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

Shin, Tony H.; Hua, Michael Y.; Marcath, Matthew J.; Chichester, David L.; Pázsit, Imre; Fulvio, Angela Di; Clarke, Shaun D.; Pozzi, Sara A.

doi:10.1080/00295639.2017.1354591

Cited by 24 publications

(6 citation statements)

References 17 publications

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“…Raw Feynman-alpha analysis produced prompt periods that were greater than the reference values by a constant time offset; the uniform mean difference was 21.37 ns and the inversevariance-weighted mean difference was 20.13 ns. The time offset is due to lifetimes not associated with the multiplication kinetics such as detector dead time or neutron cross talk wherein one neutron registers multiple detections by scattering in multiple detectors [38,39].…”

Section: Resultsmentioning

confidence: 99%

On the Feynman-alpha Method for Reflected Fissile Assemblies

Hua¹,

Hutchinson²,

McKenzie³

et al. 2020

Preprint

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The Feynman-alpha method is a neutron noise technique that is used to estimate the prompt neutron period of fissile assemblies. The method and quantity are of widespread interest including in applications such as nuclear criticality safety, safeguards and nonproliferation, and stockpile stewardship; the prompt neutron period may also be used to infer the k eff multiplication factor. The Feynman-alpha method is predicated on time-correlated neutron detections that deviate from a Poisson random variable due to multiplication. Traditionally, such measurements are diagnosed with one-region point kinetics, but two-region models are required when the fissile assembly is reflected. This paper presents a derivation of the two-region point kinetics Feynman-alpha equations based on a double integration of the Rossi-alpha equations, develops novel propagation of measurement uncertainty, and validates the theory. Validation is achieved with organic scintillator measurements of weapons-grade plutonium reflected by various amounts of copper to achieve k eff values of 0.83-0.94 and prompt periods of 5-75 ns. The results demonstrate that Feynman-alpha measurements should use the two-region model instead of the one-region model. The simplified one-region model deviates from the validated two-region models by as much as 10% in the estimate of the prompt neutron period, and the two-region model reduces to the one-region model for small amounts of reflector. The Feynman-alpha estimates of the prompt neutron period are compared to those of the Rossi-alpha approach. The comparative results demonstrate that the Feynman-alpha method is more precise than the Rossi-alpha method and more accurate for k eff < 0.92, whereas the Rossi-alpha method is generally more accurate for higher multiplications. The uncertainty propagation developed in this work should be used for all Feynman-alpha measurements and will therein improve fitting accuracy and appropriate precision estimates.

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Section: Resultsmentioning

confidence: 99%

On the Feynman-alpha Method for Reflected Fissile Assemblies

Hua¹,

Hutchinson²,

McKenzie³

et al. 2020

Preprint

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“…A potential source of nonstatistical uncertainty in the OSCAR system is particle misclassification (e.g., classifying a photon as neutron) and neutron crosstalk (a single neutron rendering multiple detections, though this phenomena has been analytically addressed in Ref. [21]). A source of uncertainty for both detection systems is the chemical makeup of the RTO.…”

Section: Resultsmentioning

confidence: 99%

Simulation of the Nondestructive Assay of²³⁷Np Using Active Neutron Multiplicity Counting

Hua

Goddard

Lloyd

et al. 2019

Nuclear Science and Engineering

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The purpose of nondestructive assay in the context of nuclear safeguards is to precisely verify the declared mass of a sample of nuclear material in a noninhibitive amount of time. 237 Np is a proliferation concern, and the capacity to efficiently assay samples of it is a missing piece in the verification and safeguards toolbox. The material is subject to the same safeguards as 235 U, is reportable in gram quantities, and is classified as "other nuclear material" according to the United States Department of Energy. Given that 3000 kg of 237 Np is annually produced in the US and the bare sphere critical mass is 40-60 kg, it is desirable to augment the safeguards toolbox with a system capable of distinguishing 10 g of 237 Np in a 20-minute measurement. One measurement modality is neutron multiplicity counting, which relates the detected multiplicity count rates to the amount of fissionable material. Prior simulation work shows that an organic scintillator-based multiplicity counter can achieve the design criteria, whereas the flagship 3 He-based system, the Epithermal Neutron Multiplicity Counter, requires much longer measurement times to achieve the same precision. In this work, simultaneous measurements of a 6-kg sphere of 237 Np by organic scintillator-and 3 He-based systems are used to confirm the trends in the simulation study; the organic scintillator-based system achieves 1% uncertainty in the neutron double multiplicity rate on the order of minutes, while the 3 He-based system requires days to reach the same precision. In conclusion, the International Atomic Energy Agency should consider the development and deployment of an organic scintillator-based multiplicity counter.

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“…MCNPX-PoliMi has been used extensively in applications of nuclear fission [20,21], but never for simulating radioxenon detection. Recent work updated the code to implement the transport of conversion electrons [22], which is vital to simulating radioxenon detection because the plastic cell is used to detect these electrons.…”

Section: Mcnpx-polimi Simulationmentioning

confidence: 99%

Validation of MCNPX-PoliMi code for simulations of radioxenon beta–gamma coincidence detection

Sivels

Clarke

Padovani

et al. 2018

Nuclear Instruments and Methods in Physics Research Section A:

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Radioxenon detection is an important component of the verification regime for the Comprehensive Nuclear-Test-Ban Treaty. We developed and validated a new model in MCNPX-PoliMi to simulate the decay of various radioxenon isotopes and the detector response of a variety of detector types. The model was validated using calibration data from a plastic and NaI(Tl) beta-gamma coincidence detector and the results are presented. The results of this validation show that this model can also be used as a tool to produce training spectra and as a method to calibrate radioxenon detection systems.

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

Cited by 24 publications

References 17 publications

On the Feynman-alpha Method for Reflected Fissile Assemblies

On the Feynman-alpha Method for Reflected Fissile Assemblies

Simulation of the Nondestructive Assay of²³⁷Np Using Active Neutron Multiplicity Counting

Validation of MCNPX-PoliMi code for simulations of radioxenon beta–gamma coincidence detection

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

Cited by 24 publications

References 17 publications

On the Feynman-alpha Method for Reflected Fissile Assemblies

On the Feynman-alpha Method for Reflected Fissile Assemblies

Simulation of the Nondestructive Assay of237Np Using Active Neutron Multiplicity Counting

Validation of MCNPX-PoliMi code for simulations of radioxenon beta–gamma coincidence detection

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Simulation of the Nondestructive Assay of²³⁷Np Using Active Neutron Multiplicity Counting