by lobbying activities in the wireless communications markets and antitrust actions against IP licensors in jurisdictions that have substantial net IP deficits and are principally populated by IP licensees. Current antitrust policy promotes producers’ narrow interests in lower input costs while ignoring the broader public interest in preserving the cooperative standardization structures that have supported innovation and commercialization in the digital economy.

Governing the Water-Energy-Food Nexus Related to Hydropower on Shared Rivers—The Role of Regional Organizations

An evolving literature on the Water-Energy-Food (WEF) nexus argues that there is a need to better understand the conditions under which nexus coordination may occur. A case in point are hydropower investments on shared rivers which might impact the provision of energy, water and food security across borders. In international basins, governing the WEF nexus impacts of hydropower relies on voluntary negotiations between the respective countries involved. It has been argued that such negotiations may be facilitated by regional organizations, such as international river basin organizations (IRBOs), but this claim has hardly been investigated systematically. Drawing on regime theory in international relations and the literature on benefit sharing, this paper asks what role regional organizations may play in governing hydropower-related WEF nexus impacts. It compares three cases of hydropower planning on shared rivers. The Rusumo Falls and the Ruzizi III hydropower projects (HPPs) are joint investments in Africa's Great Lakes region facilitated by an IRBO and a regional energy organization, respectively. On the Mekong, Laos is constructing the Xayaburi dam despite reservations by the Mekong River Commission and downstream riparians. The paper finds IRBOs and regional energy organizations may play a role in facilitating cross-border nexus governance by supporting benefit-sharing arrangements and by fostering the application of environmental and social safeguards and international law principles. However, it also shows that the influence of regional organizations varies, and how successfully they support nexus governance also depends on whether the HPP is planned unilaterally or jointly; the availability and consensus on data on nexus impacts; and the presence or absence of donors and private sector capital and investors.

Novel muon imaging techniques.

Owing to the high penetrating power of high-energy cosmic ray muons, muon imaging techniques can be used to image large bulky objects, especially objects with heavy shielding. Muon imaging systems work just like CT scanners in the medical imaging field-that is, they can reveal information inside of a target. There are two forms of muon imaging techniques: muon absorption imaging and muon multiple scattering imaging. The former is based on the flux attenuation of muons, and the latter is based on the multiple scattering of muons in matter. The muon absorption imaging technique is capable of imaging very large objects such as volcanoes and large buildings, and also smaller objects like spent fuel casks; the muon multiple scattering imaging technique is best suited to inspect smaller objects such as nuclear waste containers. Muon imaging techniques can be applied in a broad variety of fields, i.e. from measuring the magma thickness of volcanoes to searching for secret cavities in pyramids, and from monitoring the borders of countries checking for special nuclear materials to monitoring the spent fuel casks for nuclear safeguards applications. In this paper, the principles of muon imaging are reviewed. Image reconstruction algorithms such as Filtered Back Projection and Maximum Likelihood Expectation Maximization are discussed. The capability of muon imaging techniques is demonstrated through a Geant4 simulation study for imaging a nuclear spent fuel cask.This article is part of the Theo Murphy meeting issue 'Cosmic-ray muography'.

Determination of the uranium enrichment without calibration standards using a 2 × 2 inch LaBr3(Ce) room temperature detector and Monte Carlo sampling approach for uncertainty assessment

In recent years room temperature medium resolution scintillation devices, such as LaBr3(Ce), have attracted much interest as possible alternatives to traditional spectrometers based on HPGe and NaI detectors, for the determination of the uranium enrichment in safeguards applications. This paper focuses on the investigation of possibilities and limits of a net peak area based methodology used for the determination of the uranium enrichment without use of calibration standards and introduces the isotopic code MCSIGMA for LaBr3(Ce) scintillators. Tests are conducted with a room temperature, medium resolution spectrometer based on a 2×2 inch LaBr3(Ce) scintillator using which spectra of different statistical quality are obtained from certified uranium standards. Gamma peaks in the 143-1001keV energy range are used as uranium gamma-ray signatures. Results indicate a promising performance of the applied methodology with a room temperature medium resolution scintillator of the LaBr3(Ce) type, however at a cost of significantly higher uncertainty budget on the derived enrichment compared to HPGe, especially for natural and depleted uranium samples. This uncertainty budget is primarily influenced by the statistical quality of the measured spectra. Implemented algorithms and analysis routines are described in detail and presented.

