Use Of Neutrons Research Articles

Applications of nuclear techniques relevant for civil security

The list of materials which are subject to inspection with the aim of reducing the acts of terrorism includes explosives, narcotics, chemical weapons, hazardous chemicals and radioactive materials. To this we should add also illicit trafficking with human beings. The risk of nuclear terrorism carried out by sub-national groups is considered not only in construction and/or use of nuclear device, but also in possible radioactive contamination of large urban areas. Modern personnel, parcel, vehicle and cargo inspection systems are non-invasive imaging techniques based on the use of nuclear analytical techniques. The inspection systems use penetrating radiations: hard x-rays (300 keV or more) or gamma-rays from radioactive sources (137Cs and 60Co with energies from 600 to 1300 keV) that produce a high resolution radiograph of the load. Unfortunately, this information is ‘‘non-specific’’ in that it gives no information on the nature of objects that do not match the travel documents and are not recognized by a visual analysis of the radiographic picture. Moreover, there are regions of the container where x and gamma-ray systems are ‘‘blind’’ due to the high average atomic number of the objects irradiated that appear as black spots in the radiographic image. Contrary to that is the use of neutrons; as results of the bombardment, nuclear reactions occur and a variety of nuclear particles, gamma and x-ray radiation is emitted, specific for each element in the bombarded material. The problem of material (explosive, drugs, chemicals, etc.) identification can be reduced to the problem of measuring elemental concentrations. Neutron scanning technology offers capabilities far beyond those of conventional inspection systems. The unique automatic, material specific detection of terrorist threats can significantly increase the security at ports, border-crossing stations, airports, and even within the domestic transportation infrastructure of potential urban targets as well as protecting armed forces and infrastructure.

Use of neutron and synchrotron X-ray diffraction for evaluation of residual stresses in a 2024-T351 aluminum alloy variable-polarity plasma-arc weld

The residual stress fields associated with variable-polarity plasma-arc (VPPA) welds in 2024-T351 aluminum alloy plates have been measured nondestructively using neutron and synchrotron X-ray diffraction. Neutron diffraction allows in-depth measurements of the full strain tensor to be made in thick components; synchrotron X-rays allow for rapid measurements of strains inside components, although their penetration is less than that of the neutrons and constraints arising from the diffraction geometry generally lead to only two strain components being easily measurable. Hence, a combination of the two techniques, applied as described herein, is ideal for a detailed nondestructive evaluation of residual stresses in plates. The residual stresses in a 12-mm-thick VPPA-welded aluminum 2024-T351 alloy plate have been measured using neutron diffraction. The stresses were then remeasured by a combination of neutron and synchrotron X-ray diffraction after the plate had been reduced in thickness (or, skimmed) to 7 mm by machining both sides of the weld, mimicking the likely manufacturing operation, should such welds be used in aerospace structures. A strong tensile residual stress field was measured in the longitudinal direction, parallel to the weld, in both the as-welded and skimmed specimens. There was only a slight modification of the residual stress state on skimming.

Neutron and X-ray diffraction measurements on micro- and nano-sized precipitates embedded in a Ni-based superalloy and after their extraction from the alloy

Neutron and X-ray diffraction are eminently suitable techniques to determine lattice misfit in nickel-based superalloys. Due to the different measuring techniques and sensitivities of the probes, sometimes one method is preferable to the other. This paper demonstrates how the use of neutrons allows a better determination of the misfit value in a bulk single-crystal tungsten-rich nickel superalloy with oriented precipitates than the use of X-rays, although the resolution in neutron diffraction is generally inferior to that in X-ray diffraction. It also yields more accurate results when the precipitates are at the nanoscale. The neutron measurements were carried out using a special technique to detect a larger number of reflections in single-crystal samples than observed in standard diffraction geometry. A comparison of the measurements by neutron and X-ray diffraction of precipitates separated from the bulk is also included in the investigation.

