The neutron flux is a crucial factor for neutron scattering measurements, especially for compact sources. Among various neutron optics, grazing‐incidence focusing mirrors have been developed to give ...a significant increase in the neutron flux on a sample owing to their great potential for collecting neutrons in small‐angle neutron scattering (SANS) instruments. Focusing mirrors with a supermirror coating can be nested to collect a neutron beam with large divergence. Nested conical integrated assembly technology is employed to manufacture nested focusing mirrors. This study describes the design of ten‐shell nested fully annular quasi‐ellipsoidal focusing mirrors with an m = 3 Ni/Ti supermirror coating to produce enough neutrons on a sample under the premise of satisfying the specified minimum wavevector transfer Q. For fully annular focusing mirrors, the neutron current received by a sample from the entire annular focusing neutron beam is more relevant. A ray‐tracing method and current gain calculation are used to evaluate the performance of the designed mirrors. The ray‐tracing result shows that the ideal resolution of quasi‐ellipsoidal mirrors with four‐segment conical approximation is 1.354 mm. As the source radius decreases from 20 mm, the neutron current with the designed focusing mirrors can be enhanced by a factor of 13 to over 100 compared with that without focusing mirrors in the same detected area. The effective collecting area is 186 cm2 when the source radius is the optimal 15 mm. An 83‐fold current gain can be obtained for cold neutrons. The proposed mirrors can reach 90.7 and 87.3% of the maximum current of the corresponding optimal mirror structure when the source radii are 10 and 20 mm, respectively. The results demonstrate that the proposed mirrors are adaptable for instruments with changeable sources.
This study describes ten‐shell nested fully annular quasi‐ellipsoidal focusing mirrors with an m = 3 Ni/Ti supermirror coating for small‐angle neutron scattering. The proposed mirrors have been developed to gain enough neutrons on a sample for the specified minimum wavevector transfer Q and the results demonstrate adaptability for instruments with changeable sources.
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The extended Q‐range small‐angle neutron scattering diffractometer (EQ‐SANS) at the Spallation Neutron Source (SNS), Oak Ridge, is designed for wide neutron momentum transfer (Q) coverage, high ...neutron beam intensity and good wavelength resolution. In addition, the design and construction of the instrument aim to achieve a maximum signal‐to‐noise ratio by minimizing the background. The instrument is located on the high‐power target station at the SNS. One of the key components in the primary flight path is the neutron optics, consisting of a curved multichannel beam bender and sections of straight neutron guides. They are optimized to minimize neutron transport loss, thereby maximizing the available flux on the sample. They also enable the avoidance of a direct line of sight to the neutron moderator at downstream locations. The instrument has three bandwidth‐limiting choppers. They allow a novel frame‐skipping operation, which enables the EQ‐SANS diffractometer to achieve a dynamic Q range equivalent to that of a similar machine on a 20 Hz source. The two‐dimensional low‐angle detector, based on 3He tube technologies, offers very high counting rates and counting efficiency. Initial operations have shown that the instrument has achieved its design goals.
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In recent years, neutron radiography and tomography have been applied at different beam lines at Los Alamos Neutron Science Center (LANSCE), covering a very wide neutron energy range. The field of ...energy-resolved neutron imaging with epi-thermal neutrons, utilizing neutron absorption resonances for contrast as well as quantitative density measurements, was pioneered at the Target 1 (Lujan center), Flight Path 5 beam line and continues to be refined. Applications include: imaging of metallic and ceramic nuclear fuels, fission gas measurements, tomography of fossils and studies of dopants in scintillators. The technique provides the ability to characterize materials opaque to thermal neutrons and to utilize neutron resonance analysis codes to quantify isotopes to within 0.1 atom %. The latter also allows measuring fuel enrichment levels or the pressure of fission gas remotely. More recently, the cold neutron spectrum at the ASTERIX beam line, also located at Target 1, was used to demonstrate phase contrast imaging with pulsed neutrons. This extends the capabilities for imaging of thin and transparent materials at LANSCE. In contrast, high-energy neutron imaging at LANSCE, using unmoderated fast spallation neutrons from Target 4 Weapons Neutron Research (WNR) facility has been developed for applications in imaging of dense, thick objects. Using fast (ns), time-of-flight imaging, enables testing and developing imaging at specific, selected MeV neutron energies. The 4FP-60R beam line has been reconfigured with increased shielding and new, larger collimation dedicated to fast neutron imaging. The exploration of ways in which pulsed neutron beams and the time-of-flight method can provide additional benefits is continuing. We will describe the facilities and instruments, present application examples and recent results of all these efforts at LANSCE.
