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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Synthesis, structural and magnetic studies of the CuCr{sub 1-x}Rh{sub x}O{sub 2} delafossite solid solution with 0 {<=} x {<=} 0.2

Highlights: {yields} Rh non-magnetic replacement of the Cr in the magnetic frustrated delafossite CuCrO{sub 2}. {yields} Delafossite solid solution is maintained up to 0.2 in this system. {yields} Strain generated by Rh substitution is strongly anisotropic. {yields} M{sup 3+}-O bond strength is affected. {yields} High temperature paramagnetic behavior and weak ferromagnetism at low temperature. -- Abstract: The CuCr{sub 1-x}Rh{sub x}O{sub 2} series is investigated by X-ray diffraction, magnetization measurements and Raman spectroscopy on ceramic samples. It is found that a delafossite solid solution is maintained up to x = 0.2 in CuCr{sub 1-x}Rh{sub x}O{sub 2}. The small observed variation in cell parameters is consistent with the small difference between the ionic radii of Cr{sup 3+} and Rh{sup 3+}. A significant broadening of X-ray reflections is observed and when analyzed using the Williamson-Hall relationship showed that the strain generated by Rh substitution is strongly anisotropic, affecting mainly (Cr,Rh)-O bonds in the ab plane. Room temperature Raman spectra displayed three main Raman active modes. All modes shift to lower frequency and undergo significant changes in intensity with increasing Rh content, showing the effect of Rh atoms on the M{sup 3+}-O bond strength. The magnetic behavior of CuCr{sub 1-x}Rh{sub x}O{sub 2} samples was investigated as a function of temperature and applied field. At high temperature paramagnetic behavior, and at low temperature, evidence for weak ferromagnetism, reinforced by a hysteresis loop at 4 K is observed. The magnetic behavior of CuCr{sub 1-x}Rh{sub x}O{sub 2} is attributed to the disorder of Cr and Rh in octahedral sites resulting in short-range Cr-O-Cr and Cr-O-Rh interactions, which give rise to short-range weak ferromagnetism.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Effect of calcination temperature on structural and photocatalyst properties of nanofibers prepared from low-cost natural ilmenite mineral by simple hydrothermal method

Graphical abstract: - Highlights: • Nanofibers were prepared from low-cost ilmenite mineral via simple hydrothermal. • High photocatalyst nanofibers were prepared via post heat treatment method. • The nanofibers calcined at 100–700 °C for 2 h maintained nanofiber structure. • The calcined nanofibers at 400 °C showed the highest photocatalytic activity. - Abstract: Titanate nanofibers were synthesized via the hydrothermal method (120 °C for 72 h) using natural ilmenite mineral (FeTiO{sub 3}) as the starting material. The samples were characterized by X-ray diffraction (XRD), X-ray fluorescent (XRF), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) for specific surface area. The nanofibers were 20–90 nm in diameter and 2–7 μm in length. The as-synthesized nanofibers calcined at 300–400 °C showed TiO{sub 2} (B) whereas the nanofibers calcined at 500 °C revealed a mixture of two phases of TiO{sub 2} (B) and anatase. The nanofibers calcined at high temperature of 600–1000 °C showed a mixture of tri-crystalline of anatase, rutile, and Fe{sub 2}O{sub 3}. The rutile phase increased with increasing calcination temperature. The nanofibers calcined at 300–700 °C maintained their structure while the morphology of the nanofibers calcined at 800–1000 °C transformed into submicron rod-like structure. This increase of calcination temperature led to the phase transformation from thermodynamically metastable anatase to the most stable form of rutile phase. The crystallite size of prepared samples increased with increasing calcination temperature. Interestingly, with increasing calcination temperature, the absorption edge of the prepared samples shows an obvious shift to visible light region due to the change of crystallite phase and increased crystallite size. Therefore, the band gap energy of the prepared samples became narrower with increasing calcination temperature. Furthermore, the photocatalytic activity of the nanofibers calcined at 400 °C for 2 h was found to be not merely higher than those of the commercially available TiO{sub 2} nanoparticles powders (P-25, JRC-01, and JRC-03) but also the highest of all the samples in this study.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Preparation and characterization of bifunctional dendrimer modified Fe{sub 3}O{sub 4}/CdTe nanoparticles with both luminescent and superparamagnetic properties

