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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 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Extension of the Dytlewski-style dead time correction formalism for neutron multiplicity counting to any order

Here, neutron multiplicity counting using shift-register calculus is an established technique in the science of international nuclear safeguards for the identification, verification, and assay of special nuclear materials. Typically passive counting is used for Pu and mixed Pu-U items and active methods are used for U materials. Three measured counting rates, singles, doubles and triples are measured and, in combination with a simple analytical point-model, are used to calculate characteristics of the measurement item in terms of known detector and nuclear parameters. However, the measurement problem usually involves more than three quantities of interest, but even in cases where the next higher order count rate, quads, is statistically viable, it is not quantitatively applied because corrections for dead time losses are currently not available in the predominant analysis paradigm. In this work we overcome this limitation by extending the commonly used dead time correction method, developed by Dytlewski, to quads. We also give results for pents, which may be of interest for certain special investigations. Extension to still higher orders, may be accomplished by inspection based on the sequence presented. We discuss the foundations of the Dytlewski method, give limiting cases, and highlight the opportunities and implications that these new results expose. In particular there exist a number of ways in which the new results may be combined with other approaches to extract the correlated rates, and this leads to various practical implementations.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Residual strain mapping of Roman styli from Iulia Concordia, Italy

Iulia Concordia is an important Roman settlement known for the production of iron objects and weapons during the Roman Empire. A huge number of well-preserved styli were found in the past century in the bed of an old channel. In order to shed light about the production processes used by Roman for stylus manufacturing, a neutron diffraction residual strain analysis was performed on the POLDI materials science diffractometer at the Paul Scherrer Institut in Switzerland. Here, we present results from our investigation conducted on 11 samples, allowing to define, in a non-invasive way, the residual strain map related to the ancient Roman working techniques. - Highlights: • We examined 11 Roman styli from the settlement of Iulia Concordia, Italy. • We performed a neutron diffraction residual strain analysis on POLDI at PSI (CH). • We identified the production processes used by Roman for stylus manufacturing. • We clarified the way and direction of working applied for different classes of styli.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Applications of C 7 LYC scintillators in fast neutron spectroscopy

Here, the capabilities of 7 Li-enriched Cs 2 7 LiYCl 6 (C 7 LYC) scintillation detectors for fast neutron spectroscopy are explored in benchmark experiments that exploit its excellent pulse-shape discrimination between neutrons and γ rays, and its unprecedented ≈10% energy resolution for fast neutrons in the few MeV range, obtained through the 35 Cl(n,p) reaction. Energy- and angle-resolved elastic and inelastic neutron scattering cross-section measurements of 56 Fe(n,n’) were performed at Los Alamos National Laboratory with a pulsed white neutron source and an array of 1" x 1" C 7 LYC crystals. The results convincingly establish the utility of this dual n/γ scintillator for fast neutron spectroscopy. Intrinsic efficiency measurements of both 1" x 1" and the first ever 3" x 3" C 7 LYC crystal have been initiated, using mono-energetic fast neutron beams at UMass Lowell generated via the 7 Li(p,n) reaction. Finally, the spectroscopic capabilities and potential of C 7 LYC are discussed in the context of developing this emerging scintillator for targeted science applications.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS2001

Estimation of neutron and other radiation exposure components in low earth orbit

The interaction of high-energy space radiation with spacecraft materials generates a host of secondary particles, some, such as neutrons, are more biologically damaging and penetrating than the original primary particles. Before committing astronauts to long term exposure in such high radiation environments, a quantitative understanding of the exposure and estimates of the associated risks are required. Energetic neutrons are traditionally difficult to measure due to their neutral charge. Measurement methods have been limited by mass and weight requirements in space to nuclear emulsion, activation foils, a limited number of Bonner spheres, and TEPCs. Such measurements have had limited success in quantifying the neutron component relative to the charged components. We will show that a combination of computational models and experimental measurements can be used as a quantitative tool to evaluate the radiation environment within the Shuttle, including neutrons. Comparisons with space measurements are made with special emphasis on neutron sensitive and insensitive devices. c2001 Elsevier Science Ltd. All rights reserved.

