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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Polyethylene density uncertainty in the simulation of neutron detectors

Simulations with the Monte Carlo N-Particle® (MCNP®) code are frequently used to study neutron coincidence counters for international safeguards. Reducing sources of uncertainty enables more accurate simulations, which reduces the need for expensive or impossible measurements. Accurately specifying the density of polyethylene is crucial for accurate simulations. The density of polyethylene ranges from 0.88 to 0.97 g/cm 3 and high-density polyethylene (HDPE) ranges from about 0.944 to 0.965 g/cm 3 . The density of a specific detector should be measured exactly for the best simulations. Here, the density of the blue/white Active Well Coincidence Counter (AWCC) bulk polyethylene was measured to be 0.9594 +- 0.0013 g/cm 3 at 1-sigma confidence. The density was calculated from repeated measurements of the various polyethylene dimensions for volume, and weighing the polyethylene for the mass. The AWCC neutron detection efficiency was simulated for each polyethylene density. The relative range of efficiencies (3σ) was 3.4% for unspecified polyethylene, 0.9% for HDPE, and 0.3% for the measured density. The impact of modeling small features such as screws was also studied and was found to be a negligible 0.2%. Measuring polyethylene density can reduce its role in uncertainty from one of the largest to one of the smallest contributors.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Impact of Spontaneous Fission Neutron Emission Energy on Neutron Detector Response

A parametric study was simulated in MCNP to investigate the impact of spontaneous fission neutron energy on neutron detector response. A total of 880 configurations were simulated by varying 3 He pressure and polyethylene reflector thickness for 8 different isotopes. Results showed that deviations between the simulated isotopes become more prevalent at higher energies with 238 U showing the greatest deviation. It was also observed that configurations comparable to most detection setups, 10 atm and 6 - 8 cm polyethylene, were closer to the upper bound of deviations from a 252 Cf. 240 Pu, a common spontaneous fission source of interest, ranged from 2% - 3% within this space. This suggests that further investigation is required to determine exact correction factors when calibrating neutron detectors with a 252 Cf. Although demonstrated here for a 4π-detection system, future plans include simulating a more detailed model of the MC-15 detection setup to determine exact correction factors for future experiments.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Critical and Californium Source-Driven Noise Analysis Subcritical Measurements with an Unreflected Cylindrical Tank of Mixed Uranium-Plutonium Nitrate Solution