Highlights: • The fluorescent superparamagnetic dendrimeric Fe{sub 3}O{sub 4}/CdTe nanoparticles are synthesized in this paper. • The synthesized nanocomposites maintain excellent magnetic properties. • The synthesized nanocomposites maintain highly luminescent markers with narrow emission bands. - Abstract: Magnetic nanoparticles Fe{sub 3}O{sub 4} were prepared by hydrothermal coprecipitation of ferric and ferrous ions using NaOH. The surface modification of Fe{sub 3}O{sub 4} nanoparticle by dendrimers has rendered the nanoparticle surface with enriched amine groups which facilitated the adsorption and conjugation of thioglycolic acid (TGA) modified CdTe quantum dots to form a stable hybrid nanostructure. Three generations (first generation: G0F, second generation: G1F, third generation: G3F) of bifunctional dendrimeric Fe{sub 3}O{sub 4}/CdTe nanoparticles were successfully prepared using this technique and characterized by microscopy. The optical and magnetic properties of the dendrimeric Fe{sub 3}O{sub 4}/CdTe nanoparticle were also investigated. The microscopic study reveals 3 different sizes for 3 generations, 16 nm (G0F), 31 nm (G1F) and 47 nm (G3F). Among three generations of nanoparticles, the G1F has the best optical property with a luminescent quantum yield of 25.6% and the G0F has the best magnetic property with a saturation magnetization of 19.3 emμ/g.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Electrochemical properties of Sn-based nanopowders synthesized by a pulsed wire evaporation method and effect of binder coating

Highlights: • Sn-based nanoparticles are fabricated by using the pulsed wire evaporation method. • The electrodes are prepared by mixing the graphene and coating the surface. • Coating the surface of electrode is used with brushing of simple and facile method. • The electrochemical measurements are performed with galvanostatic experiments. • The coating electrode maintains capacity nearly of 501 mAh g{sup −1} up to 100 cycles. - Abstract: Sn-based nanoparticles are prepared with the O{sub 2} concentrations in chamber of Ar atmosphere (by v/v) by using the pulsed wire evaporation (PWE) method. The prepared electrodes are only Sn-based powder electrode, its binder coating electrode and Sn-based powder/graphene nanocomposite electrode. Morphology and structure of the synthesized powders and electrodes are investigated with a field emission scanning electron microscope (FE-SEM) and an X-ray diffraction (XRD) analysis. The electrochemical measurements were performed with galvanostatic cycling experiments using a coin type cell of CR2032 (Ø20, T3.2 mm). The binder coating electrode is superior to others and maintains delithiation capacity nearly of 501 mAh g{sup −1} as 58.3% of first delithiation capacity at 0.2 C-rate up to 100 cycles.

36 MATERIALS SCIENCE↗
DOE OSTI2016

A novel fabrication of Cu{sub 2}O@Cu{sub 7}S{sub 4} core-shell micro/nanocrystals from Cu{sub 2}O temples and enhanced photocatalytic activities

