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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Validating ENDF/B-VIII.1beta1 with LLNL Pulsed-Sphere Neutron-Leakage Spectra [Slides]

In this presentation 6 Li Distinct changes are observed. 235 U Discussion shows Improvements (seen in VIII.1beta0) are coming from new PFNS informed by Chi-Nu experimental data. Additionally, 239 Pu large changes coming from inelastic scattering. 9 Be ENDF/B-VIII.0 shows to be better right after elastic peak while 16 O had slight changes. 19 F had small improvements in ENDF/B-VIII.1 and 56 Fe had noticeable changes in thicker spheres. Examples of negligible changes for the sake of completeness are given.

16-Oxygen↗
DOE OSTI2023

Validating ENDF/B-VIII.1beta2 with LLNL Pulsed-Sphere Neutron-Leakage Spectra [Slides]

This presentation covers noteworthy changes from VIII.1beta0/1 to VIII.1beta2. 6 Li has been fixed (also seen in 7 Li sphere). For 9 Be: we would recommend studying what nuclear data led to an increase in C/E right after peak. For Pb isotopes: we are concerned about new structures introduced after peak. Finally discussed for 239 Pu: Is it worth improving right now?

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1997

Hard X-ray spectra of neutron stars and black hole candidates

The hard X-ray behavior of several X-ray binary systems containing a neutron star or a black hole candidate is analyzed in an attempt to determine the specific signature of these categories of compact objects. Limiting the consideration to two subclasses of neutron stars, Atoll sources and non-pulsating Z sources, it appears that only the Atoll sources have a spectral behavior similar to black holes. It is proposed that Atoll sources are weakly magnetized neutron stars, whereas Z sources are small radius moderate magnetized neutron stars. Large magnetic fields funnel the accreting matter, thus preventing spherical accretion and free fall if the neutron star radius is smaller than the last stable accreting orbit. Weak magnetic fields do not have this effect, and blackbody soft photons from the stellar surface are upscattered on the relativistic infalling matter, leading to excess hard X-rays. This excess is visible in two of the observed Atoll sources and in the spectrum of a black hole candidate. In the case of a Z source, a lack of photons was remarked, providing a possible signature to distinguish between these classes of objects.

Durouchoux, P.↗
DOE OSTI2014

WE-D-17A-05: Measurement of Stray Radiation Within An Active Scanning Proton Therapy Facility: EURADOS WG9 Intercomparison Exercise of Active Dosimetry Systems

Purpose: Intercomparison of active dosemeters in the measurement of stray radiation at the Trento active-scanning proton therapy facility. Methods: EURADOS WG9 carried out a large intercomparison exercise to test different dosemeters while measuring secondary neutrons within a 230 MeV scanned proton therapy facility. Detectors included two Bonner Sphere Spectrometers (BSS), three tissue equivalent proportional counters (TEPCHawk) and six rem-counters (Wendi II, Berthold, RadEye, a regular and an extended-range Anderson and Braun NM2B counters). Measurements of neutron ambient dose equivalents, H*(10), were done at several positions inside (8 positions) and outside (3 positions) the treatment room while irradiating a water tank phantom with a 10 × 10 × 10 cc field. Results: A generally good agreement on H*(10) values was observed for the tested detectors. At distance of 2.25 m and angles 45°, 90° and 180° with respect to the beam axis, BSS and proportional counters agreed within 30%. Higher differences (up to 60%) were observed at the closest and farthest distances, i.e. at positions where detectors sensitivity, energy, fluence and angular response are highly dependent on neutron spectra (flux and energy). The highest neutron H*(10) value, ∼60 microSv/Gy, was measured at 1.15 m along the beam axis. H*(10) decreased significantly with the distance from the isocenter dropping to 1.1 microSv/Gy at 4.25 m and 90° from beam axis, ∼2 nanoSv/Gy at the entrance of the maze, 0.2 nanoSv/Gy at the door outside the room and below detection limit in the gantry control room and at an adjacent room. These values remain considerately lower than those of passively scattered proton beams. BSS and Hawk unfolded spectra provide valuable inputs when studying the response of each detector. Conclusion: TEPCs and BSS enable accurate measurements of stray neutrons while other rem-meters also give satisfactory results but require further improvements to reduce uncertainties.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2014

Neutron dosimetry in solid water phantom

The neutron spectra, the Kerma and the absorbed dose due to neutrons were estimated along the incoming beam in a solid water phantom. Calculations were carried out with the MCNP5 code, where the bunker, the phantom and the model of the15 MV LINAC head were modeled. As the incoming beam goes into the phantom the neutron spectrum is modified and the dosimetric values are reduced.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2015