The new Athens center on data processing from the neutron monitor network in real time

Abstract. The ground-based neutron monitors (NMs) record galactic and solar relativistic cosmic rays which can play a useful key role in space weather forecasting, as a result of their interaction with interplanetary disturbances. The Earth's-based neutron monitor network has been used in order to produce a real-time prediction of space weather phenomena. Therefore, the Athens Neutron Monitor Data Processing Center (ANMODAP) takes advantage of this unique multi-directional device to solve problems concerning the diagnosis and forecasting of space weather. At this moment there has been a multi-sided use of neutron monitors. On the one hand, a preliminary alert for ground level enhancements (GLEs) may be provided due to relativistic solar particles and can be registered around 20 to 30 min before the arrival of the main part of lower energy particles responsible for radiation hazard. To make a more reliable prognosis of these events, real time data from channels of lower energy particles and X-ray intensity from the GOES satellite are involved in the analysis. The other possibility is to search in real time for predictors of geomagnetic storms when they occur simultaneously with Forbush effects, using hourly, on-line accessible neutron monitor data from the worldwide network and applying a special method of processing. This chance of prognosis is only being elaborated and considered here as one of the possible uses of the Neutron Monitor Network for forecasting the arrival of interplanetary disturbance to the Earth. The achievements, the processes and the future results, are discussed in this work.

The use of neutron scattering in the study of ceramics

Neutron scattering is a versatile probe used to study the structure and dynamics of materials. It has particular relevance to the investigation of ceramics and has been used in their study since neutron scattering was first developed almost sixty years ago. This review will focus on the relative merits of neutron scattering compared to other microscopic probes, with particular reference to ceramic materials, and will illustrate the uses of neutron diffraction and inelastic neutron scattering in various key fields of ceramic research.

Non-destructive diagnostics of irradiated materials using neutron scattering from pulsed neutron sources

The advantage of neutron-scattering studies as compared to the standard X-ray technique is the high penetration of neutrons that allow us to study volume effects. The high resolution of instrumentation on the basis neutron scattering allows measurement of the parameters of lattice structure with high precision. We suggest the use of neutron scattering from pulsed neutron sources for analysis of materials irradiated with pulsed high current electron and ion beams. The results of preliminary tests using this method for Ni foils that have been studied by neutron diffraction at the IBR-2 (Pulsed Fast Reactor at Joint Institute for Nuclear Research) are presented.

The use of neutrons and monochromatic X-rays for non-destructive testing in geological materials

In the paper we present our results for element sensitive high-energy X-ray tomography and high-speed thermal neutron tomography applied to geological samples. The tuneable monochromatic X-ray beam was used for element sensitive tomography of geological samples containing heavy elements using the K-edge dichromatic scanning technique. This type of NDT (non-destructive testing) allowed us to reveal the quantity and location of uranium, lead and mercury in Oklo samples (natural nuclear reactor) and Cinnabar stones. Fast 3-D thermal neutron imaging of dynamical processes was successfully tested at the high flux neutron tomography station of the ILL. The qualitative investigation of water repellents and consolidants applied on sandstones of Bray and limestones of Maastricht were the first samples to be studied with the new imaging technique.

Rare earth hexaborides: large single crystals

Single crystals of the rare earth hexaborides have been grown successfully by the floating zone technique using a high-power Xenon arc Image furnace. Large, high-quality crystals up to 1 cc in volume have been obtained for several rare earth hexaborides by this method. Crystals of these compounds have also been grown using enriched 11 B isotope for use in neutron scattering studies. The crystal growth and characterisation of these crystals are reported in the paper.

