Neutron Guides Research Articles

New Ballistic Neutron Guide for the Time-of-Flight Spectrometer FOCUS at PSI

FOCUS is a direct-geometry cold neutron time-of-flight spectrometer at SINQ (PSI, CH). Its neutron guide was exchanged in 2019/2020 within the SINQ Upgrade project, while the rest of the instrument remained unchanged. The new guide provided a significant intensity increase across the whole spectrum, especially at short wavelengths, due to the more efficient transport and extended phase space of the transported neutrons. The practically available energy transfer range (at the neutron energy loss side) was increased to about 40 meV. The main reason for the intensity benefit at short incident wavelengths was the improved guide coating, whereas at long wavelengths it was the new ballistic shape. The interesting part of the guide is the “peanut shape” of the curved part in the horizontal plane. For this, we derived the analytical restriction on the geometry to avoid a direct line of sight from the source. The guide geometry and the supermirror coating were optimized using Mcoptimize, a particle swarm optimization routine employing Mcstas. Future ballistic neutron guides may profit from the presented approaches, optimization strategy, and results.

D11 and small angle neutron scattering: a paradigm of ILL

This paper describes some of the early events in the 50 year success of D11. That, and the Institut Laue Langevin are linked by an attitude that embraces both instrument renewal and new areas of science. The neutron sources proved to be reliable and serviceable, the neutron guides and guide hall have been a great benefit, and the user concept has led to a strengthening international community of diverse and good science and to new instruments clamouring for funding in a growing facility. Designs were perfected and the second wind (Deuxième Souffle) funded the outflow from which a second strong phase has evolved.Graphical

Endurance – Modernisation of the instrumentation suite at the Institut Laue-Langevin

Endurance encompasses more than 30 new or upgraded instrument and infrastructure projects, rolled out over 8 years between 2016 and 2023. Many new or upgraded instruments have already been deployed and are in user-operation including: the fission-fragment gamma ray spectrometer, FIPPS; the upgraded cold-neutron TOF spectrometer IN5; new thermal TOF spectrometer PANTHER; and a second protein crystallography station, DALI. The D3 hot-neutron diffractometer and IN20 thermal triple-axis spectrometer have been upgraded while new and additional detectors for the SANS instruments D11 and D22 have been installed. The D16 cold-neutron diffractometer has been fully modernised and new coldneutron imaging instrument, NeXT, has been installed. Delivering a full suite of modernised instrumentation is dependent on the renewed in-pile beam extraction, H1-H2, new H24 (thermal) and H15 (cold) neutron guides and the in-house development and manufacture of critical technologies such as neutron detectors, monochromator optics and polarisation components. The new H24 guide provides dedicated endof-guide positions to the upgraded D10+ single crystal diffractometer, IN13 backscattering instrument and the new XtremeD powder and single-crystal diffractometer. H15 will accommodate a substantially upgraded D(00)7 polarised diffuse scattering and spectroscopy instrument while D11 will be rebuilt and relocated with an optically cleaner collimation. Two additional end-of-guide positions are available for new instrumentation: The SHARP+ cold-neutron TOF spectrometer and a 4th SANS instrument, SAM. The success of Endurance will provide users with a fully modernised suite of world-class instruments.

Simulating Araponga - The High-Resolution Diffractometer of Brazilian Multipurpose Reactor

The Brazilian Multipurpose Reactor (RMB) is a fundamental project that aims to turn Brazil into a self-sufficient country in the production of radioisotopes and radiopharmaceuticals to supply the Unified Health System (SUS) as much as the private institutions. In addition, the RMB project describes other applications as irradiation and testing of nuclear fuels and structural material analysis, for instance. There are many techniques in the project to study structural aspects of materials, where neutron diffraction represents one of the priorities for implementation. This technique will take place mainly on two diffractometers on Thermal Neutron Guide 1 (TG1), namely Araponga, a high-resolution diffractometer, and Flautim, a high-intensity diffractometer. In this work, we study the performance of the Araponga diffractometer through McStas simulations with input produced by the MCNP code of the RMB core. We investigate the neutron flux values considering a state-of-art high-resolution diffractometer, and the results are promising since some simulated scenarios present values compatible with high-intensity devices.