Chemistry and physics have made major advances in recent years, yielding much more complex systems with high hierarchical order across multiple length scales. Accordingly, characterization tools are ...required that can elucidate the structure of such new materials over all length scales. Simultaneous small‐angle neutron scattering (SANS) and ultra‐small‐angle neutron scattering (USANS) measurements are a unique tool to study such complexity and can be applied to very different fields of science. The OPUS (Option USANS) project is the study of a USANS option for SANS instruments, designed to be very versatile and easy to implement. The main idea is to provide the opportunity to study at the same time, and under the same experimental conditions, complex systems such as polymers, bio‐systems, complex fibres and self‐assembling systems. More specifically, this work presents the design of an option that could be applied to the suite of SANS instruments at the European Spallation Source (ESS) which will allow exploration of a Q range with a minimum Q down to one order of magnitude lower than the value attainable with the standard SANS instrument at the ESS. The proposed setup, based on the SAMBA (small‐angle multi‐beam analysis) approach, is very easy and fast to implement on a conventional SANS instrument and constitutes a multi‐beam approach involving two multi‐slits and a set of lenses near the sample position. This contribution describes all the focusing elements necessary to attain the proposed configuration and a detailed study using McStas simulations to optimize all the parameters involved for two SANS instruments: the future LoKI at the ESS and the present D11 at the Institut Laue–Langevin, the latter used as a benchmark for the model. Simulations performed without taking into account gravity effects show that the multi‐beam approach allows extending the Q ranges to 9 × 10−5–7 × 10−4 Å−1 and 5 × 10−5–3 × 10−4 Å−1 for LoKI and D11, respectively.
There is a rapidly growing trend in the application of ultra‐small‐angle neutron scattering (USANS) across many different fields of research, as a stand‐alone technique and in combination with small‐angle neutron scattering (SANS). Implementation of USANS capability on pin‐hole SANS instruments was investigated using neutron ray‐tracing simulations, and the design and optimization of the USANS optics are presented.
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Neutron grating interferometry is an advanced method in neutron imaging that allows the simultaneous recording of the transmission, the differential phase and the dark‐field image. The latter in ...particular has recently been the subject of much interest because of its unique contrast mechanism which marks ultra‐small‐angle neutron scattering within the sample. Hence, in neutron grating interferometry, an imaging contrast is generated by scattering of neutrons off micrometre‐sized inhomogeneities. Although the scatterer cannot be resolved, it leads to a measurable local decoherence of the beam. Here, a report is given on the design considerations, principles and applications of a new neutron grating interferometer which has recently been implemented at the ANTARES beamline at the Heinz Maier‐Leibnitz Zentrum. Its highly flexible design allows users to perform experiments such as directional and quantitative dark‐field imaging which provide spatially resolved information on the anisotropy and shape of the microstructure of the sample. A comprehensive overview of the neutron grating interferometer principle is given, followed by theoretical considerations to optimize the setup performance for different applications. Furthermore, an extensive characterization of the setup is presented and its abilities are demonstrated using selected case studies: (i) dark‐field imaging for material differentiation, (ii) directional dark‐field imaging to mark and quantify micrometre anisotropies within the sample, and (iii) quantitative dark‐field imaging, providing additional size information on the sample's microstructure by probing its autocorrelation function.
In this paper the principles, design and applications of the new neutron grating interferometry (nGI) setup at the Heinz Maier‐Leibnitz Zentrum are presented. The dark‐field contrast modality of the setup allows one to obtain spatially resolved information about the microstructure of a sample. In this way, nGI closes the gap between neutron imaging and small‐angle neutron scattering.