The reported experiments were performed by Oak Ridge National Laboratory (ORNL) at the Battelle Northwest Laboratory’s (now Pacific Northwest National Laboratory) critical experiments facility at Hanford, Washington in 1981 and used 16 days of critical facility time, not including 10 days for setup and removal of ORNL equipment. These measurements were to assess the capability of the Cf source-driven noise analysis (CSDNA) method to measure the subcriticality (keff) of mixed U-Pu nitrate solutions. In addition to the CSNDA measurements, measurements were also performed near delayed criticality where CSDNA measurements cannot be performed. This report documents the experiments that were not reported at that time by presenting the ORNL experimental results and any online analysis performed during and shortly after the measurements. The mixed nitrate solution had a U concentration at 188 grams per liter (g/L), a Pu concentration of 280 g/L, free acid normality of 2.80, H ion molarity of 5.9 and a specific gravity of 1.754 g/cm 3 , a 240 Pu isotopic content of 7.981 wt. %, and a 235 U isotopic content of 0.724 wt. %. The stainless-steel tank for the solution had an inside diameter of 35.38 cm, an outside diameter of 35.53 cm, a height of 56.72 cm, and bottom thickness of 0.9525 cm. A Zircaloy pipe with a 3.1496 cm outside diameter, a 2.7788 cm inside diameter, and bottom thickness of 0.635 cm was available for insertion of the Cf source in the center of the fissile solution. The Cf source was also located at the outside surface of the tank (solution height varied from 10 to 53 cm) and in the center of the solution (solution height varied from 10 to 60.7 cm). The CSDNA measurements were not analyzed online to determine the subcritical neutron multiplication factors. At all subcritical states, the break frequency noise analysis data was fitted to obtain the prompt neutron decay constant. The neutron multiplication factors were determined for the two configurations of the measurements near delayed criticality. The subcritical neutron multiplication factors from the CNSDA measurements can be obtained with further analysis. However, the near delayed critical configuration, the prompt neutron decay constants, the count rates, and the measured cross and auto power spectral densities can be calculated directly for benchmarking. Much of data presented in this report are from ORNL notes—not in the ORNL logbooks. For the final benchmark analysis, the data from the Battelle Northwest Laboratory (which operated the critical facility in 1981) critical facility logbook should be consulted and be incorporated where appropriate. The purpose of this report is to document the experimental information for the measurements performed so that at a later date researchers could perform the required uncertainty and calculational analyses and documentation to use these data for an International Criticality Safety Benchmark Program (ICSBEP) or Nuclear Energy Agency benchmark. The data from these measurements are available from the ORNL Records Management Services Department, and the logbook is available from ICSBEP at Idaho National Laboratory. Preparation of the present report is part of a larger cooperative effort between Idaho National Laboratory (INL) and Oak Ridge National Laboratory (ORNL) to document more than 15 undocumented critical and subcritical experiments enumerated in ORNL/TM-2019/18 and performed by ORNL at ORCEF and other USDOE critical experiments facilities using more than 500 operational days of critical facility time.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Characterization of Impure Plutonium Oxide Neutron Calibration Standards through Evaluation by Neutron Multiplicity Equations

Plutonium oxide calibration standards STD4C, STD6C and STD8C have been historically used, and are currently the only MT52 standards in use, for calibration and measurement control program of Passive/Active Neutron Coincidence Counter known as PAN1 at PF-4. In this paper, previously measured high-statistics data are used in conjunction with neutron multiplicity equations to determine multiplication M and α parameter of these standards as the explicit knowledge of these parameters may allow quantification of precision and bias of accountability measurements of different material types and matrices of items.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2024

233 U oxide Measurement Campaign Data: Passive and Active Neutron Multiplicity Measurements of Uranium Oxide Samples at Oak Ridge National Laboratory

During FY2023, three measurement campaigns were conducted at Oak Ridge National Laboratory. The goal was to quantify the neutron signatures of samples of uranium oxide containing uranium 233 and uranium-235. This report presents the neutron multiplicity data obtained using the large volume active well coincidence counter (LV-AWCC).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1985

Some characteristics of the solar flare event of February 16, 1984

In the morning of February 16, 1984 a solar cosmic ray event (GLE) was recorded by the world wide network of neutron monitors (NM). The counting rate vs. time profile of the Goose Bay NM (geog. lat. = 53.3 deg. N, deog. long. = 299.6 deg E) where the increase is expressed as percent of the counting rate of an equatorial sea level NM is presented. The Goose Bay NM was observed to have the maximum response to the solar particles. Its counting rate vs. time profile exhibits a rapid increase to maximum, has a large amplitude (approx. 170%) and decays rapidly to background in approx. 90 min. In Fig. 1 we also show the counting rate vs. time profile for the Tixie Bay NM (71.6 deg, 128.9 deg) which recorded an increase of only a few percent. Since the NMs at Goose Bay and Tixie Bay have asymptotic viewing directions approx. 180 deg apart in longitude, the anisotropy of the solar particle flux at Earth from these stations.

Debrunner, H.↗
NASA NTRS2020

The Soft State of the Black Hole Transient Source MAXI J1820+070: Emission from the Edge of the Plunge Region?