STS-57 Shuttle Project↗
DOE OSTI2024

Relative sensitivity of plastic scintillator: A comparative analysis with 60 Co gamma rays, deuterium–deuterium, and deuterium–tritium neutrons

A plastic scintillator has found extensive application in the realm of high-energy physics and national security science. Many applications in those fields often involve the simultaneous production of photons, neutrons, and charged particles, which makes the relative sensitivity information for these different radiation types important. In this study, we have adopted a multi-head detector comprised of a plastic scintillator and high gain phototubes, which provides a large dynamic range and linearity. A comparative study on the relative sensitivities of plastic scintillators was facilitated by adopting three distinct radiation calibration sources (i.e., 60 Co γ rays, DD neutrons, and DT neutrons). Neutrons from a DD source generate a comparable level of scintillation to gamma rays emitted by 60 Co (i.e., 60 Co-γ/DD-n = 0.92 ± 16%). DT neutrons induce ~3.5 times the scintillation observed with DD neutrons (i.e., DT-n/DD-n = 3.5 ± 28%). In addition, the Geant4 simulation granted us valuable insights into the relative sensitivity of the scintillator. This comparative study will provide a useful database for users in diverse applications.

47 OTHER INSTRUMENTATION↗
DOE OSTI2016

Investigation of Energy Selective Neutron Imaging at the PULSTAR Reactor

Neutron imaging is complementary to X-ray imaging where both are used to investigate the internal features of objects nondestructively. Historically, it only began three years after discovery of the neutron in 1932, however, neutron radiographs with reasonable quality were first made in the mid-fifties. Conventionally, the image is produced by placing the object between the neutron source and a two-dimensional position sensitive detector. The source commonly has a full energy spectrum (white beam) of thermal or cold neutrons to obtain high intensity in the sample and short exposure time. As a result, all neutron energies contribute to the obtained radiograph. Since the interaction of the neutron with matter is energy dependent, different energies produce different contrast on the radiographic image, hence, additional information about the object can be obtained. Neutron imaging that utilizes a narrow spectrum of energy instead of white beam is called energy selective neutron imaging. Many techniques have been explored to select a narrow band of neutron energy for the use in imaging such as the use velocity selectors, double crystal Monochromators, and time of flight techniques (at pulsed neutron sources). The PULSTAR reactor of North Carolina State University (1 MWth) currently has an operational neutron powder diffractometer (NPD) installed on beam tube no. 4, which was designed for neutron scattering experiments and can provide a monoenergetic beam of neutrons. The neutron energy could be selected by diffraction means using a Si bent perfect crystal as a Monochromator. In this work, an investigation of energy selective neutron imaging at the NPD is discussed in terms of the system performance and the ability of material discrimination on a test sample by observing the contrast variations of the neutron radiographs obtained using different neutron energies. Energy selective neutron imaging experiment was successfully tested at the PULSTAR reactor's NPD. Although, the uniform region is small and the exposure time is long in comparison with the NIF, both facilities exhibit similar spatial resolution which is a very important characteristic for any imaging facility. The contrast variation of neuron radiographs for the test sample obtained at different energies indicated a potential advantage for using energy selective neutron imaging over the white beam. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2019

Implementation and assessment of resolution-dependent elastic incoherent neutron scattering measurements at a backscattering spectrometer for probing relaxations in complex systems

We introduce the use of a higher-order reflection, Si(333), of the silicon analyzer crystals at a backscattering spectrometer to implement analysis of the relaxation dynamics in the samples. Here, this is achieved by monitoring the temperature dependence of the neutron scattering intensity perceived as elastic when measured using Si(111), Si(311), and Si(333) reflections. As a test case, we use a sample with well-characterized, but complex, relaxation pattern, where the non-Lorentzian relaxation function is known to exhibit a set of parameters specific to each temperature point and scattering momentum transfer (Q) value. Even for this very general relaxation pattern, characterized by no constrains on the relaxation function parameters, we successfully map the relaxation times measured using the present approach onto those previously obtained from the full analysis of the quasielastic neutron scattering signal. Analysis of the Q-specific activation energies becomes possible for the Q values accessible simultaneously through Si(111), Si(311), and Si(333) reflections (in the present case, 0.9 Å –1 < Q < 1.9 Å –1 ). While the dedicated neutron spectrometers for this type of analysis are yet to be constructed, we show that the present-day backscattering spectrometers can be employed, under certain conditions, to analyze temperature dependence of the relaxation time in the samples not amenable to traditional full analysis of the quasielastic neutron scattering signal.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Calibration of ITER Instant Power Neutron Monitors: Recommended Scenario of Experiments at the Reactor