Highlights: • The Cu{sub 2}O@Cu{sub 7}S{sub 4} core-shell crystals maintained the same morphology with template. • The crystals exhibit enhanced photocatalytic activity than the pure Cu{sub 2}O crystals. • The photocatalytic activity of different R crystals is diverse from each other. • A possible formation mechanism has been proposed. - Abstract: Uniform and monodispersed Cu{sub 2}O@Cu{sub 7}S{sub 4} core-shell micro/nanocrystals have been synthesized successfully at room temperature via a simple chemical etching reaction, using Cu{sub 2}O as sacrificial template. The structure and properties of the crystals were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS). The photocatalytic activity of the Cu{sub 2}O@Cu{sub 7}S{sub 4} crystals was evaluated by photocatalytic decolorization of MeO (methyl orange) aqueous solution at ambient temperature under visible-light irradiation. The results show that the as-prepared Cu{sub 2}O@Cu{sub 7}S{sub 4} crystals revealed core-shell structure, which maintained the same morphology with corresponding template and were composed of cuboctahedron Cu{sub 7}S{sub 4} shell and active Cu{sub 2}O core. Due to the unique Cu{sub 2}O@Cu{sub 7}S{sub 4} core-shell structure, the crystals exhibit enhanced photocatalytic activity than that of the pure Cu{sub 2}O crystals, and the photocatalytic activity of different R crystals is diverse from each other. A possible formation mechanism has been proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2024

One-pot synthesis of mechanically robust hierarchical graphene-polyethylene aerogels

Fabricating mechanically robust graphene aerogels (GAs) without compromising their notable features including superelasticity, large surface area, high porosity, and low density is challenging. Here, this work presents a new one-pot strategy based on ambient drying to fabricate a three-dimensional (3D) graphene-polyethylene aerogel (G-PEA) with a unique hierarchical porous structure, in which the highly porous polyethylene is encapsulated by graphene frameworks. The hierarchical G-PEA exhibited substantially enhanced compressive strength while maintaining low density and superelasticity comparable to those of bare GAs. The G-PEAs with 5 wt% PE (G-PEA5) showed a significant improvement (up to 2083 %) in compressive stress compared to bare GAs, which can be attributed to the porous PE support within the GA framework. The G-PEA5 retained 94% of its compressive stress after 100 compression cycles, which is still higher than that (∼80%) of bare GAs, and maintained good elastic recovery. The designed hierarchical G-PEAs show great promise in the applications that require outstanding mechanical properties.

Composite↗
DOE OSTI2020

Ultrahigh coulombic efficiency electrolyte enables Li||SPAN batteries with superior cycling performance

Raising the coulombic efficiency of lithium metal anode cycling is the deciding step in realizing long-life rechargeable lithium batteries. Here, we designed a highly concentrated salt/ether electrolyte diluted in a fluorinated ether: 1.8 M LiFSI in DEE/BTFE (diethyl ether/bis(2,2,2-trifluoroethyl)ether), which realized an average coulombic efficiency of 99.37% at 0.5 mA cm -2 and 1 mAh cm -2 for more than 900 cycles. This electrolyte also maintained a record coulombic efficiency of 98.7% at 10 mA cm -2 , indicative of its ability to provide fast-charging with high cathode loadings. Morphological studies reveal dense, dendrite free Li depositions after prolonged cycling, while surface analyses confirmed the formation of a robust LiF-rich SEI layer on the cycled Li surface. Moreover, we discovered that this ether-based electrolyte is highly compatible with the low-cost, high-capacity SPAN (Sulfurized polyacrylonitrile) cathode, where the constructed Li||SPAN cell exhibited reversible cathode capacity of 579 mAh g -1 and no capacity decay after 1200 cycles. A cell where a high areal loading SPAN electrode (>3.5 mAh cm -2 ) is paired with only onefold excess Li was constructed and cycled at 1.75 mA cm -2 , maintaining a coulombic efficiency of 99.30% for the lithium metal. Computational simulations revealed that at saturation, the Li-FSI complex forms contact ion pairs, with a first solvation shell comprising DEE molecules, and a second solvation shell with a mix of DEE/BTFE. This study provides a path to enable high energy density Li||SPAN batteries with stable cycling.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Anatomic and Dosimetric Changes During the Treatment Course of Intensity-Modulated Radiotherapy for Locally Advanced Nasopharyngeal Carcinoma