Measurement of stray radiation within a scanning proton therapy facility: EURADOS WG9 intercomparison exercise of active dosimetry systems

Purpose: To characterize stray radiation around the target volume in scanning proton therapy and study the performance of active neutron monitors. Methods: Working Group 9 of the European Radiation Dosimetry Group (EURADOS WG9—Radiation protection in medicine) carried out a large measurement campaign at the Trento Centro di Protonterapia (Trento, Italy) in order to determine the neutron spectra near the patient using two extended-range Bonner sphere spectrometry (BSS) systems. In addition, the work focused on acknowledging the performance of different commercial active dosimetry systems when measuring neutron ambient dose equivalents, H{sup ∗}(10), at several positions inside (8 positions) and outside (3 positions) the treatment room. Detectors included three TEPCs—tissue equivalent proportional counters (Hawk type from Far West Technology, Inc.) and six rem-counters (WENDI-II, LB 6411, RadEye™ NL, a regular and an extended-range NM2B). Meanwhile, the photon component of stray radiation was deduced from the low-lineal energy transfer part of TEPC spectra or measured using a Thermo Scientific™ FH-40G survey meter. Experiments involved a water tank phantom (60 × 30 × 30 cm{sup 3}) representing the patient that was uniformly irradiated using a 3 mm spot diameter proton pencil beam with 10 cm modulation width, 19.95 cm distal beam range, and 10 × 10 cm{sup 2} field size. Results: Neutron spectrometry around the target volume showed two main components at the thermal and fast energy ranges. The study also revealed the large dependence of the energy distribution of neutrons, and consequently of out-of-field doses, on the primary beam direction (directional emission of intranuclear cascade neutrons) and energy (spectral composition of secondary neutrons). In addition, neutron mapping within the facility was conducted and showed the highest H{sup ∗}(10) value of ∼51 μSv Gy{sup −1}; this was measured at 1.15 m along the beam axis. H{sup ∗}(10) values significantly decreased with distance and angular position with respect to beam axis falling below 2 nSv Gy{sup −1} at the entrance of the maze, at the door outside the room and below detection limit in the gantry control room, and at an adjacent room (<0.1 nSv Gy{sup −1}). Finally, the agreement on H{sup ∗}(10) values between all detectors showed a direct dependence on neutron spectra at the measurement position. While conventional rem-counters (LB 6411, RadEye™ NL, NM2-458) underestimated the H{sup ∗}(10) by up to a factor of 4, Hawk TEPCs and the WENDI-II range-extended detector were found to have good performance (within 20%) even at the highest neutron fluence and energy range. Meanwhile, secondary photon dose equivalents were found to be up to five times lower than neutrons; remaining nonetheless of concern to the patient. Conclusions: Extended-range BSS, TEPCs, and the WENDI-II enable accurate measurements of stray neutrons while other rem-counters are not appropriate considering the high-energy range of neutrons involved in proton therapy.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2014

Forward fitting of experimental data from a NE213 neutron detector installed with the magnetic proton recoil upgraded spectrometer at JET

In this paper, we present the results obtained from the data analysis of neutron spectra measured with a NE213 liquid scintillator at JET. We calculated the neutron response matrix of the instrument combining MCNPX simulations, a generic proton light output function measured with another detector and the fit of data from ohmic pulses. For the analysis, we selected a set of pulses with neutral beam injection heating (NBI) only and we applied a forward fitting procedure of modeled spectral components to extract the fraction of thermal neutron emission. The results showed the same trend of the ones obtained with the dedicated spectrometer TOFOR, even though the values from the NE213 analysis were systematically higher. This discrepancy is probably due to the different lines of sight of the two spectrometers (tangential for the NE213, vertical for TOFOR). The uncertainties on the thermal fraction estimates were from 4 to 7 times higher than the ones from the TOFOR analysis.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Multiphysics approach to plasma neutron source modelling at the JET tokamak

A novel multiphysics methodology for the computation of realistic plasma neutron sources has been developed. The approach is based on state-of-the-art plasma transport and neutron spectrum calculations, coupled with a Monte Carlo neutron transport code, bridging the gap between plasma physics and neutronics. In the paper two JET neutronics tokamak models are used to show the application of the developed plasma neutron sources and validate them. Diagnostic data for the record JET D discharge 92436 are used as input for the TRANSP code, modelling neutron emission in two external plasma heating scenarios, namely using only neutral beam injection and a combination of the latter and ion cyclotron resonance heating. Neutron spectra, based on plasma transport results, are computed using the DRESS code. The developed PLANET code package is employed to generate plasma neutron source descriptions and couple them with the MCNP code. The effects of using the developed sources in neutron transport calculations on the response of JET neutron diagnostic systems is studied and compared to the results obtained with a generic plasma neutron source. It is shown that, although there are significant differences in the emissivity profiles, spectra shape and anisotropy between the neutron sources, the integral response of the time-resolved ex-vessel neutron detectors is largely insensitive to source changes, with major relative deviations of up to several percent. However it is calculated that, because of the broadening of neutron spectra as a consequence of external plasma heating, larger differences may occur in activation of materials which have threshold reactions located at DD neutron peak energies. The PLANET plasma neutron source computational methodology is demonstrated to be suitable for detailed neutron source effect studies on JET during DT experiments and can be applied to ITER analyses.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Upgrades of Diagnostic Techniques and Technologies for JET next D-T Campaigns