The Galactic black hole X-ray binary MAXI J1820+070 had a bright outburst in 2018 when it became the second brightest X-ray source in the sky. It was too bright for X-ray CCD instruments such as XMM–Newton and Chandra, but was well observed by photon counting instruments such as Neutron star Inner Composition Explorer (NICER) and Nuclear Spectroscopic Telescope Array (NuSTAR). We report here on the discovery of an excess emission component during the soft state. It is best modelled with a blackbody spectrum in addition to the regular disc emission, modelled as either diskbb or kerrbb. Its temperature varies from about 0.9 to 1.1 keV, which is about 30–80 per cent higher than the inner disc temperature of diskbb. Its flux varies between 4 and 12 per cent of the disc flux. Simulations of magnetized accretion discs have predicted the possibility of excess emission associated with a non-zero torque at the innermost stable circular orbit (ISCO) about the black hole, which, from other NuSTAR studies, lies at about 5 gravitational radii or about 60 km (for a black hole, mass is 8Msun). In this case, the emitting region at the ISCO has a width varying between 1.3 and 4.6 km and would encompass the start of the plunge region where matter begins to fall freely into the black hole.

A C Fabian↗
DOE OSTI2019

Experimental Evaluation of the Fast-Neutron Passive Collar (FNPC) Performance and Comparison with Scintillation Based Collars

This report describes a new method for the verification of fresh low enrichment uranium (LEU) fuel assemblies that can reduce International Atomic Energy Agency (IAEA) inspection time in the field and be completely independent of operator declared burnable poison content. The passive measurement makes unattended mode operation practical, and thus provides the potential for reducing inspector time in the field for future applications. The new simplified passive neutron measurement uses the 238 U spontaneous fission in LEU fresh fuel rods to self-interrogate the 235 U mass in the neighboring rods. The measured response increases linearly with the increase in the linear density (LD) of 235 U. The relatively high efficiency of the passive neutron detector (24%) provides good statistical precision (~ 2%) for the singles, doubles, and triples counting rates in the thermal-neutron mode. The three observables makes possible multiplicity analysis so that both the 235 U LD and the effective burnable poison content can be determined independent of the operator declarations. This closes the potential diversion path of miss-declaration the burnable poison content. This report presents the detector design, the as-built system, the detector parameter measurements, the calibration, and the assay uncertainty estimates. The calibration measurements were performed using the Los Alamos Laboratory mockup PWR fuel assembly. The measurements were made in both the fastneutron mode (with Cd/Gd metal liners) and the thermal-neutron mode (no Cd/Gd liners).

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1989

Prompt Gamma Activation Analysis (PGAA): Technique of choice for nondestructive bulk analysis of returned comet samples

Prompt gamma activation analysis (PGAA) is a well-developed analytical technique. The technique involves irradiation of samples in an external neutron beam from a nuclear reactor, with simultaneous counting of gamma rays produced in the sample by neutron capture. Capture of neutrons leads to excited nuclei which decay immediately with the emission of energetic gamma rays to the ground state. PGAA has several advantages over other techniques for the analysis of cometary materials: (1) It is nondestructive; (2) It can be used to determine abundances of a wide variety of elements, including most major and minor elements (Na, Mg, Al, Si, P, K, Ca, Ti, Cr, Mn, Fe, Co, Ni), volatiles (H, C, N, F, Cl, S), and some trace elements (those with high neutron capture cross sections, including B, Cd, Nd, Sm, and Gd); and (3) It is a true bulk analysis technique. Recent developments should improve the technique's sensitivity and accuracy considerably.

Lindstrom, David J.↗
DOE OSTI2021

Characterization of a boron-loaded deuterated liquid scintillator for fast and thermal neutron detection