Many patients with nasopharyngeal carcinoma (NPC) have marked anatomic change during intensity-modulated radiation therapy (IMRT). In this study, the magnitude of anatomic changes and its dosimetric effects were quantified. Fifteen patients with locally advanced NPC treated with IMRT had repeated computed tomography (CT) after 18 fractions. A hybrid plan was made to the anatomy of the second computed tomography scan. The dose of the original plan, hybrid plan, and new plan were compared. The mean volume of left and right parotid decreased 6.19 mL and 6.44 mL, respectively. The transverse diameters of the upper bound of odontoid process, the center of odontoid process, and the center of C2 vertebral body slices contracted with the mean contraction of 8.2 mm, 9.4 mm, and 7.6 mm. Comparing the hybrid plan with the treatment plan, the coverage of target was maintained while the maximum dose to the brain stem and spinal cord increased by 0.08 to 6.51 Gy and 0.05 to 7.8 Gy. The mean dose to left and right parotid increased by 2.97 Gy and 2.57 Gy, respectively. A new plan reduced the dose of spinal cord, brain stem, and parotids. Measurable anatomic changes occurring during the IMRT for locally advanced NPC maintained the coverage of targets but increased the dose to critical organs. Those patients might benefit from replanning.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2022

Joining technique for in-oven/autoclave molds manufactured by large scale polymer additive manufacturing

Large scale additive manufacturing (AM) of fiber-reinforced polymer composites has gained traction in the mold and die community over the last decade, largely due to reduced material cost and lead time. However, limitations in mold size remain present due to printer volume constraints and costs associated with large format machines. Here, this paper describes a method for producing additively manufactured polymer molds in segments with an O-ring joint design, which can be machined and subsequently assembled for autoclave applications. The developed joining mechanism allows for maintaining the vacuum integrity during the cure cycle while accounting for the anisotropic nature of the additively manufactured polymer molds. Over a range of tested temperatures, 20–200 °C, the multi-part mold joining design was able to achieve full vacuum of ∼73.7 cmHg (29 inchHg) and maintain a vacuum integrity with vacuum losses less than 1.5 cmHg/5min (0.6 inchHg).

Joining↗
DOE OSTI2016

Modified inverse micelle synthesis for mesoporous alumina with a high D4 siloxane adsorption capacity

In this work, mesoporous aluminas (MAs) with uniform and monomodal pores were fabricated via a modified inverse micelle synthesis method, using a non-polar solvent (to minimize the effect of water content) and short reaction time (for a fast evaporation process). The effects of reaction times (4–8 h), surfactant chain lengths (non-ionic surfactants), and calcination temperatures and hold times (450–600 °C; 1–4 h) on the textural properties of MA were studied. Additionally, the targeted pore sizes of MA were obtained in the range of 3.1–5.4 nm by adjusting the surfactant and reaction time. The surface area and pore volume were controlled by the calcination temperature and hold time while maintaining the thermal stability of the materials. The tuned MA of the large mesopore volume achieved 168 mg/g octamethylcyclotetrasiloxane (D4 siloxane) adsorption capacity, a 32% improvement compared to commercially activated alumina. Finally, after three adsorption recycles, the synthesized MA still maintained approximate 85% of its original adsorption capacity, demonstrating a sustainable adsorption performance and high potential for related industrial applications.

