Directional neutron spectrometer.
Directional neutron spectrometer for events in which neutron is scattered by first scintillator into second
NEUTRON SPECTROMETRY↗
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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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Development of a compact fast-neutron spectrometer for nuclear emergency response applications
We have developed a Compact Fast Neutron Spectrometer (CFNS) for passive assay of special nuclear material (SNM) through the observation of fast neutrons. The CFNS consists of eight organic glass scintillators (OGS) coupled to silicon photomultipliers and a waveform digitizer, which are integrated within a human-portable box. The CFNS determines the neutron energy profile by spectrum unfolding using the Maximum-Likelihood Expectation Maximization method. The detector acquisition system was optimized to have a dynamic range of up to 10 MeV neutron energy. Bulk special nuclear material (SNM) measurements from the National Criticality Experiments Research Center were analyzed for SNM validation/examination. Additionally, the results show that the CFNS can be used to distinguish between fission and (α, n) neutron emitters, regardless of intervening material type (Cu and polyethylene) and thickness, by taking the ratio of neutron counts at different regions in the unfolded energy spectrum. Additionally, by fitting an exponential curve to the unfolded energy spectrum of PuO 2 and Pu neutron emitters, the CFNS showed the ability of distinguishing between pure Pu oxide, pure Pu metal and mixed oxide-metal configurations.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Quantification of the light output anistropy in deuterated stilbene
Deuterated stilbene is an organic scintillator that is a desirable material for fast neutron spectroscopy using spectrum unfolding techniques without requiring time-of-flight information. Due to the crystal structure of the material, some anisotropy of the light output exists, which is dependent on the direction of heavy charged particle recoil relative to the crystal structure. The anisotropy of trans-stilbene (hereafter referred to as stilbene) has been well characterized in previous work, but for deuterated stilbene, the anisotropy has only been partially characterized along the a and b crystal axes, while the artificial c' axis, which shows the largest anisotropy in stilbene, has not been characterized until this publication. Here, in this work, two deuterated stilbene crystals were characterized with neutron energies up to 35 MeV at the Los Alamos Neutron Science Center. For one of the crystals, the response is characterized along the a, b, and c' axes. This characterization shows a distinct anisotropy along the axes in deuterated stilbene, which is very similar to that found in regular stilbene, such that the a axis is the brightest, while the b' and c' axes are approximately 3% and 20%–35% lower relative to the a axis.
36 MATERIALS SCIENCE↗
Measurement of muon-induced neutron yield at the China Jinping Underground Laboratory *
Abstract Solar, terrestrial, and supernova neutrino experiments are subject to muon-induced radioactive background. The China Jinping Underground Laboratory (CJPL), with its unique advantage of a 2400 m rock coverage and long distance from nuclear power plants, is ideal for MeV-scale neutrino experiments. Using a 1-ton prototype detector of the Jinping Neutrino Experiment (JNE), we detected 343 high-energy cosmic-ray muons and (7.86 3.97) muon-induced neutrons from an 820.28-day dataset at the first phase of CJPL (CJPL-I). Based on the muon-induced neutrons, we measured the corresponding muon-induced neutron yield in a liquid scintillator to be μ −1 g −1 cm 2 at an average muon energy of 340 GeV. We provided the first study for such neutron background at CJPL. A global fit including this measurement shows a power-law coefficient of (0.75 0.02) for the dependence of the neutron yield at the liquid scintillator on muon energy.