Antitrust Overreach: Undoing Cooperative Standardization in the Digital Economy

Information technology markets in general, and wireless communications markets in particular, rely on standardization mechanisms to develop interoperable devices for rapid and secure data processing, storage and transmission. From 2G through the emergent 5G standard, wireless communications markets have largely achieved standardization through cooperative multi-firm arrangements that likely outperform the historically dominant alternatives of government monopoly, which is subject to informational deficits and regulatory capture, and private monopoly, which suffers from pricing and other distortions inherent to protected market positions. This cooperative process has successfully relied on a mix of reasonably secure patents, quasi-contractual licensing commitments supplemented by reputational discipline, and targeted application of antitrust safeguards against collusion risk. Over approximately the past decade, antitrust agencies and courts have taken actions that threaten this legal infrastructure by limiting patentees’ ability to seek injunctive relief, adopting rigid understandings of the “fair, reasonable and non-discriminatory” licensing commitment, and focusing on collusion risk among licensors-innovators while overlooking (and even exacerbating) collusion risk among licensees-implementers. This incremental erosion of IP and contractual security shifts value from firms and economies that specialize in generating technology inputs to firms and economies that specialize in integrating technology inputs into consumption goods. These entity-level and country-level redistributive effects are illustrated by the origins of the “FRAND” requirement at the onset of the European cellular telephone market and antitrust enforcement actions against IP licensors in jurisdictions that have substantial net IP deficits and are principally populated by firms that operate in the downstream stages of the technology supply chain. The current policy trajectory promotes producers’ and assemblers’ narrow interests in lower input costs while ignoring the broader public interest in preserving the cooperative standardization structures that have supported innovation and commercialization in wireless communications markets.

La aplicación de la Canasta Comercial Transfronteriza como medida de reactivación comercial en Carchi – Ecuador. Un análisis de proyecciones con tendencia polinómica

La devaluación del peso colombiano frente al dólar, la aplicación de salvaguardas por parte del Gobierno ecuatoriano, la baja del precio del petróleo a nivel mundial, entre otros factores, deprimió el comercio fronterizo en Ecuador, esencialmente en la provincia del Carchi donde el principal ingreso económico es por actividades comerciales con el departamento de Nariño, al sur de Colombia. Una de las medidas que adoptó el Gobierno de Rafael Correa fue la de declarar a la Provincia del Carchi como “zona deprimida” el 18 de agosto de 2015, y cuyo objetivo era que los comerciantes registrados en el Servicio de Rentas Internas SRI, puedan adquirir productos en Colombia para venderlos en su localidad a precios competitivos generando reactivación comercial. Esta investigación utiliza el método analítico y sistémico, con un enfoque técnico aplicado en dos casos de empresas del sector comercial, utilizando proyecciones con tendencia polinómica para alcanzar conclusiones diagnósticas.

Light propagation in a neutron detector based on 6Li glass scintillator particles in an organic matrix

Composite materials consisting of 6Li scintillator particles in an organic matrix can enable thermal neutron detectors with excellent rejection of gamma-ray backgrounds. The efficiency of transporting scintillation light through such a composite is critical to the detector performance. This optical raytracing study of a composite thermal neutron detector quantifies the various sources of scintillation light loss and identifies favorable photomultiplier tube (PMT) readout schemes. The composite material consisted of scintillator cubes within an organic matrix shaped as a right cylinder. The cylinder surface was surrounded by an optical reflector, and the light was detected by PMTs attached to the cylinder end faces. A reflector in direct contact with the composite caused 53% loss of scintillation light. This loss was reduced 8-fold by creating an air gap between the composite and the reflector to allow a fraction of the scintillation light to propagate by total internal reflection. Replacing a liquid mineral oil matrix with a solid acrylic matrix decreased the light transport efficiency by only ∼10% for the benefit of creating an all-solid-state device. The light propagation loss was found to scale exponentially with the distance between the scintillation event and the PMT along the cylinder main axis. This enabled a PMT readout scheme that corrects for light propagation loss on an event-by-event basis and achieved a 4.0% energy resolution that approached Poisson-limited performance. These results demonstrate that composite materials can enable practical thermal neutron detectors for a wide range of nuclear non-proliferation and safeguard applications.