Use of Neutron and Synchrotron X-ray Diffraction for Non-destructive Evaluation of Weld Residual Stresses in Aluminium Alloys

A full three-dimensional residual stress tensor was determined through a combination of neutron and synchrotron X-ray diffraction in a MIG welded Al2024 plate. The plate was first measured by synchrotron X-rays to determine the strain in the longitudinal (LD) and transverse directions (TD). Then the same plate was measured by pulsed neutrons for the transverse and normal strain directions. The stress-free lattice reference (d 0) across the weld was obtained by measuring a comb sample of insufficient constraint to hold an internal residual stress field. The point-to-point corrected strain data of the three principal directions obtained was then combined to calculate the full three-dimensional residual stress tensor. The comparability of the processes was confirmed by comparing the strain observed in the transverse direction. The combination of these two different experiments enabled determination of a full through-thickness stress map across the weld.

New Frontiers in the Application of Neutron Scattering to Materials Science

AbstractThis brief article describes the content of the December 2003 issue of MRS Bulletin on New Frontiers in the Application of Neutron Scattering to Materials Science. New techniques, new instrumentation, and new sources are providing exciting opportunities for the use of neutron scattering in materials research at a time when the pace of research and development is accelerating while the complexity of the issues governing materials use is increasing. At a time such as this, it is critical to use the best tool for the job, and neutron scattering is evolving into a tool that can be used with many others, rather than a technique only for the specialist. It is also providing unprecedented resolution in energy to allow the study of the slow dynamics characteristic of many problems in soft matter and to probe surfaces and interfaces in a unique way. In this issue, we have chosen three areas to emphasize these trends: neutron reflectivity as a probe of surfaces and interfaces, the use of neutrons to study complex fluids, and high-resolution neutron scattering studies of dynamics. We also give a view of the future of neutron sources, with an article outlining the opportunities to be provided by sources proposed or under construction in Europe, Japan, and the United States. It is our hope that this sampling of new opportunities in neutron scattering will encourage wider use of these techniques to help solve the challenging materials research problems of today and tomorrow.

FaME38: A New Approach to Materials Science at the ILL-ESRF

The Facility for Materials Engineering (FaME38) was inaugurated on the joint ILL-ESRF site in November 2002 to encourage and to support the use of neutrons and synchrotron X-rays for materials engineering research. FaME38 actively encourages new engi

Neutron activation analysis and provenance research in archaeology

Neutron activation analysis is a powerful quantitative analytical technique withapplication in a broad range of disciplines such as agriculture, archaeology,geochemistry, health and human nutrition, environmental monitoring andsemiconductor technology. Due to its excellent sensitivity, great accuracy andprecision, and versatility, the technique is a suitable method for analysing manydifferent types of samples. Archaeologists, in particular, have made extensive useof neutron activation analysis for the purpose of characterizing archaeologicalmaterials and determining their provenance. This paper presents a briefhistory of the technique and its application to archaeology, describes thephysics behind the analytical method, and explains how the method isgenerally employed to determine the sources of archaeological materials.

Growth of large single crystals of rare earth hexaborides

Single crystal growth of several rare earth hexaborides has been carried out by the floating zone technique. A high-power xenon arc lamp image furnace was used for the crystal growth. Large high-quality crystals of LaB 6, CeB 6, PrB 6 and NdB 6, about 1 cm 3 in volume have been obtained. Crystals of all these compounds have also been grown using enriched 11 B isotope for use in neutron scattering experiments.

Development of Drabkin energy filters for JSNS project

We have a plan to install Drabkin energy filters for neutron spectrometers at the Japanese Spallation Neutron Source (JSNS) project. Combined with a high-intensity coupled moderator, a Drabkin energy filter could be very useful to obtain a high-resolution polarized beam with higher intensity than a beam from a decoupled moderator. Hence, it could bring about a breakthrough for more efficient use of neutrons at neutron spectrometers. We have developed a Drabkin energy filter which has 10 periods of spatially oscillating magnetic field and measured spin–flip probabilities as functions of field strength and of neutron wavelength. In this paper, results of the performance tests of Drabkin energy filters are presented and discussed.