Zhao, Lin↗
Neutron detection efficiency of the Neutron dEtector with Xn Tracking (NEXT)
An efficient neutron detection system with good energy resolution is required to correctly characterize decays of neutron-rich nuclei where β-delayed neutron emission is a dominant decay mode. The Neutron dEtector with Xn Tracking (NEXT) has been designed to measure β-delayed neutron emitters. By segmenting the detector along the neutron flight path, NEXT reduces the associated uncertainties in neutron time-of-flight measurements, improving energy resolution while maintaining detection efficiency. Detector prototypes are comprised of optically separated segments of a neutron-gamma discriminating plastic scintillator coupled to position-sensitive photomultiplier tubes. In this work we discuss how the first performance studies of this detector showed that high intrinsic neutron detection efficiency could be achieved while retaining good energy resolution. The results from the efficiency measurements using neutrons from direct reactions are presented
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Thermonuclear neutron emission from a sheared-flow stabilized Z-pinch
We report the fusion Z-pinch experiment (FuZE) is a sheared-flow stabilized Z-pinch designed to study the effects of flow stabilization on deuterium plasmas with densities and temperatures high enough to drive nuclear fusion reactions. Results from FuZE show high pinch currents and neutron emission durations thousands of times longer than instability growth times. While these results are consistent with thermonuclear neutron emission, energetically resolved neutron measurements are a stronger constraint on the origin of the fusion production. This stems from the strong anisotropy in energy created in beam-target fusion, compared to the relatively isotropic emission in thermonuclear fusion. In dense Z-pinch plasmas, a potential and undesirable cause of beam-target fusion reactions is the presence of fast-growing, “sausage” instabilities. This work introduces a new method for characterizing beam instabilities by recording individual neutron interactions in plastic scintillator detectors positioned at two different angles around the device chamber. Histograms of the pulse-integral spectra from the two locations are compared using detailed Monte Carlo simulations. These models infer the deuteron beam energy based on differences in the measured neutron spectra at the two angles, thereby discriminating beam-target from thermonuclear production. An analysis of neutron emission profiles from FuZE precludes the presence of deuteron beams with energies greater than 4.65 keV with a statistical uncertainty of 4.15 keV and a systematic uncertainty of 0.53 keV. This analysis demonstrates that axial, beam-target fusion reactions are not the dominant source of neutron emission from FuZE. These data are promising for scaling FuZE up to fusion reactor conditions.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Measurement of proton quenching in a plastic scintillator detector
The non-linear energy response of the plastic scintillator EJ-260 is measured with the MicroCHANDLER detector, using neutron beams of energy 5 to 27 MeV at the Triangle Universities Nuclear Laboratory. The first and second order Birks' constants are extracted from the data, and found to be $k_B = (8.70 \pm 0.93)\times 10^{-3}\ {\rm g/cm^2/MeV}$ and $k_C = (1.42 \pm 1.00) \times 10^{-5}\ {\rm (g/cm^2/MeV)^2}$. This result covers a unique energy range that is of direct relevance for fast neutron backgrounds in reactor inverse beta decay detectors. Furthermore, these measurements will improve the energy non-linearity modeling of plastic scintillator detectors. In particular, the updated energy response model will lead to an improvement of fast neutron modeling for detectors based on the CHANDLER reactor neutrino detector technology.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Design and commissioning of the Correlated Gamma-Neutron Array for sCattering (CoGNAC)
The Correlated Gamma-Neutron Array for sCattering (CoGNAC) is a dual $n$-$γ$ detector array fielded at the Weapons Neutron Research facility at the Los Alamos Neutron Science Center. Here, the detector array utilizes elpasolite detectors and liquid scintillators to perform measurements of neutron elastic and inelastic scattering cross sections and emitted particle angular distributions. This manuscript details the design and experimental setup of CoGNAC as well as some of the preliminary studies performed to select the elpasolite detectors deployed in the array. Examples of the analysis methods available to CoGNAC are given in the context of past CoGNAC measurements of neutron scattering reactions on 28 Si and 56 Fe.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Cosmic and solar gamma ray and neutron experiments
This report summarizes the results of the research supported by NASA grant NAGW-2734 and lists the papers and publications produced through the grant. The basic goal of the work was to complete analysis of data from exposure of a large NaI scintillation detector to fast neutrons and to disseminate the results of the analysis. A secondary goal was to compare the measured detector response to neutrons with Monte Carlo calculations of the response. In Section 2.0, we discuss the goals of the research. In Section 3.0, we summarize the results of the research. In Section 4.0, we list the papers and publications produced under the grant. Preprints or reprints of the publications are attached as appendices.
Dunphy, Philip P.↗
Cosmic ray scintillations. III - The low-frequency limit and observations of interplanetary scintillations
Statistically significant broad-band fluctuations, or 'scintillations', in the high-energy (about 1 GeV) cosmic ray intensity observed by neutron monitors are interpreted. The scintillations are caused by fluctuations in the interplanetary magnetic field. The theory of the scintillations is presented for the low-frequency limit, below .0001 Hz, including the effects of the earth's rotation on the fluxes observed by the neutron monitors. The observations and the theory are in good agreement. The shapes and amplitudes of the observed spectra and, in particular, a broad enhancement in the power spectrum of the Deep River neutron monitor flux near 1 cpd are related to the interplanetary magnetic field power spectrum and the cosmic ray anisotropy.