Multi-layer fast neutron detectors based on composite heavy-oxide scintillators for detection of illegal nuclear materials

We developed and characterized a new type (designated ZEBRA) of multi-layer composite heavy-oxide scintillatordetectors for fast neutron detection for homeland security and nuclear safeguards applications. In this heterogeneous detector medium, composite layers comprised of micro-granules of heavy-oxide scintillators (ZWO, CWO, PWO, BGO, GSO(Ce), GOS(Ce) and others) dispersed in transparent plastic are alternated with layers of clear plastic that serve as scintillation light guides and as a neutron moderator material. The physical peculiarities of the neutron interactions and the principal mechanisms of fast neutron registration in these detectors are discussed in detail. The fast neutron intrinsic detection efficiencies and sensitivities of ZEBRA-detectors based on BGO, ZWO and GSO(Ce) composite scintillators in response to neutrons from 239Pu–Be and 252Cf sources were measured. These detectors had cross-sectional areas ranging from 16 to 100 cm2. The sensitivities of such detectors of size 100×100×41 mm3 were found to be 40–51 cps/(nps × cm−2), a level that is comparable to the sensitivity of a typical 3He counter of 1600 cm2 area. The intrinsic efficiencies and sensitivities of the ZEBRA-detectors also compare favorably with those of fast neutron detectors based on large-size heavy-oxide single crystals, but the multi-layer composite ZEBRA structures are much less expensive and can be easily manufactured in much larger dimensions. This work represents a significant advance from earlier single-crystal detector types as part of our effort to explore alternatives and improvements to conventional 3He counters.

Demonstration of gamma-ray pipe-monitoring capabilities for real-time process monitoring safeguards applications in reprocessing facilities

ABSTRACT Nuclear material in reprocessing facilities is safeguarded by random sample verification with additional process monitoring applied to solution masses and volumes within the tanks to maintain continuity-of-knowledge of the operational processes. Measuring the unique gamma rays of each solution as the material flows through pipes connecting all tanks and process apparatuses could potentially improve process monitoring by verifying the composition in real time. We tested this gamma-ray pipe-monitoring method using plutonium-nitrate solution transferred between tanks at the Plutonium Conversion Development Facility at the Tokai Reprocessing Plant of the Japan Atomic Energy Agency. The gamma rays were measured with a lanthanum-bromide detector and a list-mode data acquisition system to obtain both time and energy information to evaluate the solution nuclear material as well as process conditions. Developed offline, we demonstrate this method can determine isotopic composition, flow-rate, volume, and process timing of a solution batch, introducing a viable online, in-line, unattended capability for improved process monitoring safeguards verification. The process and measurement details are presented here along with a description of the analyses used and the results of the evaluation.

Minor isotope safeguards techniques (MIST): Analysis and visualization of gas centrifuge enrichment plant process data using the MSTAR model

This paper presents a development related to the use of minor isotope safeguards techniques (MIST) and the MSTAR cascade model as it relates to the application of international nuclear safeguards at gas centrifuge enrichment plants (GCEPs). The product of this paper is a derivation of the universal and dimensionless MSTAR cascade model. The new model can be used to calculate the minor uranium isotope concentrations in GCEP product and tails streams or to analyze, visualize, and interpret GCEP process data as part of MIST. Applications of the new model include the detection of undeclared feed and withdrawal streams at GCEPs when used in conjunction with UF6 sampling and/or other isotopic measurement techniques.

Instrumentation effects on U and Pu CBNM standards spectra quality measured on a 500 mm3CdZnTe and a 2×2 inch LaBr3detectors

