Gamma/neutron time-correlation for special nuclear material characterization %3CU%2B2013%3E active stimulation of highly enriched uranium.

Marleau, Peter; Nowack, Aaron B.; Clarke, Shaun D.; Monterial, Mateusz; Paff, Marc; Pozzi, Sara A.

doi:10.2172/1096490

Cited by 4 publications

(3 citation statements)

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“…The TCPH technique has also been employed in conjunction with active measurements of highly enriched uranium (HEU) in bare and reflected configurations [27,40]. These measurements and corresponding simulations used a variety of neutron sources to interrogate HEU shells to estimate their neutron multiplication.…”

Section: Time-correlated Pulse-height Analysismentioning

confidence: 99%

Exploiting fission chain reaction dynamics to image fissile materials

Chapman

Mueller

Newby

et al. 2019

Nuclear Instruments and Methods in Physics Research Section A:

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Radiation imaging is one potential method to verify nuclear weapons dismantlement. The neutron coded aperture imager (NCAI), jointly developed by Oak Ridge National Laboratory (ORNL) and Sandia National Laboratories (SNL), is capable of imaging sources of fast (e.g., fission spectrum) neutrons using an array of organic scintillators. This work presents a method developed to discriminate between non-multiplying (i.e., non-fissile) neutron sources and multiplying (i.e., fissile) neutron sources using the NCAI. This method exploits the dynamics of fission chain-reactions; it applies time-correlated pulse-height (TCPH) analysis to identify neutrons in fission chain reactions.TCPH analyzes the neutron energy deposited in the organic scintillator vs. the apparent neutron time-of-flight. Energy deposition is estimated from light output, and time-of-flight is estimated from the time between the neutron interaction and the immediately preceding gamma interaction.Neutrons that deposit more energy than can be accounted for by their apparent time-of-flight are identified as fission chain-reaction neutrons, and the image is reconstructed using only these neutron detection events. This analysis was applied to measurements of weapons-grade plutonium (WGPu) metal and 252 Cf performed at the Nevada National Security Site (NNSS) Device Assembly Facility (DAF) in July 2015. The results demonstrate it is possible to eliminate the non-fissile 252 Cf source from the image while preserving the fissile WGPu source. TCPH analysis was also applied to additional scenes in which the WGPu and 252 Cf sources were measured individually. The results of these separate measurements further demonstrate the ability to remove the non-fissile 252 Cf source and retain the fissile WGPu source. Simulations performed using MCNPX-PoliMi indicate that in a one hour measurement, solid spheres of WGPu are retained at a 1σ level for neutron multiplications M 3.0 and above, while hollow WGPu spheres are retained for M 2.7 and above.

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Section: Time-correlated Pulse-height Analysismentioning

confidence: 99%

Exploiting fission chain reaction dynamics to image fissile materials

Chapman

Mueller

Newby

et al. 2019

Nuclear Instruments and Methods in Physics Research Section A:

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“…For the past several years, Sandia National Laboratories and the University of Michigan have been collaborating on a new technique that uses both the timing between correlated gamma rays and neutrons in conjunction with the energy deposited by correlated neutrons. These signatures were first combined into Time-Correlated Pulse Height (TCPH) distributions which were shown to be sensitive to multiplication of neutrons within fissile material and by extension the material mass and presence of intervening moderators or reflectors [13,14,15,16,17]. The TCPH distribution is a raw representation of the measured signature in a bi-variate histogram of the neutron deposited energy and the time to correlated gamma ray.…”

Section: Time Of Flight Fixed By Energy Estimationmentioning

confidence: 99%

Characterizing subcritical assemblies with time of flight fixed by energy estimation distributions

Monterial¹,

Marleau²,

Pozzi³

2018

Nuclear Instruments and Methods in Physics Research Section A:

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We present the Time of Flight Fixed by Energy Estimation (TOFFEE) as a measure of the fission chain dynamics in subcritical assemblies. TOFFEE is the time between correlated gamma rays and neutrons, subtracted by the estimated travel time of the incident neutron from its proton recoil. The measured subcritical assembly was the BeRP ball, a 4.482 kg sphere of α-phase weapons grade plutonium metal, which came in five configurations: bare, 0.5, 1, and 1.5 in iron, and 1 in nickel closed fitting shell reflectors. We extend the measurement with MCNPX-PoliMi simulations of shells ranging up to 6 inches in thickness, and two new reflector materials: aluminum and tungsten. We also simulated the BeRP ball with different masses ranging from 1 to 8 kg. A two-region and single-region point kinetics models were used to model the behavior of the positive side of the TOFFEE distribution from 0 to 100 ns. The single region model of the bare cases gave positive linear correlations between estimated and expected neutron decay constants and leakage multiplications. The two-region model provided a way to estimate neutron multiplication for the reflected cases, which correlated positively with expected multiplication, but the nature of the correlation (sub or super linear) changed between material types. Finally, we found that the areal density of the reflector shells had a linear correlation with the integral of the two-region model fit. Therefore, we expect that with knowledge of reflector composition, one could determine the shell thickness, or vice versa. Furthermore, up to a certain amount and thickness of the reflector, the two-region model provides a way of distinguishing bare and reflected plutonium assemblies.Research and development is generally geared towards accounting for the differences in thermal capture He-3based systems and FNMCs [9]. As a result, the development of new measurement systems is underpinned by more or less the same multiplicity analysis developed over three decades ago. Therefore, data analysis using new measurement systems continue to require both high efficiency and accurate knowledge of the efficiency of the system. This creates A design principle that drives systems toward larger sizes and geometries that limit applications and portability. However, portability is often a feature demanded by field applications such as treaty verification and nuclear emergency response.Instead of optimizing fast organic scintillator-based systems to the design principles of multiplicity counting, we have leveraged a few key additional signatures available to these detectors while investigating new analysis methodologies:1. Prompt gamma rays released from fission, which are distinguished from neutrons with pulse shape discrimination (PSD) [10] [11] 2. Energy imparted by incident neutrons measured through proton recoil. 3. Timing between these detected events, measured with arXiv:1801.08126v1 [physics.data-an]

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“…The utility of the TCPH distribution has been extensively studied with non-multiplying 252 Cf [5], low-multiplying mixed oxide powder and plutonium-gallium disks [6], and highly enriched uranium [7] measurements and simulations [8]. BeRP ball experiments measuring the TCPH as a signature have only thus far been simulated, and these results demonstrated a correlation between multiplication and spreading in the TCPH distribution [9].…”

Section: Motivation and The New Approachmentioning

confidence: 99%

Multiplication and Presence of Shielding Material from Time-Correlated Pulse-Height Measurements of Subcritical Plutonium Assemblies

Monterial

Marleau

Paff

et al. 2017

Nuclear Instruments and Methods in Physics Research Section A:

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We present the results from the first measurements of the Time-Correlated Pulse-Height (TCPH) distributions from 4.5 kg sphere of α-phase weapons-grade plutonium metal in five configurations: bare, reflected by 1.27 cm and 2.54 cm of tungsten, and 2.54 cm and 7.62 cm of polyethylene. A new method for characterizing source multiplication and shielding configuration is also demonstrated. The method relies on solving for the underlying fission chain timing distribution that drives the spreading of the measured TCPH distribution. We found that a gamma distribution fits the fission chain timing distribution well and that the fit parameters correlate with both multiplication (rate parameter) and shielding material types (shape parameter). The source-to-detector distance was another free parameter that we were able to optimize, and proved to be the most well constrained parameter. MCNPX-PoliMi simulations were used to complement the measurements and help illustrate trends in these parameters and their relation to multiplication and the amount and type of material coupled to the subcritical assembly.

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Gamma/neutron time-correlation for special nuclear material characterization %3CU%2B2013%3E active stimulation of highly enriched uranium.

Cited by 4 publications

References 1 publication

Exploiting fission chain reaction dynamics to image fissile materials

Exploiting fission chain reaction dynamics to image fissile materials

Characterizing subcritical assemblies with time of flight fixed by energy estimation distributions

Multiplication and Presence of Shielding Material from Time-Correlated Pulse-Height Measurements of Subcritical Plutonium Assemblies

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