Owens, A. J.↗
Neutron-gamma noise measurements in a zero-power reactor using organic scintillators
Not Available
22 GENERAL STUDIES OF NUCLEAR REACTORS↗
Boron-loaded organic glass scintillators
Herein we report the progress towards an organic glass scintillator with fast and thermal neutron sensitivity providing “triple” pulse shape discrimination (PSD) through the inclusion of a boron-incorporated aromatic molecule. Here, the commercially available molecule 2-(p-tolyl)-1,3,2-dioxaborinane (TDB) can be readily synthesized in one step using inexpensive materials and incorporated into the organic glass scintillator at 20% by weight or 0.25% 10 B by mass. In addition, we demonstrate that TDB can be easily scaled up and formulated into organic glass scintillator samples to produce a thermal neutron capture signal with a light yield equivalent to 120.4 ± 3.7 keVee, which is the highest value reported in the literature to date.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Design of a High-Speed Neutron Imager Using a Boron-Loaded Organic Glass Scintillator
Not provided.
Engineering↗
Rossi Alpha Measurements – Rapid Organic (n, $\gamma$) Discrimination Detector (RAM-RODD) system capabilities
The Rossi Alpha Measurements–Rapid Organic (n, $\gamma$) Discrimination Detector (RAM-RODD) is an array organic scintillation detectors that has been optimized for use in neutron noise measurements. This report details the capability of the system including the method of energy calibration, pulse shape discrimination, and time resolution.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Scintillators and Detectors for MeV X-ray and Neutron Imaging
Explore the source record for details and available documents.
Engineering - Instrumentation related to nuclear s↗
Measurements of temporally- and spatially-resolved neutron production in a sheared-flow stabilized Z-pinch
A novel approach using multiple scintillator detectors is applied to measure temporally- and spatially-resolved neutron production in the Fusion Z-pinch Experiment (FuZE) device, a Sheared-Flow Stabilized (SFS) Z-pinch. Diagnosing neutron production from FuZE is important for determining if fusion is thermonuclear and whether the FuZE device can be scaled toward reactor conditions. Absolute yields of up to 2 × 10 5 neutrons per discharge are measured with calibrated plastic scintillator detectors operating in pulse-counting mode. Neutron emission durations of up to ~8 μs are inferred by recording the time difference between the first and last pulses for each discharge. Multiple scintillator detectors located at different positions with respect to the fusing plasma are used to demonstrate that the axial extent of the neutron producing region is comparable to the device volume. Scintillator detectors are well-suited as neutron diagnostics for FuZE and other plasma devices with similar yields and emission durations. Increasing the neutron yield, duration, and volume of the neutron emitting region within the plasma column are significant experimental objectives for FuZE.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
LLE Diagnostic Resource Team for Innovative Fusion Concepts (Final Report)
The LLE Diagnostic Resource Team for Innovative Fusion Concepts provided travelling neutron diagnostics, consultancy on neutron diagnostics, and consultancy on tritium handling to fusion companies. An existing neutron detector was recalibrated for low yields and two detectors were built based on designs proven on the Omega Laser Facility. The three detectors allow measurements over a wide range of yields (from 10 to 1E7 incident neutrons). The detectors were calibrated for DD neutrons on a dedicated OMEGA shot day. Neutron detectors from the company MIFTI were also calibrated on OMEGA. MIFTI is currently using their detectors and two of our detectors on staged Z-pinch experiments at UCSD. The Team acted as consultants for the development of a liquid scintillator array to detect neutrons from muon induced fusion by NK Labs. Segments of NK Labs’ detector were tested at the LLE using radioactive sources and a DD neutron generator. The Team also acted as consultants for the design of a tritium handling system for NK Labs. A new type of neutron spectrometer was designed and built, and has completed preliminary testing.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Coated fiber optic chemical and radiation sensors
Distributed fiber optic chemical and radiation sensors formed by coating the fibers with certain types of response materials are provided. For distributed chemical sensors, the coatings are reactive with the targets; the heat absorbed or released during a reaction will cause a local temperature change on the fiber. For distributed radiation sensors, coating a fiber with a scintillator enhances sensitivity toward thermal neutrons, for example, by injecting light into the fiber. The luminescent components in these materials are taken from conjugated polymeric and oligomeric dyes, metal organic frameworks with sorbed dyes, and two-photon-absorbing semiconductors. The compositions may exhibit strong gamma rejection. Other scintillators combining luminescent materials with neutron converters are available. With a multiple-layer coating, it may be possible to identify the presence of both neutrons and gamma rays, for example. Coatings may be applied during manufacture or in the field.
Lamberti, Vincent E.↗