Nowadays, there is interest in developing gamma-ray measuring devices based on the room temperature operated medium resolution detectors such as semiconductor detectors of the CdZnTe type and scintillators of the LaBr3type. This is true also for safeguards applications and the International Atomic Energy Agency (IAEA) has launched a project devoted to the assessment of medium resolution gamma-ray spectroscopy for the verification of the isotopic composition of U and Pu bearing samples. This project is carried out within the Non-Destructive Assay Working Group of the European Safeguards Research and Development Association (ESARDA). In this study we analyze medium resolution spectra of U and Pu standards with the aim to develop an isotopic composition determination algorithm, particularly suited for these types of detectors. We show how the peak shape of a CdZnTe detector is influenced by the instrumentation parameters. The experimental setup consisted of a 500 mm3CdZnTe detector, a 2×2 inch LaBr3detector, two types of measurement instrumentation – an analogue one and a digital one, and a set of certified samples – a207Bi point source and U and Pu CBNM standards. The results of our measurements indicate that the lowest contribution to the peak asymmetry and thus the smallest impact on the resolution of the 500 mm3 CdZnTe detector was achieved with the digital MCA. Analysis of acquired spectra allowed to reject poor quality measurement runs and produce summed spectra files with the least impact of instrumentation instabilities. This work is preliminary to further studies concerning the development of an isotopic composition determination algorithm particularly suited for CZT and LaBr3 detectors for safeguards applications.

Costs of delivery approaches for providing livelihood projects to local communities as part of REDD+ programmes: An analysis from Madagascar

SUMMARYProviding benefits to local people from forest conservation programmes is an important issue for policy makers. Livelihood projects are a common way to provide benefits, but there is little information about their costs. We analysed 463 livelihood projects in the Ankeniheny-Zahamena Corridor Reducing Emissions from Deforestation and Degradation (REDD+) pilot project in Madagascar to understand how different approaches to delivering livelihood projects affect costs. We compared costs across four approaches: conservation agreements, small grants, direct implementation and application of social safeguards. The approach impacted overall costs and the proportion of funds reaching communities. Projects implemented as safeguards were most expensive and had the lowest proportion of expenditures reaching the community. Projects provided as part of conservation agreements directed the highest proportion of expenditures to communities. Our results highlight that how livelihood projects are delivered has implications for project costs and community benefits and should be an important consideration in the design and implementation of REDD+ and forest conservation policies.

High resolution gamma-ray spectroscopy at high count rates with a prototype High Purity Germanium detector

High-resolution gamma-ray spectrometers are required for applications in nuclear safeguards, emergency response, and fundamental nuclear physics. To overcome one of the shortcomings of conventional High Purity Germanium (HPGe) detectors, we have developed a prototype device capable of achieving high event throughput and high energy resolution at very high count rates. This device, the design of which we have previously reported on, features a planar HPGe crystal with a reduced-capacitance strip electrode geometry. This design is intended to provide good energy resolution at the short shaping or digital filter times that are required for high rate operation and which are enabled by the fast charge collection afforded by the planar geometry crystal. In this work, we report on the initial performance of the system at count rates up to and including two million counts per second.

Comparison of experimental results of a Quad-CZT array detector, a NaI(Tl), a LaBr3(Ce), and a HPGe for safeguards applications

A compound semiconductor detector, CdTe (or CdZnTe), has been used in various areas including nuclear safeguards applications. To address its critical drawback, low detection efficiency, which leads to a long measurement time, a Quad-CZT array-based gamma-ray spectrometer in our previous study has been developed by combining four individual CZT detectors. We have re-designed the developed Quad-CZT array system to make it more simple and compact for a hand-held gamma-ray detector. The objective of this paper aims to compare the improved Quad-CZT array system with the traditional gamma-ray spectrometers (NaI(Tl), LaBr3(Ce), HPGe); these detectors currently have been the most commonly used for verification of nuclear materials. Nuclear materials in different physical forms in a nuclear facility of Korea were measured by the Quad-CZT array system and the existing gamma-ray detectors. For measurements of UO2 pellets and powders, and fresh fuel rods, the Quad-CZT array system turned out to be superior to the NaI(Tl) and LaBr3(Ce). For measurements of UF6 cylinders with a thick wall, the Quad-CZT array system and HPGe gave similar accuracy under the same measurement time. From the results of the field tests conducted, we can conclude that the improved Quad-CZT array system would be used as an alternative to HPGes and scintillation detectors for the purpose of increasing effectivenss and efficiency of safeguards applications. This is the first paper employing a multi-element CZT array detector for measurement of nuclear materials—particularly uranium in a UF6 cylinder—in a real nuclear facility. The present work also suggests that the multi-CZT array system described in this study would be one promising method to address a serious weakness of CZT-based radiation detection.