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Purpose:
Secondary neutrons are an unavoidable consequence of proton therapy. While the neutron dose is low compared to the primary proton dose, its presence and contribution to the patient dose is ...nonetheless important. The most detailed information on neutrons includes an evaluation of the neutron spectrum. However, the vast majority of the literature that has reported secondary neutron spectra in proton therapy is based on computational methods rather than measurements. This is largely due to the inherent limitations in the majority of neutron detectors, which are either not suitable for spectral measurements or have limited response at energies greater than 20 MeV. Therefore, the primary objective of the present study was to measure a secondary neutron spectrum from a proton therapy beam using a spectrometer that is sensitive to neutron energies over the entire neutron energy spectrum.
Methods:
The authors measured the secondary neutron spectrum from a 250‐MeV passively scattered proton beam in air at a distance of 100 cm laterally from isocenter using an extended‐range Bonner sphere (ERBS) measurement system. Ambient dose equivalent H*(10) was calculated using measured fluence and fluence‐to‐ambient dose equivalent conversion coefficients.
Results:
The neutron fluence spectrum had a high‐energy direct neutron peak, an evaporation peak, a thermal peak, and an intermediate energy continuum between the thermal and evaporation peaks. The H*(10) was dominated by the neutrons in the evaporation peak because of both their high abundance and the large quality conversion coefficients in that energy interval. The H*(10) 100 cm laterally from isocenter was 1.6 mSv per proton Gy (to isocenter). Approximately 35% of the dose equivalent was from neutrons with energies ≥20 MeV.
Conclusions:
The authors measured a neutron spectrum for external neutrons generated by a 250‐MeV proton beam using an ERBS measurement system that was sensitive to neutrons over the entire energy range being measured, i.e., thermal to 250 MeV. The authors used the neutron fluence spectrum to demonstrate experimentally the contribution of neutrons with different energies to the total dose equivalent and in particular the contribution of high‐energy neutrons (≥20 MeV). These are valuable reference data that can be directly compared with Monte Carlo and experimental data in the literature.
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Since the advent of the nuclear reactor, thermal neutron scattering has proved a valuable tool for studying many properties of solids and liquids, and research workers are active in the field at ...reactor centres and universities throughout the world. This classic text provides the basic quantum theory of thermal neutron scattering and applies the concepts to scattering by crystals, liquids and magnetic systems. Other topics discussed are the relation of the scattering to correlation functions in the scattering system, the dynamical theory of scattering and polarisation analysis. No previous knowledge of the theory of thermal neutron scattering is assumed, but basic knowledge of quantum mechanics and solid state physics is required. The book is intended for experimenters rather than theoreticians, and the discussion is kept as informal as possible. A number of examples, with worked solutions, are included as an aid to the understanding of the text.
The neutron instruments suite, installed at the spallation neutron source of the Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex (J-PARC), is ...reviewed. MLF has 23 neutron beam ports and 21 instruments are in operation for user programs or are under commissioning. A unique and challenging instrumental suite in MLF has been realized via combination of a high-performance neutron source, optimized for neutron scattering, and unique instruments using cutting-edge technologies. All instruments are/will serve in world-leading investigations in a broad range of fields, from fundamental physics to industrial applications. In this review, overviews, characteristic features, and typical applications of the individual instruments are mentioned.
The Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex (J-PARC) is a landmark large user-facility producing neutron and muon beams. Those beams ...feed over 20 beamlines hosting world-class instruments for the investigation of matter across the disciplines of materials science, solid state physics and chemistry, biological and life sciences, geology, engineering, and their wider applications. Neutron and muons can probe matter in very peculiar ways. They are sensitive to magnetism and hydrogen atoms, can penetrate materials deeply or probe surfaces, and allow one to investigate the fundamental dynamics of the materials. In the past three to four decades, neutron scattering has largely contributed to the development of modern technology, such as computers, mobile phone technology, electo-chemistry, the transportation industry, and the pharmaceutic industry. MLF is a world leader in such characterization technology and serves yearly to about 700 research experiments conducted from users of 34 countries around the world. The present book describes technical details of the proton accelerator, the neutron spallation source, the muon facility, and all the beamlines with engineering realization, specifications, and relevant examples.
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