Rossi-alpha measurements of fast plutonium metal assemblies using organic scintillators

Hua, Michael Y.; Bravo, C.; MacDonald, Aaron T.; Hutchinson, Jesson D.; McKenzie, George; Kiedrowski, Brian C.; Clarke, Shaun D.; Pozzi, Sara A.

doi:10.1016/j.nima.2020.163507

Cited by 15 publications

(7 citation statements)

References 22 publications

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“…Stilbene is known to exhibit highefficiency light emission properties but has poor photostability. 36,37 This stilbene derivative was then used as the organic cation for the formation of novel RInBr 4 , which is, to the best of our knowledge, one of the few known pseudoternary hybrid organic−inorganic indium(III) halides to date. The novel compound was structurally characterized using X-ray diffraction methods.…”

Section: ■ Introductionmentioning

confidence: 99%

“…In this study, an alternative approach has been taken, wherein a previously known efficient light emitter, stilbene, has been modified in a novel fashion by adding a trimethylated ammonium group to one of the two phenyl rings. Stilbene is known to exhibit high-efficiency light emission properties but has poor photostability. , This stilbene derivative was then used as the organic cation for the formation of novel RInBr 4 , which is, to the best of our knowledge, one of the few known pseudoternary hybrid organic–inorganic indium(III) halides to date. The novel compound was structurally characterized using X-ray diffraction methods.…”

Section: Introductionmentioning

confidence: 99%

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Zero-Dimensional Hybrid Organic–Inorganic Indium Bromide with Blue Emission

et al. 2021

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Low-dimensional hybrid organic–inorganic metal halides have received increased attention because of their outstanding optical and electronic properties. However, the most studied hybrid compounds contain lead and have long-term stability issues, which must be addressed for their use in practical applications. Here, we report a new zero-dimensional hybrid organic–inorganic halide, RInBr4, featuring photoemissive trimethyl(4-stilbenyl)methylammonium (R+) cations and nonemissive InBr4 – tetrahedral anions. The crystal structure of RInBr4 is composed of alternating layers of inorganic anions and organic cations along the crystallographic a axis. The resultant hybrid demonstrates bright-blue emission with Commission Internationale de l’Eclairage color coordinates of (0.19, 0.20) and a high photoluminescence quantum yield (PLQY) of 16.36% at room temperature, a 2-fold increase compared to the PLQY of 8.15% measured for the precursor organic salt RBr. On the basis of our optical spectroscopy and computational work, the organic component is responsible for the observed blue emission of the hybrid material. In addition to the enhanced light emission efficiency, the novel hybrid indium bromide demonstrates significantly improved environmental stability. These findings may pave the way for the consideration of hybrid organic In(III) halides for light emission applications.

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Section: ■ Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Zero-Dimensional Hybrid Organic–Inorganic Indium Bromide with Blue Emission

et al. 2021

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“…The method is based on the nonrandom distribution between neutron detection times: the population of correlated prompt neutrons (those from the same fission chain seed) decays exponentially as fission chains extinguish [15]. Experimental results showed that the decay is modeled better by a two-exponential function than a one-exponential function when the assembly of fissile material is reflected [16,6], the model was theoretically derived from two-region point kinetics [17,18,11], and validated with a combination of experiments and simulations [12,19]. The two-exponential Rossi-alpha probability density function for reflected assemblies p R (τ) is given by…”

Section: Rossi-alpha Methodsmentioning

confidence: 99%

“…The detection system is identical to that of Refs. [19,12], which contain further details. A second OSCAR and two Neutron Multiplicity 3 He Array Detectors (NoMADs -15 3 He tubes embedded in a high-density polyethylene matrix [29]) were also present, all 47 cm from the center of the assembly, but data obtained from these systems are not used in this work.…”

Section: Methodsmentioning

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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“…[8]). The OSCAR prototype comprises 12, 5.08 cm × 5.08 cm diameter transstilbene crystals coupled to photomultiplier tubes [9,10,11], suspended in powder-coated iron wire meshes and held in place with porous polyurethane foam [12]. The detectors are powered with high voltage and pulses are digitized with a CAEN v1730 waveform digitizer (16 channels, 500-MHz sampling rate, 14-bit resolution, 2-V dynamic range).…”

Section: Measurement Specificationsmentioning

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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Rossi-alpha measurements of fast plutonium metal assemblies using organic scintillators

Cited by 15 publications

References 22 publications

Zero-Dimensional Hybrid Organic–Inorganic Indium Bromide with Blue Emission

Zero-Dimensional Hybrid Organic–Inorganic Indium Bromide with Blue Emission

On the Feynman-alpha Method for Reflected Fissile Assemblies

Simulation of the Nondestructive Assay of²³⁷Np Using Active Neutron Multiplicity Counting

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Rossi-alpha measurements of fast plutonium metal assemblies using organic scintillators

Cited by 15 publications

References 22 publications

Zero-Dimensional Hybrid Organic–Inorganic Indium Bromide with Blue Emission

Zero-Dimensional Hybrid Organic–Inorganic Indium Bromide with Blue Emission

On the Feynman-alpha Method for Reflected Fissile Assemblies

Simulation of the Nondestructive Assay of237Np Using Active Neutron Multiplicity Counting

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Product

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Simulation of the Nondestructive Assay of²³⁷Np Using Active Neutron Multiplicity Counting