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At least 937 records · Page 52

Crystallographic texture gradient along the wall thickness of an SF-copper tube

Metallic tubes usually show heterogeneities along circumference and through wall thickness. Local texture analysis by synchrotron diffraction and global texture analysis by neutron diffraction was used describing texture variations related to the wall thickness. Test sample was an SF-Cu tube with outer diameter of 140 mm and an average wall thickness of 10 mm. The texture is dominated by the cube component {001} <100>. Other minor components are rotated cube {013} <100>, Goss {011} <100>, Cu {112} <111>, brass {110} <112>, S {123} <634>. The texture gradient over the wall thickness shows a remarkable variation of the sharpness of the cube component. Other components show only little variation. Comparing samples obtained at maximum wall thickness and at minimum wall thickness one can see that the wall thickness has an influence on the global texture as well as texture gradient. Another interesting result is, that global textures measured directly by neutrons and averaged global textures, calculated from the set of local measurements by synchrotron diffraction, agree surprisingly well despite their different resolution.

36 MATERIALS SCIENCE↗

Demonstration of two-dimensional time-encoded imaging of fast neutrons

Here, we present a neutron detector system based on time-encoded imaging, and demonstrate its applicability toward the spatial mapping of special nuclear material. We also demonstrate that two-dimensional fast-neutron imaging with 2° resolution at 2 m stand-off is feasible with only two instrumented detectors.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

LANL Efforts on Neutron Coincidence Modeling of INL Pulsed Neutron Data [Slides]

Overview of this presentation is: (1) pulsed histogram analysis, (2) creation of SPNS, (3) use of SPNS for modeling pulsed neutron data, (4) creation of MUDI, (5) calculated accidentals correction using GUAM + MUDI, (6) background subtraction analysis, and (7) current/figure work with MCNP.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Minding the Gap

Neutron & X-ray scattering provides nano- to meso-scale details of complex fluid structure; 1D electronic density maps dervied from SAXS yield molecular level insights; Neutron reflectivity provides substructure details of substrate supported complex fluids; Complex fluids composition can be optimized to support a wide variety of both soluble and membrane proteins; The water gap dimensions can be finely tuned through polymer component.

Material Science↗

Elimination of ghosting artifacts from wavelength-shifting fiber neutron detectors

Misassignment of neutron position (ghosting) produces artifacts, which have been observed in wavelength-shifting (WLS) fiber detectors developed for time-of-flight (TOF) neutron powder diffraction. In position-sensitive detectors (PSDs) with WLS fiber encoding, thermal and cold neutrons interact with a monolithic 6LiF/ZnS:Ag scintillator screen, and scintillation photons are generated and transported through the crossed fibers to photomultipliers (PMTs). The neutron position is determined by photon counts in PMTs within a preset time window. Ghosting occurs when neutrons hit the group boundaries of two neighboring PMTs for x-position multiplexing, which is modeled as resulting from a long travel length (about 3-5 mm) of a small number of scintillation photons. This model is supported by the change observed in aperture images when the threshold number for photon-pulses was adjusted for a neutron event determination. When the threshold number of photon-pulses was set above 10 for each PMT, the ghost peaks in the aperture images and TOF spectra of powder diffraction were strongly suppressed or completely eliminated, and the intrinsic background levels of the WLS detectors were significantly reduced. Our result indicates that WLS fiber detector is a promising alternative for 3He PSDs for neutron scattering.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Neutron temporal diagnostic for high-yield deuterium–tritium cryogenic implosions on OMEGA

A next-generation neutron temporal diagnostic (NTD) capable of recording high-quality data for the highest anticipated yield cryogenic deuterium–tritium (DT) implosion experiments was recently installed at the Omega Laser Facility. A high-quality measurement of the neutron production width is required to determine the hot-spot pressure achieved in inertial confinement fusion experiments—a key metric in assessing the quality of these implosions. The design of this NTD is based on a fast-rise-time plastic scintillator, which converts the neutron kinetic energy to 350- to 450-nm-wavelength light. The light from the scintillator inside the nose-cone assembly is relayed ∼16 m to a streak camera in a well-shielded location. An ∼200× reduction in neutron background was observed during the first high-yield DT cryogenic implosions compared to the current NTD installation on OMEGA. An impulse response of ∼40 ± 10 ps was measured in a dedicated experiment using hard x-rays from a planar target irradiated with a 10-ps short pulse from the OMEGA EP laser. The measured instrument response includes contributions from the scintillator rise time, optical relay, and streak camera.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

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 ↗

Single-Volume Neutron Scatter Camera for High-Efficiency Neutron Imaging and Spectroscopy

Neutron detection provides an effective method to detect, locate, and characterize sources of interest to nuclear security applications. Current neutron imaging systems based on double-scatter kinematic reconstruction provide good signal vs. background discrimination and spectral capability, but suffer from poor sensitivity due to geometrical constraints. This weakness can be overcome if both neutron-proton scattering interactions are detected and resolved within one large contiguous active detector volume. We describe here a maximum likelihood approach to event reconstruction in a single-volume system with no optical segmentation and sensitivity to individual optical photons on the surfaces of the scintillator. We present results from a Geant4-based simulation establishing the feasibility of this single-volume neutron scatter camera concept given notional performance of existing photodetector and readout technologies.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

A New Era of Discovery: The 2023 Long Range Plan for Nuclear Science

Nuclear science is the investigation of how protons and neutrons are formed from elementary particles and how the forces between those particles produce both nuclei and the vast variety of nuclear phenomena that occur in the universe. It has evolved into a broad field that addresses profound scientific questions: Where does the mass of visible matter come from? How do stars ignite, live, and die? How do nuclei illuminate the search for new laws of nature? This science points the way to using nuclei to build new technologies that benefit society.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Thermal Gradient and Neutron Irradiation Experiment Design for Fusion Reactor Materials in the Advanced Test Reactor

This work outlines a hypothetical coupled thermal gradient and neutron irradiation experiment in the Advanced Test Reactor (ATR) at the Idaho National Laboratory. Although the ATR is a thermal spectrum test reactor and doesn’t inherently produce a flux spectrum dominated by the high-energy neutrons typical in a fusion reactor, it’s multitude of experiment positions and dynamic flux environment make it a suitable platform for investigating fusion related issues.