Instant power is a key parameter of the ITER. Its monitoring with an accuracy of a few percent is an urgent and challenging aspect of neutron diagnostics. In a series of works published in Problems of Atomic Science and Technology, Series: Thermonuclear Fusion under a common title, the step-by-step neutronics analysis was given to substantiate a calibration technique for the DT and DD modes of the ITER. A Gauss quadrature scheme, optimal for processing “expensive” experiments, is used for numerical integration of {sup 235}U and {sup 238}U detector responses to the point sources of 14-MeV neutrons. This approach allows controlling the integration accuracy in relation to the number of coordinate mesh points and thus minimizing the number of irradiations at the given uncertainty of the full monitor response. In the previous works, responses of the divertor and blanket monitors to the isotropic point sources of DT and DD neutrons in the plasma profile and to the models of real sources were calculated within the ITER model using the MCNP code. The neutronics analyses have allowed formulating the basic principles of calibration that are optimal for having the maximum accuracy at the minimum duration of in situ experiments at the reactor. In this work, scenarios of the preliminary and basic experimental ITER runs are suggested on the basis of those principles. It is proposed to calibrate the monitors only with DT neutrons and use correction factors to the DT mode calibration for the DD mode. It is reasonable to perform full calibration only with {sup 235}U chambers and calibrate {sup 238}U chambers by responses of the {sup 235}U chambers during reactor operation (cross-calibration). The divertor monitor can be calibrated using both direct measurement of responses at the Gauss positions of a point source and simplified techniques based on the concepts of equivalent ring sources and inverse response distributions, which will considerably reduce the amount of measurements. It is shown that the monitor based on the average responses of the horizontal and vertical neutron chambers remains spatially stable as the source moves and can be used in addition to the staff monitor at neutron fluxes in the detectors four orders of magnitude lower than on the first wall, where staff detectors are located. Owing to low background, detectors of neutron chambers do not need calibration in the reactor because it is actually determination of the absolute detector efficiency for 14-MeV neutrons, which is a routine out-of-reactor procedure.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Computational Workflows for Uncertainty-Quantified Nuclear Reactions: From Nuclear Theory Inputs to Astrophysical Reaction Rates

Reactions on unstable nuclei, particularly those on the neutron-rich side of stability, are important for both fundamental and applied physics. For fundamental science, the most prevalent use case is astrophysi cal nucleosynthesis by rapid neutron capture—the r-process—by which heavy nuclei are formed in extreme astrophysical environments, such as in supernovae and neutron star mergers; see, e.g., Refs. [1–3]. For ap plications, these processes are relevant for the interpretation of radiochemical data from historic nuclear tests, which contribute to our ability to certify the enduring stockpile in the absence of nuclear testing [4]; see Ref. [5] for a broader discussion of applications. However, reaction cross sections involving unsta ble species are generally poorly understood, for the simple reason that useful data become scarce as one moves away from stability. While there are avenues for improving the amount and quality of data for these species [6], one is fundamentally reliant on nuclear theory to make progress on these fields of study.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Multiplicity counting using organic scintillators to distinguish neutron sources: An advanced teaching laboratory

In this advanced instructional laboratory, students explore complex detection systems and nondestructive assay techniques used in the field of nuclear physics. After setting up and calibrating a neutron detection system, students carry out timing and energy deposition analyses of radiation signals. Through the timing of prompt fission neutron signals, multiplicity counting is used to carry out a special nuclear material (SNM) nondestructive assay. Our experimental setup is comprised of eight trans-stilbene organic scintillation detectors in a well-counter configuration, and measurements are taken on a spontaneous fission source as well as two (α,n) sources. By comparing each source's measured multiplicity distribution, the resulting measurements of the (α,n) sources can be distinguished from that of the spontaneous fission source. Such comparisons prevent the spoofing, i.e., intentional imitation, of a fission source by an (α,n) neutron source. This instructional laboratory is designed for nuclear engineering and physics students interested in organic scintillators, neutron sources, and nonproliferation radiation measurement techniques.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

KGK-2-type detector of gamma-radiation power for diagnosis of nuclear reactor radiation fields within the range from 1 µGy/s to 100 Gy/s