JET next D-T campaign is presently scheduled for the year 2017. The main scientific objectives include the assessment of the isotopic effects on various plasma aspects: mainly on confinement, on the threshold to access the H mode and on ELM behaviour. From a technical point of view, the total yield of the entire D-T phase is expected to be 1.7 1021 neutrons, about a factor of six higher than the previous main D-T campaign on JET, DTE1. Therefore the radiation field will be quite relevant for next step devices, since the neutron flux at the first wall (∼10{sup 16} n/cm{sup 2}s), for example, will be comparable to the one in ITER behind the blanket. From a point of view of diagnostics developments, for many years JET diagnostics have been upgraded in order to provide adequate support for the scientific exploitation of a D-T campaign. The main efforts have concentrated on improving three main aspects of JET measuring capability: 1) the quality of the measurements of the electron and ion fluids to support the plasma physics programme 2) the diagnostic for the fusion products 3) diagnostic technologies for ITER. In terms of general diagnostic capability, compared to the previous DTE1, JET diagnostics have a much better spatial and temporal resolution of both the ion and electron fluid (about one order of magnitude improvement for each parameter). The consistency of the various independent measurements of the same parameters has also increased significantly; the three independent measurements of the electron temperature, for example, agree now within 5%. Moreover, solutions are being addressed to operate some cameras, both visible and IR, even during the full D-T phase to provide imaging of the plasma and the first wall. Various upgrades of neutral particle analysis are being considered, mainly to measure the isotopic composition. A new set of reflectometers is expected to provide valuable information about the changes in the turbulence with the different fuel mixtures. With regard to the fusion products, JET now can deploy a consistent set of techniques to measure the neutron yield and neutron spectra and to diagnose the fast particles. A full calibration of the neutron diagnostics with a 14 MeV source is being considered, after the recent very successful calibration for the 2.45 MeV neutrons. Vertical and horizontal lines of sight are foreseen for neutron and gamma spectrometry, in order to better determine the thermal neutron yield and to separate the trapped and passing components of the alphas. Various gamma ray spectrometers are being developed to cover all the various operational scenarios, from trace tritium to 50-50 D-T operation. The redistribution of the alphas will be measured with the gamma ray cameras, recently upgraded with full digital electronics; new detectors are being considered to bring the time resolution of the system in the ten of ms range. The lost alphas will also be diagnosed with improved spatial and temporal resolution, using Faraday cups and a scintillator probe. From a technological perspective, the D-T campaign will provide a unique opportunity to test ITER relevant technologies. From radiation hard detectors, for example Hall probes, to neutron absorbers and to shielding concepts, the potential of various solutions in a realistic 14 MeV radiation field will be assessed. The effects of neutrons and gamma on ancillary technologies and systems, such as fibre optics and electronics circuits, are also expected to be sufficiently high to derive useful information about the competitive advantage of various alternatives.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Synthesizing pseudo-Kossel lines from neutron transmission data. I. An analytical approach for recovering single-crystal orientation

The energy-dispersive neutron spectra transmitted through single crystals are characterized by sharp Bragg dips at specific wavelengths, where Bragg's law is being fulfilled for certain crystallographic planes. This phenomenon allows for developing methods for crystal-orientation determination techniques similar to electron backscatter diffraction and X-ray diffraction microscopy. This work presents a new procedure to recover the orientation matrix for single crystals using transmission spectra recorded during rotation of a crystal about an axis perpendicular to a polychromatic neutron beam. The proposed method consists of an initial transformation of the as-collected wavelength–rotation maps to a wavevector $\textit{K}$ space, resulting in linear pseudo-Kossel lines that are suitable for analysis and indexing using image-processing procedures. Further, simulated neutron transmission spectra through a copper crystal with known orientations were used to set and prove the numerical approach. This technique may be expanded for cases where the neutron beam intersects multiple single-crystal grains with different orientations.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Predicting Activation of Experiments Inside the Annular Core Research Reactor