Effective pair interatomic potential and self-diffusion of molten tin

The interatomic potential and the structures of liquids are important to predict the diffusion coefficient. The effective pair interatomic potential of liquid tin was evaluated by the inverse scheme from experimental static structure factors, which were obtained by the use of neutron and X-ray scattering experiments at temperatures up to 1873 K. The interatomic potential obtained was applied to the molecular dynamics simulation and the diffusion coefficient of liquid tin was evaluated. The self-diffusion coefficient obtained was, even in the sense of temperature dependence, in good agreement with the experimental data, which were obtained with no convection under low gravity.

An introduction to the use of neutron scattering methods in mineral sciences

We review the current state of the field of neutron scattering as applied to studies of mineral behaviour. Neutron scat- tering is a particularly versatile tool because it is able to measure both structure (diffraction) and dynamics (spectroscopy) of mate- rials at an atomic level, and because it is able to measure both coherent and incoherent scattering processes. As a result, there is a wide range of phenomena that can be studied using neutron scattering. The versatility of the tool is shown to arise within a gen- eral theoretical framework. Applications of neutron scattering in the Earth and Mineral Sciences are described.

Present status and perspectives on neutron scattering instrumentation development at IPNS

Since its beginnings in ZING-P in the early 1970s, the Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory has played an important role in the development of neutron scattering instrumentation, particularly in the utilization of time-of-flight techniques such as time-focusing for diffractometers. IPNS operates a user program for 11 instruments 25 weeks per year with a call for proposals every 6 months. As a medium-flux user facility, it serves the needs of the broader scientific community while providing training in the design and use of neutron scattering instruments for the next generation of scientists. The instruments at IPNS are continually being upgraded and evaluated; a significantly improved quasielastic neutron spectrometer was commissioned in 2000, and a similar enhancement on the high-resolution, medium-energy-range chopper spectrometer is currently underway. An enhancement plan, which includes improvements to most of the instruments and would approximately double the scientific throughput of IPNS, was recently reviewed and highly recommended. IPNS has lead responsibility for neutron scattering instruments for the Spallation Neutron Source being built at Oak Ridge National Laboratory and has played a leading role in developing a proposal for target station and instruments for a long wavelength target station submitted in January 2001 to the National Science Foundation. Through these and other projects, IPNS will continue to be a source and testbed for novel neutron scattering instrumentation concepts. Thus, IPNS will play a vital role in the global neutron scattering community for the foreseeable future.

Investigations of zeolitic materials at the NIST Center for Neutron Research

Crystallographic studies of four zeolitic materials using neutron powder diffraction data are presented. In most cases, these projects benefited from the combined use of neutron and x-ray measurements.

The recent development of neutronic techniques for determination of residual stresses

Neutron diffraction is a well-established non-destructive method for the measurement of residual stress deep inside materials. This paper gives a short overview of the use of neutrons for materials research and measurement techniques. Neutron diffraction has been applied in determining residual stresses in metal matrix composites. Measurement and prediction of residual stress for plastic deformation are presented. More recently, the neutron diffraction technique has also been applied for the determination of plastic strain which results from microstructural defects and leads to peak broadening. Influence of the shot penning treatment on austenitic steel is presented.

Magnetic scattering experiments

We discuss the relative use of neutrons and X-rays as scattering tools to probe the magnetic properties of materials. Neutron diffraction experiments continue to be the most appropriate tool to determine the magnetic structure of bulk solids. Synchrotron X-ray experiments are and will be used to investigate selectively the magnetic behaviour of different chemical species and/or electronic shells in magnetic systems. There exist some grey areas where the two probes can be used depending on the scientific problem under investigation. In particular, neutrons allow very accurate measurements of magnetic form factors, but X-rays provide a separation of the orbital momentum contribution to magnetisation. Comparisons between X-rays and neutrons studies of magnetism at surfaces are presented. Finally, one can anticipate that only inelastic neutron scattering experiments will allow the observation of magnetic excitations across the whole Brillouin zone.