25 ENERGY STORAGE↗
DOE OSTI2021

Crowded electrolytes containing redoxmers in different states of charge: Solution structure, properties, and fundamental limits on energy density

Nonaqueous redox flow batteries use liquid electrolytes containing redox-active organic molecules (redoxmers) as their energy storage medium. To maximize energy density, the redoxmer concentration needs to be maximized while maintaining low viscosity and high ionic conductivity. During charge, a redoxmer molecule pairs with an ion in the electrolyte while another ion migrates across the membrane to maintain electric neutrality. In a crowded electrolyte, this reconstitution changes physical and chemical properties of the solution. To explore these behaviors, a phenothiazine redoxmer fully miscible with acetonitrile was used, and electrochemical charge was mimicked by chemical oxidation. The solutions were examined using small-angle X-ray scattering, nuclear magnetic resonance, and conductometry and modeled using classical molecular dynamics. Overall, our study indicates that physical and structural properties of redoxmer solutions in both states of charge make it exceedingly difficult to increase the redoxmer concentrations over 2 M at any temperature without compromising dynamic properties of such solutions. The cause for this limitation is proximity to a gel-like regime in which fluidity, diffusivity, and ionic conductivity exponentially decrease with increasing concentration. This tendency is compounded by non-Arrhenius behavior of the electrolyte: a small increase in the concentration outruns gains in fluidity and conductivity at a higher temperature. Thus the properties of crowded electrolytes generally make it impossible to operate when gel-like behavior sets in. Pushing the redoxmer concentration to 2.5-3 M might be possible for small redoxmer molecules, but it would require the use of ionic liquid electrolytes at 340-360 K. (C) 2021 Elsevier B.V. All rights reserved.

25 ENERGY STORAGE↗
DOE OSTI2018

Role of structural hydroxyl groups in enhancing performance of electrochemically-synthesized bilayer V 2 O 5

Nanostructured electrode materials represent a promising path forward to dramatically improving the performance of both Li-ion and beyond Li-ion battery systems; however, difficulties in characterizing the structural and electrochemical changes that take place in nanoscale systems, which are often poorly crystalline or amorphous, make it difficult to develop design rules for synthesizing new materials with optimal performance. Bilayered vanadium oxide-based materials (BL-V 2 O 5 ) are an ideal platform for understanding the underlying physicochemical properties that determine capacity in nanomaterials, with electrochemically-synthesized V 2 O 5 (EC-V 2 O 5 ) exhibiting particularly high capacities. In this work we provide evidence that the source of high practical capacity in EC-V 2 O 5 is the presence of “structural hydroxyl groups” that are an intrinsic feature of the electrochemical synthesis method. Using both in situ and ex situ characterization methods, we demonstrate that structural OH species are highly stable and persist in the structure during reversible cycling. We hypothesize three important roles for structural OH groups: they maintain a sufficient interlayer spacing to allow the physical diffusion of cations over multiple cycles; they maintain a consistent solvating environment in the bilayer regardless of structural H 2 O content; and they reduce the symmetry of vanadium polyhedra to favor electron transfer over pseudocapacitive adsorption, making it possible to access close to theoretical capacity. Furthermore, these insights have broad implications for understanding the performance of a variety of hydrated oxide systems, and indicate that the formation of covalently-bound hydroxyoxide species can lead to further improvements in the performance of nanoscale materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

ENDF/B-VII.1 Nuclear Data for Science and Technology: Cross Sections, Covariances, Fission Product Yields and Decay Data