The preparation and characterization of novel boron-loaded deuterated liquid scintillators (BLDLS) are presented for the first time to investigate the performance of a detector sensitive to both fast and thermal neutrons intended for future neutron spectroscopy measurements. Three deuterated toluene-based scintillation cocktails were produced, one without boron, one loaded with ortho-carborane (natural boron isotopic abundance), and one with 96 wt% 10B enriched ortho-carborane. General optical and material properties were analyzed to include the composition, density, index of refraction, photoluminescence emission spectra, and absorbance spectra in addition to the relative light yield, resolution, relative efficiency, and pulse-shape-discrimination performance for all three scintillators and a hydrogen-based EJ-309 scintillator to evaluate the effects of boron loading in comparison with a common commercially-available scintillator and feasibility for future neutron spectroscopy measurements. Finally, the detection of shielded neutron sources was explored to capitalize on the 10B thermal neutron capture reaction. The results showed loading the scintillators with boron deteriorated the PSD performance slightly compared to the unloaded deuterated scintillator and resulted in a relative light yield loss of 26% and 41% for the 10B enriched and natural boron BLDLS, respectively. Lastly, the BLDLS have a higher relative detection efficiency than the unloaded deuterated scintillator for shielded neutron sources, based on total count rate, a desirable characteristic for missions related to finding and characterizing illicitly-trafficked special nuclear material.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗
NASA NTRS2003

Preliminary Analysis of the Multisphere Neutron Spectrometer

Crews working on present-day jet aircraft are a large occupationally exposed group with a relatively high average effective dose from galactic cosmic radiation. Crews of future high-speed commercial aircraft flying at higher altitudes would be even more exposed. To help reduce the significant uncertainties in calculations of such exposures, the Atmospheric Ionizing Radiation (AIR) Project, an international collaboration of 15 laboratories, made simultaneous radiation measurements with 14 instruments on five flights of a NASA ER-2 high-altitude aircraft. The primary AIR instrument was a highly sensitive extended-energy multisphere neutron spectrometer with lead and steel shells placed within the moderators of two of its 14 detectors to enhance response at high energies. Detector responses were calculated for neutrons and charged hadrons at energies up to 100 GeV using MCNPX. Neutron spectra were unfolded from the measured count rates using the new MAXED code. We have measured the cosmic-ray neutron spectrum (thermal to greater than 10 GeV), total neutron fluence rate, and neutron effective dose and dose equivalent rates and their dependence on altitude and geomagnetic cutoff. The measured cosmic-ray neutron spectra have almost no thermal neutrons, a large "evaporation" peak near 1 MeV and a second broad peak near 100 MeV which contributes about 69% of the neutron effective dose. At high altitude, geomagnetic latitude has very little effect on the shape of the spectrum, but it is the dominant variable affecting neutron fluence rate, which was 8 times higher at the northernmost measurement location than it was at the southernmost. The shape of the spectrum varied only slightly with altitude from 21 km down to 12 km (56 - 201 grams per square centimeter atmospheric depth), but was significantly different on the ground. In all cases, ambient dose equivalent was greater than effective dose for cosmic-ray neutrons.

Goldhagen, P.↗
DOE OSTI2024

Optimization of ray-tracing simulations to confirm performance of the GP-SANS instrument at the High-Flux Isotope Reactor

The CG-2 beamline at the High Flux Isotope Reactor (HFIR) exhibits a notable discrepancy between observed count rates and the count rates we would expect based on a Monte-Carlo neutron ray-trace simulation. These simulations consistently predict count rates approximately five times greater than those observed in four separate experimental runs involving different instrument configurations. This discrepancy suggests that certain factors are causing losses in measurements that are not adequately accounted for in the simulation, in particular guide reflectivity or misalignment. To investigate these discrepancies, a high-dimensional simulation parameter approach is applied in order to understand the losses. Region of Interest (ROI) groups along the instrument are assigned to different surfaces of the guide components within the simulation. This allows the parameters of those guide components to be varied as a group to minimize the complexity of the search space. The result is an optimization of simulation parameters using an iterative scheme that aims to minimize the difference between experimentally measured count rates and simulated count rates across all tested collimator combinations. This proposed methodology holds the potential to reveal previously unrecognized sources of intensity loss in the CG-2 beamline at HFIR and improve the accuracy of simulations, leading to enhanced understanding and performance of the beamline for various scientific applications.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2022