The construction of the KGK-2-type detector of γ-radiation power is briefly described. The diagnostic possibilities of the detector are shown by the example of results of the dose rate measurement in the energy start-ups of the BR-K1 and BR-1M reactors implemented in the mode of generating fission pulses on delayed neutrons. The possibilities of using the KGK-2 detector for postpulse γ diagnostics are demonstrated by the example of results of measurements in the fission pulse on prompt neutrons of the BR-1M reactor.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2015

Novel method for detecting the hadronic component of extensive air showers

A novel method for studying the hadronic component of extensive air showers (EAS) is proposed. The method is based on recording thermal neutrons accompanying EAS with en-detectors that are sensitive to two EAS components: an electromagnetic (e) component and a hadron component in the form of neutrons (n). In contrast to hadron calorimeters used in some arrays, the proposed method makes it possible to record the hadronic component over the whole area of the array. The efficiency of a prototype array that consists of 32 en-detectors was tested for a long time, and some parameters of the neutron EAS component were determined.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS2016

Resource Prospector Instrumentation for Lunar Volatiles Prospecting, Sample Acquisition and Processing

Data gathered from lunar missions within the last two decades have significantly enhanced our understanding of the volatile resources available on the lunar surface, specifically focusing on the polar regions. Several orbiting missions such as Clementine and Lunar Prospector have suggested the presence of volatile ices and enhanced hydrogen concentrations in the permanently shadowed regions of the moon. The Lunar Crater Observation and Sensing Satellite (LCROSS) mission was the first to provide direct measurement of water ice in a permanently shadowed region. These missions with other orbiting assets have laid the groundwork for the next step in the exploration of the lunar surface; providing ground truth data of the volatiles by mapping the distribution and processing lunar regolith for resource extraction. This next step is the robotic mission Resource Prospector (RP). Resource Prospector is a lunar mission to investigate 'strategic knowledge gaps' (SKGs) for in-situ resource utilization (ISRU). The mission is proposed to land in the lunar south pole near a permanently shadowed crater. The landing site will be determined by the science team with input from broader international community as being near traversable landscape that has a high potential of containing elevated concentrations of volatiles such as water while maximizing mission duration. A rover will host the Regolith & Environment Science and Oxygen & Lunar Volatile Extraction (RESOLVE) payload for resource mapping and processing. The science instruments on the payload include a 1-meter drill, neutron spectrometer, a near infrared spectrometer, an operations camera, and a reactor with a gas chromatograph-mass spectrometer for volatile analysis. After the RP lander safely delivers the rover to the lunar surface, the science team will guide the rover team on the first traverse plan. The neutron spectrometer (NS) and near infrared (NIR) spectrometer instruments will be used as prospecting tools to guide the traverse path. The NS will map the water-equivalent hydrogen concentration as low as 0.5% by weight to an 80 centimeter depth as the rover traverses the lunar landscape. The NIR spectrometer will measure surficial H2O/OH as well as general mineralogy. When the prospecting instruments identify a potential volatile-rich area during the course of a traverse, the prospect is then mapped out and the most promising location identified. An augering drill capable of sampling to a depth of 100 centimeters will excavate regolith for analysis. A quick assay of the drill cuttings will be made using an operations camera and NIR spectrometer. With the water depth confirmed by this first auguring activity, a regolith sample may be extracted for processing. The drill will deliver the regolith sample to a crucible that will be sealed and heated. Evolved volatiles will be measured by a gas chromatograph-mass spectrometer and the water will be captured and photographed. RP is a solar powered mission, which given the polar location translates to a relatively short mission duration on the order of 4-15 days. This short mission duration drives the concept of operations, instrumentation, and data analysis towards critical real time analysis and decision support. Previous payload field tests have increased the fidelity of the hardware, software, and mission operations. Current activities include a mission level field test to optimize interfaces between the payload and rover as well as better understand the interaction of the science and rover teams during the mission timeline. This paper will include the current status of the science instruments on the payload as well as the integrated field test occurring in fall of 2015. The concept of operations will be discussed, including the real time science and engineering decision-making process based on the critical data from the instrumentation. The path to flight will be discussed with the approach to this ambitious low cost mission.