The ENDF/B-VII.1 library is our latest recommended evaluated nuclear data file for use in nuclear science and technology applications, and incorporates advances made in the five years since the release of ENDF/B-VII.0. These advances focus on neutron cross sections, covariances, fission product yields and decay data, and represent work by the US Cross Section Evaluation Working Group (CSEWG) in nuclear data evaluation that utilizes developments in nuclear theory, modeling, simulation, and experiment. The principal advances in the new library are: (1) An increase in the breadth of neutron reaction cross section coverage, extending from 393 nuclides to 423 nuclides; (2) Covariance uncertainty data for 190 of the most important nuclides, as documented in companion papers in this edition; (3) R-matrix analyses of neutron reactions on light nuclei, including isotopes of He, Li, and Be; (4) Resonance parameter analyses at lower energies and statistical high energy reactions for isotopes of Cl, K, Ti, V, Mn, Cr, Ni, Zr and W; (5) Modifications to thermal neutron reactions on fission products (isotopes of Mo, Tc, Rh, Ag, Cs, Nd, Sm, Eu) and neutron absorber materials (Cd, Gd); (6) Improved minor actinide evaluations for isotopes of U, Np, Pu, and Am (we are not making changes to the major actinides {sup 235,238}U and {sup 239}Pu at this point, except for delayed neutron data and covariances, and instead we intend to update them after a further period of research in experiment and theory), and our adoption of JENDL-4.0 evaluations for isotopes of Cm, Bk, Cf, Es, Fm, and some other minor actinides; (7) Fission energy release evaluations; (8) Fission product yield advances for fission-spectrum neutrons and 14 MeV neutrons incident on {sup 239}Pu; and (9) A new decay data sublibrary. Integral validation testing of the ENDF/B-VII.1 library is provided for a variety of quantities: For nuclear criticality, the VII.1 library maintains the generally-good performance seen for VII.0 for a wide range of MCNP simulations of criticality benchmarks, with improved performance coming from new structural material evaluations, especially for Ti, Mn, Cr, Zr and W. For Be we see some improvements although the fast assembly data appear to be mutually inconsistent. Actinide cross section updates are also assessed through comparisons of fission and capture reaction rate measurements in critical assemblies and fast reactors, and improvements are evident. Maxwellian-averaged capture cross sections at 30 keV are also provided for astrophysics applications. We describe the cross section evaluations that have been updated for ENDF/B-VII.1 and the measured data and calculations that motivated the changes, and therefore this paper augments the ENDF/B-VII.0 publication 'ENDF/B-VII.0: Next Generation Evaluated Nuclear Data Library for Nuclear Science and Technology,' Nuclear Data Sheets 107, 2931 (2006).

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2014

Towards a More Complete and Accurate Experimental Nuclear Reaction Data Library (EXFOR): International Collaboration Between Nuclear Reaction Data Centres (NRDC)

The International Network of Nuclear Reaction Data Centres (NRDC) coordinated by the IAEA Nuclear Data Section (NDS) successfully collaborates in the maintenance and development of the EXFOR library. As the scope of published data expands (e.g. to higher energy, to heavier projectile) to meet the needs of research and applications, it has become a challenging task to maintain both the completeness and accuracy of the EXFOR library. Evolution of the library highlighting recent developments is described.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Linear models to perform treaty verification tasks for enhanced information security

Linear mathematical models were applied to binary-discrimination tasks relevant to arms control verification measurements in which a host party wishes to convince a monitoring party that an item is or is not treaty accountable. These models process data in list-mode format and can compensate for the presence of variability in the source, such as uncertain object orientation and location. The Hotelling observer applies an optimal set of weights to binned detector data, yielding a test statistic that is thresholded to make a decision. The channelized Hotelling observer applies a channelizing matrix to the vectorized data, resulting in a lower dimensional vector available to the monitor to make decisions. We demonstrate how incorporating additional terms in this channelizing-matrix optimization offers benefits for treaty verification. We present two methods to increase shared information and trust between the host and monitor. The first method penalizes individual channel performance in order to maximize the information available to the monitor while maintaining optimal performance. Second, we present a method that penalizes predefined sensitive information while maintaining the capability to discriminate between binary choices. Data used in this study was generated using Monte Carlo simulations for fission neutrons, accomplished with the GEANT4 toolkit. Custom models for plutonium inspection objects were measured in simulation by a radiation imaging system. Model performance was evaluated and presented using the area under the receiver operating characteristic curve.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

Capacitively coupled pickup in MCP-based photodetectors using a conductive metallic anode