The development of a 6 Li-based pixelated neutron detector for neutron reflectometry at the Spallation Neutron Source

We present a high-rate 6 Li-based pixelated neutron detector developed for neutron reflectometry instruments at the Spallation Neutron Source (SNS). The neutron detector has a pixelated design: each 6 Li scintillator element has its own photosensor and independent channel readout. This paper focuses on the general overview of the detector design and construction, the characterization of the pixelated detector, and the results of the first neutron reflectivity experiments conducted using the pixelated neutron detector at the SNS Liquid Reflectometer (BL-4B). The pixelated neutron detector demonstrated a global time-average count rate of ≥ 1.8 x 10 6 cps, at least 3 orders of magnitude higher than that of the existing neutron detector ( 3 He-based Multi-Wire Proportional Counter), and a local instantaneous count rate of ≥ 1.73 x 10 6 cps / cm 2 . The maximum counting rate of the detector has not yet been determined as the detector is capable of handling the maximum flux available at the beamline. Furthermore, the outcome of the neutron reflectivity experiments showed that the pixelated neutron detector is a promising candidate for next-generation neutron reflectometry instruments at the SNS.

6Li, silicon photomultiplier↗
NASA NTRS1975

Comparisons of ground-based monitor data with Pioneers 8, 9, 10 and 11 observations in 1968-1974

The paper examines ground-based neutron monitor data and the counting rates in different energy channels on the Pioneer 8, 9, 10 and 11 spacecraft to determine the scale size of the transient cosmic-ray variations (Forbush decreases) and the relationship of these variations to changes in the interplanetary magnetic field. Since the Pioneer spacecraft sampled the inner modulating region extensively, the spatial extent of Forbush decreases (Fd's) can be determined. In some cases the Fd modulating region was co-rotating and in others radially expanding. The azimuthal extent of the Fd region was variable but was typically about 45 deg in extent. These observations will be interpreted in terms of models proposed for Fds.

Lockwood, J. A.↗
NASA NTRS1973

Upper limit to the 1-20 MeV solar neutron flux.

The upper limit on the quiet time solar neutron flux from 1 to 20 MeV has been measured to be less than .002 neutrons at the 95% confidence level. This result is deduced from the OGO-6 neutron detector measurements of the 'day-night' effect near the equator at low altitudes for the period from June 7 to Dec. 23, 1969. The OGO-6 detector had very low (less than 4%) counting rate contributions from locally produced neutrons in the detecting system and the spacecraft and from charged-particle interactions in the neutron sensor.

Lockwood, J. A.↗
DOE OSTI2026

Rapid neutron and gamma-ray source localization using machine learning

Rapid localization of radiation sources is critical for applications including nuclear emergency response, safeguards, and security. However, conventional imaging systems such as neutron scatter cameras and Compton cameras depend on rare coincidence events, which often result in long acquisition times. In this work, we address the challenge of rapid source localization by developing a machine learning approach to predict the direction of a single radiation source using only count rates from an array of neutron and gamma-ray detectors. The proposed model is a fully connected neural network (FCNN) trained using Monte Carlo simulation data from a 252 Cf source. The model hyperparameters are optimized with a small set of routine 252 Cf measurements. We benchmarked the performance of the trained and optimized machine learning model using additional 252 Cf , 137 Cs , and PuBe measurements under laboratory conditions with varying source-detector configurations. For these measurements, the machine learning model achieved a mean localization error smaller than 30° with 3 x 10 3 system counts, corresponding to 8 s measurement time for the imaging system used in this work. In this low-statistics regime, the method outperformed traditional scatter-based imaging by more than 75% in localization accuracy for the evaluated measurement configurations. These results demonstrate that a machine learning-based approach can significantly reduce the time required for accurate single-source localization, providing a robust and computationally efficient alternative to traditional imaging systems in time-critical nuclear security and emergency response scenarios.

Gamma-ray imaging↗