The objective of this thesis is to create a program to quickly estimate the radioactivity and decay of experiments conducted inside of the Annular Core Research Reactor at Sandia National Laboratories and eliminate the need for users to write code. This is achieved by model the neutron fluxes in the reactor’s central cavity where experiments are conducted for 4 different neutron spectra using MCNP. The desired neutron spectrum, experiment material composition, and reactor power level are then input into CINDER2008 burnup code to obtain activation and decay information for every isotope generated. DREAD creates all of the files required for CINDER2008 through user selected inputs in a graphical user interface and executes the program for the user and displays the resulting estimation for dose rate at various distances. The DREAD program was validated by weighing and measuring various experiments in the different spectra and then collecting dose rate information after they were irradiated and comparing it to the dose rates that DREAD predicted. The program provides results with an average of 17% higher estimates than the actual values and takes seconds to execute.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2015

A new method to reduce the statistical and systematic uncertainty of chance coincidence backgrounds measured with waveform digitizers

We present a new method for measuring chance-coincidence backgrounds during the collection of coincidence data. The method relies on acquiring data with near-zero dead time, which is now realistic due to the increasing deployment of flash electronic-digitizer (waveform digitizer) techniques. An experiment designed to use this new method is capable of acquiring more coincidence data, and a much reduced statistical fluctuation of the measured background. A statistical analysis is presented, and us ed to derive a figure of merit for the new method. Factors of four improvement over other analyses are realistic. The technique is illustrated with preliminary data taken as part of a program to make new measurements of the prompt fission neutron spectra at Los Alamo s Neutron Science Center. In conclusion, it is expected that the these measurements will occur in a regime where the maximum figure of merit will be exploited

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Conceptual Design of a Thermal–to-14-MeV Neutron Conversion Device for Use in the Advanced Test Reactor

Here, this paper details the conceptual design of a thermal-to-14-MeV neutron converter consisting of a mixture of lithium and deuterium in a blanket material. Such a device operates a two-step reaction, first generating tritons via thermal neutron absorption in the tritium breeding material, and in the second step, high-energy neutrons are produced either via deuterium-tritium fusion reaction or with tritium reacting with lithium. A thermal-to-14-MeV neutron converter significantly hardens the neutron spectrum by virtually removing thermal neutrons and adding a high-energy 14 MeV component to the neutron spectrum. While similar concepts have been previously proposed and tested in other reactors, the unique characteristics of the Advanced Test Reactor (ATR), namely its important thermal flux (up to $10^{15}$ n.cm$^{-2}$.s$^{-1}$) makes it markedly attractive for obtaining a very large fast neutron flux, usable for irradiation studies under neutron flux conditions prototypical of fusion reactors. The paper provides a description of a new computational scheme developed for handling the coupled neutron-triton transport mechanism using the Geant4 toolkit. Resulting neutron spectra and high-energy neutron yields are summarized for different irradiation positions and potential neutron breeder materials. Maximum predicted thermal-to-14-MeV neutron yields are on the order of $2.10^{-4}$, which is consistent with previous studies found in the literature. Thus, when placed inside the ATR, such a neutron converter will be providing the largest high-energy neutron source available for activation and irradiation studies of materials foreseen for use in fusion reactors. Future steps will involve qualifying the computational scheme using the ATR critical facility using activation foil measurements.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2023

Reactivity Coefficient Measurements to Aid in Reducing Compensating Errors in Plutonium Nuclear Data

Compensating errors between several nuclear data observables in a nuclear data library can adversely impact application simulations. The primary goal of the EUCLID project (Experiments Underpinned by Computational Learning for Improvements in Nuclear Data) is to reduce compensating errors between fast (0.1–5 MeV) 239Pu nuclear data for prompt fission neutron spectra (PFNS), average prompt fission neutron multiplicities, and neutron induced fission, capture, elastic, and inelastic cross sections. This work will focus on the design and execution of void reactivity coefficient measurements in the EUCLID experiment, performed on the Planet vertical lift critical assembly machine at the National Criticality Experiments Research Center (NCERC). Two different base configurations were designed and measured, one with high neutron leakage, and one with low neutron leakage. Both were primarily made up of plutonium metal (Zero Power Physics Reactor plates) without interstitial moderators and reflected by half-inch aluminum. Design optimization showed that void reactivity coefficient measurements in three locations per configuration was most impactful to reduce nuclear data uncertainties due to the varying impacts from elastic and inelastic scattering, as well as fission and capture. The locations for measurements were chosen based on preliminary studies which balanced measurement uncertainty and measurement practicality. The measurements were also selected to have sensitivities maximally complementary to previous arrangements. Comparisons across nuclear data libraries highlight the potential impact.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