We have designed and tested a robust 20×20 cm 2 thin metal film internal anode capacitively coupled to an external array of signal pads or micro-strips for use in fast microchannel plate photodetectors. The internal anode, in this case a 10 nm-thick NiCr film deposited on a 96% pure Al 2 O 3 3 mm-thick ceramic plate and connected to HV ground, provides the return path for the electron cascade charge. The multi-channel pickup array consists of a printed-circuit card or glass plate with metal signal pickups on one side and the signal ground plane on the other. The pickup can be put in close proximity to the bottom outer surface of the sealed photodetector, with no electrical connections through the photodetector hermetic vacuum package other than a single ground connection to the internal anode. Two pickup patterns were tested using a small commercial MCP-PMT as the signal source: 1) parallel 50 Ω 25-cm-long micro-strips with an analog bandwidth of 1.5 GHz, and 2) a 20×20 cm 2 array of 2-dimensional square ‘pads’ with sides of 1.27 cm or 2.54 cm. The rise-time of the fast input pulse is maintained for both pickup patterns. For the pad pattern, we observe 80% of the directly coupled amplitude. For the strip pattern we measure 34% of the directly coupled amplitude on the central strip of a broadened signal. The physical decoupling of the photodetector from the pickup pattern allows easy customization for different applications while maintaining high analog bandwidth.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Development and evaluation of a list mode neutron coincidence collar for spatial response measurements of fresh fuel assemblies

A traditional safeguards neutron coincidence counting system, the Neutron Coincidence Collar, has been modified to incorporate individual preamplifiers on each of its 18 3He tubes in active interrogation mode. When used with list mode data acquisition (LMDA) and analysis, a signal from each 3He tube can be recorded and analyzed to allow a spatial response measurement to be performed on an item based on count rate and 3He tube location within the system. The ultimate goal of this project is to demonstrate the capabilities of a list mode response matrix for the nondestructive assay of fresh nuclear fuel assemblies. To enable partial defect detection of fuel pin locations and absences within an assembly, the project aims to extend well-established correlated neutron analysis techniques on a preexisting Neutron Coincidence Collar by extracting a greater number of useful signatures from the system than are currently generated. LMDA, combined with the addition of multiple preamplifiers, facilitates this capability by increasing the number of simultaneous signals that can be measured; this allows an in-depth analysis of neutron coincidence events to determine a fissioning item’s location based on the measured doubles count rate in various channel logic coincidence combinations. All of this can be done from a single measurement pulse train in offline analysis, which is the major benefit provided by LMDA. Through various stages of development and testing, a Mirion Technologies model JCC-71 Neutron Coincidence Collar has been successfully retrofit with modern electronics designed in-house at Oak Ridge National Laboratory, matching preexisting JAB-01 electronics performance, while maintaining the original system footprint. This paper presents these various stages of development and experimental evaluation of the proof of concept system.

Moore, Angela S.↗
DOE OSTI2021

Performance characterization of the Radionuclide Aerosol Sampler/Analyzer air sampler during a high-activity release event

The performance of the Radionuclide Aerosol Sampler/Analyzer (RASA) under high-activity conditions has been evaluated to maintain and protect the operations of International Monitoring System (IMS) radionuclide stations. Station measurements following the Fukushima Daichi accident of 11 March 2011 have been combined with laboratory measurements to understand how the quality of the measurements made using the RASA High-Purity Germanium (HPGe) gamma-spectrometer are impacted by increased sample activity and detector dead-time. Detector saturation has been identified to occur at a count rate of 175,000 counts s-1, at which level there are significant impacts to the sample live-time and detector resolution in addition to a system contamination risk. To safeguard against these effects, a dead-time limit of 16.6% is proposed that could be maintained by monitoring the activity collecting on the filter using a Cadmium Zinc Telluride (CZT) detector installed into the particulate collection area of the RASA. This limit would ensure that the IMS technical specifications for measurement time (> 20 h) and detector resolution (2.5 keV at 1332 keV) are met. The CZT would dynamically control the RASA air flow to limit the collection of particulate activity beneath the HPGe dead-time threshold and would also provide measurements useful for CTBT verification purposes and dose assessments.

Burnett, Jonathan L.↗