36 MATERIALS SCIENCE↗

Neutron Damage and MAX Phase Ternary Compounds

The Demands of Gen IV nuclear power plants for long service life under neutron radiation at high temperature are severe. Advanced materials that would withstand high temperatures (up to 1000+ C) to high doses in a neutron field would be ideal for reactor internal structures and would add to the long service life and reliability of the reactors. The objective of this work is to investigate the response of a new class of machinable, conductive, layered, ternary transition metal carbides and nitrides - the so-called MAX phases - to low and moderate neutron dose levels.

36 MATERIALS SCIENCE↗

High-sensitivity fast neutron detector KNK-2-7M

The construction of the fast neutron detector KNK-2-7M is briefly described. The results of the study of the detector in the pulse-counting mode are given for the fissions of {sup 237}Np nuclei in the radiator of the neutron-sensitive section and in the current mode with the separation of sectional currents of functional sections. The possibilities of determining the effective number of {sup 237}Np nuclei in the radiator of the neutronsensitive section are considered. The diagnostic possibilities of the detector in the counting mode are shown by example of the analysis of the reference data from the neutron-field characteristics in the working hall of the BR-K1 reactor. The diagnostic possibilities of the detector in the current operating mode are shown by example of the results of measuring the {sup 237}Np-fission intensity in the BR-K1 reactor power start-ups implemented in the mode of fission-pulse generation on delayed neutrons at the detector arrangement inside the reactor core cavity under conditions of a wide variation of the reactor radiation field.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

Neutron Irradiation Experiments

This presentation discusses the ongoing and upcoming neutron irradiation experiments within the Advanced Materials and Manufacturing Technologies (AMMT) program for the 2024 AMMT program review meeting. Ongoing and upcoming neutron irradiation of additively manufactured 316 stainless steel and A709 in the High Flux Isotope Reactor and Advanced Test Reactor are described.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

Fast multiplicity counter featuring stilbene detectors for special nuclear material assay

The Treaty on the Nonproliferation of Nuclear Weapons demands for new instruments to prevent diversion of fissile material and safeguard controls. We present a fast neutron multiplicity counting system based on organic scintillators, i.e. liquid EJ-309 and stilbene. The system is able to detect fission correlated counts and photon and neutron multiplets, needed to quantify fissile mass, without the need of complex electronic circuitry and unfolding procedures, required in moderated systems. Moderated system, typically based on helium-3 detectors, feature a gate time of hundreds of microseconds. Conversely, the use of organic scintillators allows an exceptionally short gate time of hundreds of nanoseconds. This results in a reduction of accidental neutron coincidence. In our system, the superior gamma-neutron discrimination capabilities of stilbene scintillators allow to measure high-order multiplicities (> 3) and the inspection of complex source terms. This counter is thus also suitable for the assay of newer fuels containing plutonium and other fissionable actinides. A prototypal version of the well-counter was assembled and tested at the University of Michigan, using a spontaneous fission and an (a,n) neutron source, i.e. 252Cf and PuBe respectively. Presented measured results show excellent agreement with simulations. The viability of the system to discriminate time-correlated fission neutrons from random, uncorrelated neutrons was proved. An experimental campaign will be carried out at Idaho National Laboratory in August 2015 to characterize weapon grade plutonium samples.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Status Report on the Passive Neutron Enrichment Meter (PNEM) for UF 6 Cylinder Assay

The Passive Neutron Enrichment Meter (PNEM) is a nondestructive assay (NDA) system being developed at Los Alamos National Laboratory (LANL). It was designed to determine 235 U mass and enrichment of uranium hexafluoride (UF 6 ) in product, feed, and tails cylinders (i.e., 30B and 48Y cylinders). These cylinders are found in the nuclear fuel cycle at uranium conversion, enrichment, and fuel fabrication facilities. The PNEM is a 3 He-based neutron detection system that consists of two briefcase-sized detector pods. A photograph of the system during characterization at LANL is shown in Fig. 1.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

Neutron Instruments for Research in Coordination Chemistry

Here, neutron diffraction and spectroscopies offer unique insight into structures and properties of solids and molecular materials. All neutron instruments located at the various neutron sources are distinct, even if their designs are based on similar principles, and thus, are usually less familiar to the community than commercial X–ray diffractometers and optical spectrometers. Major neutron instruments in the USA, which are open to scientists around the world, and examples of their use in coordination chemistry research are presented here, along with a list of similar instruments at main neutron facilities in other countries. The reader may easily and quickly find from this mini–review an appropriate neutron instrument for research. The instruments include single–crystal and powder diffractometers to determine structures, inelastic neutron scattering (INS) spectrometers to probe magnetic and vibrational excitations, and quasielastic neutron scattering (QENS) spectrometers to study molecular dynamics such as methyl rotation on ligands. Key and unique features of the diffraction and neutron spectroscopies that are relevant to inorganic chemistry are reviewed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