Performance of a Boron-Coated-Straw- Based HLNCC for International Safeguards Applications

3He gas has been used in various scientific and security applications for decades, but it is now in short supply. Alternatives to 3He detectors are currently being integrated and tested in neutron coincidence counter designs, of a type which are widely used in nuclear safeguards for nuclear materials assay. A boron-coated-straw-based design, similar to the High-Level Neutron Coincidence Counter-II, was built by Proportional Technologies Inc., and has been tested by the Oak Ridge National Laboratory (ORNL) at both the JRC in Ispra and ORNL. Characterization measurements, along with nondestructive assays of various plutonium samples, have been conducted to determine the performance of this coincidence counter replacement in comparison with other similar counters. This paper presents results of these measurements.

Experimental evaluation of the extended Dytlewski-style dead time correction formalism for neutron multiplicity counting

Over the past few decades, neutron multiplicity counting has played an integral role in Special Nuclear Material (SNM) characterization pertaining to nuclear safeguards. Current neutron multiplicity analysis techniques use singles, doubles, and triples count rates because a methodology to extract and dead time correct higher order count rates (i.e. quads and pents) was not fully developed. This limitation is overcome by the recent extension of a popular dead time correction method developed by Dytlewski. This extended dead time correction algorithm, named Dytlewski–Croft–Favalli(DCF), is detailed in reference Croft and Favalli (2017), which gives an extensive explanation of the theory and implications of this new development. Dead time corrected results can then be used to assay SNM by inverting a set of extended point model equations which as well have only recently been formulated. The current paper discusses and presents the experimental evaluation of practical feasibility of the DCF dead time correction algorithm to demonstrate its performance and applicability in nuclear safeguards applications. In order to test the validity and effectiveness of the dead time correction for quads and pents, 252Cf and SNM sources were measured in high efficiency neutron multiplicity counters at the Los Alamos National Laboratory (LANL) and the count rates were extracted up to the fifth order and corrected for dead time. In order to assess the DCF dead time correction, the corrected data is compared to traditional dead time correction treatment within INCC. The DCF dead time correction is found to provide adequate dead time treatment for broad range of count rates available in practical applications.

Neutron Multiplicity Counting Moments for Fissile Mass Estimation in Scatter-Based Neutron Detection Systems

Neutron multiplicity counting (NMC) techniques are widely used for nuclear materials accountability and international safeguards applications to quantitatively evaluate characteristic properties pertaining to fissile material. Mathematical models for NMC moments have been previously derived for systems that use capture-based detectors; however, these models are not applicable when scatter-based detectors are used because of “neutron cross talk.” Neutron cross talk occurs when a single neutron scatters and deposits energy above threshold into multiple detectors causing spurious increase in multiplicity counts; this, in turn, has caused fissile mass to be overestimated when not treated. In this paper, we propose new mathematical models derived from point kinetics to correct for neutron cross-talk effects up to any arbitrary order N, where N denotes the maximum number of counts a single neutron can cause. The new models were used to estimate the fissile mass of plutonium metal and oxide samples with effective 240Pu mass ranging from 2.5 to 250 g. The adequacy of the models was confirmed using simulations of a conceptual scatter-based neutron multiplicity counter (e.g., organic scintillators) using MCNPX v2.7e with the PoliMi fission event generating extension. The fissile mass estimates with no correction for neutron cross-talk events yielded an average relative deviation from the true 240Pueff mass of 55.94% and 84.56% for metal and oxide samples, respectively. When neutron cross-talk events of order N = 2 are included in the model, the fissile mass estimates yielded an average relative deviation of 11.89% for metal and 13.21% for oxide samples. Accounting for neutron cross-talk events of order N = 3 resulted in fissile mass estimates with an average relative deviation of 9.58% and 10.51% for metal and oxide samples, respectively. These mass estimates were compared to a reference case (i.e., no neutron cross-talk effects) that yielded an average relative deviation of 6.81% and 4.77% for metal and oxide samples, respectively. The discrepancy between the estimates from the proposed model and the reference case is attributed to the assumed value of N, which sets a finite upper bound on the order of cross-talk events the model treats (i.e., the model for N = 3 assumes that a neutron will never cause more than three counts).