ISRU↗
DOE OSTI2018

Grazing-Angle Neutron Diffraction Study of the Water Distribution in Membrane Hemifusion: From the Lamellar to Rhombohedral Phase

The water distribution between lipid bilayers is important in understanding the role of the hydration force at different steps of the membrane fusion pathway. Here in this study, we used grazing-angle neutron diffraction to map out the water distribution in lipid bilayers transiting from a lamellar structure to the hemifusion “stalk” structure in a rhombohedral phase. Under osmotic pressure exerted by different levels of relative humidity, the lipid membrane sample was maintained in equilibrium at different lattices suitable for neutron diffraction. The D 2 O used to hydrate the lipid membrane sample stood out from the lipid in the reconstructed structure because of its much higher coherent neutron scattering length density. The density map indicates that water dissociated from the headgroup in the lamellar phase. In the rhombohedral phase, water was significantly reduced and was squeezed into pockets around the stalk. This study complements earlier structural studies by grazing-angle X-ray diffraction, which is sensitive to only the parts of the structure with high electron density (such as phosphors). The experiment also demonstrated that the recently developed time-of-flight small-angle neutron scattering beamline at the Spallation Neutron Source is suitable for grazing-angle neutron diffraction to provide the structures of large unit cells on the order of a few nanometers, such as biomembrane structures.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

Review of current neutron detection systems for emergency response

Neutron detectors are utilized in a myriad of applications—from safeguarding special nuclear materials (SNM) to determining lattice spacing in soft materials. The transformational changes taking place in neutron detection and imaging techniques in the last few years are largely being driven by the global shortage of helium-3 ( 3 He). This article reviews the status of neutron sensors used specifically for SNM detection in radiological emergency response. These neutron detectors must be highly efficient, be rugged, have fast electronics to measure neutron multiplicity, and be capable of measuring direction of the neutron sources and possibly image them with high spatial resolution. Neutron detection is an indirect physical process: neutrons react with nuclei in materials to initiate the release of one or more charged particles that produce electric signals that can be processed by the detection system. Therefore, neutron detection requires conversion materials as active elements of the detection system; these materials may include boron-10 ( 10 B), lithium-6 ( 6 Li), and gadollinium-157 ( 157 Gd), to name a few, but the number of materials available for neutron detection is limited. However, in recent years, pulse-shape-discriminating plastic scintillators, scintillators made of helium-4 ( 4 He) under high pressure, pillar and trench semiconductor diodes, and exotic semiconductor neutron detectors made from uranium oxide and other materials have widely expanded the parameter space in neutron detection methodology. In this article we will pay special attention to semiconductor-based neutron sensors. Finally, modern microfabricated nanotubes covered inside with neutron converter materials and with very high aspect ratios for better charge transport will be discussed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Performance Characterization of FB-Line Neutron Multiplicity Counter and Large Neutron Multiplicity Counter

Savanah River National Laboratory’s (SRNL) Nuclear Measurements group was tasked with characterizing the performance of two neutron multiplicity counters located at SRNL. Characterization measurements were made to determine the gate width, pre-delay, deadtime parameters, triples and doubles gate fractions, detector efficiency, and operating high voltage for the Large Neutron Multiplicity Counter (LNMC) and the FB Line Neutron Multiplicity Counter (FBLNMC). The parameters were determined, shown below, and were, as to be expected, slightly different than the previous calibrations, which were performed over 20 years ago. Several Pu samples were measured to validate the characterizations of the FBLNMC and LNMC. The measurements determined the sample Pu-240 mass within <2% deviation for the pure plutonium samples and ~8% for the mixed oxide sample. The pure Pu samples had significantly better accuracy compared with the impure mixed oxide sample due to the lack of induced fission or alpha,n neutrons from impurities. Overall, the characterization of the neutron multiplicity counters, and the determination of their operability has been completed successfully.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

Comparative assessment of different aluminum alloys for neutron beam window applications

The choice of an aluminum alloy window along a neutron beam requires careful consideration depending on the requirements of the instrument end station. The windows should generally be thin to minimize loss of neutrons from the beam due to scattering and absorption but still thick enough to be structurally sound for safety requirements. Further, the microstructure of the material is dependent on the alloy and the preparation method and may introduce scattering artifacts or smearing of the instrument resolution that are not desirable. In this manuscript, SANS and total cross section measurements of several different aluminum alloys will be presented and compared in order to provide some useful insight to engineers working on future neutron instrument design.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