Nested mirror optics for neutron extraction, transport, and focusing

Neutron scattering is a well-established tool for the investigation of the static and dynamic properties of condensed matter systems over a wide range of spatial and temporal scales. Many studies of high interest, however, can only be performed on small samples and typically require elaborate environments for variation of parameters such as temperature, magnetic field and pressure. To improve the achievable signal-to-background ratio, focusing devices based on elliptic or parabolic neutron guides or Montel mirrors have been implemented. Here we report an experimental demonstration of a nested mirror optics (NMO), which overcomes some of the disadvantages of such devices. While even simpler than the original Wolter design, our compact assembly of elliptic mirrors images neutrons from a source to a target, reducing geometric aberrations, gravitational effects and waviness-induced blurring. Experiments performed at MIRA at FRM-II demonstrate the expected focusing properties and a beam transport efficiency of 72% for our first prototype. NMO seem particularly well-suited to (i) extraction of neutrons from compact high-brilliance neutron moderators, (ii) general neutron transport, and (iii) focusing and polarizing neutrons. The phase space of the neutrons hitting a sample can be tailored on-line to the needed experimental resolution, resulting in small scattering backgrounds. As additional benefits, NMO situated far away from both the moderator and the sample are less susceptible to radiation damage and can easily be replaced. NMO enable a modular and physically transparent realization of beam lines for neutron physics similar to setups used in visible light optics.

High‐Pressure Studies of Correlated Electron Systems

Tuning the electronic properties of transition‐metal and rare‐earth compounds by virtue of changes of the crystallographic lattice constants offers controlled access to new forms of order. The development of tungsten carbide (WC) and moissanite Bridgman cells conceived for studies of the electrical resistivity up to 10 GPa, as well as bespoke diamond anvil cells (DACs) developed for neutron depolarization studies up to 20 GPa is reviewed. For the DACs, the applied pressure changes as a function of temperature in quantitative agreement with the thermal expansion of the pressure cell. A setup is described that is based on focusing neutron guides for measurements of the depolarization of a neutron beam by samples in a DAC. The technical progress is illustrated in terms of three examples. Measurements of the resistivity and neutron depolarization provide evidence of ferromagnetic order in SrRuO3up to 14 GPa close to a putative quantum phase transition. Combining hydrostatic, uniaxial, and quasi‐hydrostatic pressure, the emergence of incipient superconductivity in CrB2is observed. The temperature dependence of the electrical resistivity in is consistent with emergent Kondo correlations and an enhanced coupling of magneto‐elastic excitations with the conduction electrons at low and intermediate temperatures, respectively.

A non-depolarizing CuTi neutron supermirror guide for PERC

Neutron guides are used to transport slow neutrons from sources to experiments. Conventional neutron supermirror guides use alternating thin layers based on nickel and titanium. Due to the magnetic properties of nickel, their neutron reflection properties are spin-dependent, in particular when exposed to high magnetic fields. Motivated by the requirements of precision experiments on neutron beta decay, we present novel supermirrors based on copper and titanium, which preserve the neutron beam polarization. These show excellent reflectivity and prove to be very stable even when exposed to high temperatures.

Monte Carlo simulations of the S-shaped neutron guides with asymmetric concave and convex surface coatings

During the last decades, neutron beam transportation has been a well-known and established subject of designing proper neutron guides. However, sometimes unusual adaptation or adjustments are required out of original projects and after the operation beginning of facilities. An inter-center transfer of instrument locations also requires a new approach that is not described in detail in the literature. Inside these situations, the use of S-shaped guides has not been fully discussed in the literature. From a geometrical analysis, we have developed a construction formalism of a minimal S-shaped guide by only considering the exclusion of the Line-of-Sight. The guide model has been studied through the wavelength cutoff and the neutron transport efficiency analysis. Here, Monte Carlo simulations using MCSTAS software have been applied. By intending to optimize these guide systems, simulations of this study also consider scenarios that have different supermirrors. A formalism to determine wavelength cutoff for unique and variable index guide systems has also been developed. There is a good correspondence between the theoretical cutoff wavelength values and the corresponding values obtained through Monte Carlo simulations. In addition, we have found specific configurations that combine efficient neutron transport and lower m-values on the convex surfaces of curved guides that form the S-shaped guide.

Neutron guide optimization for the Moroccan PGAA system

The Moroccan TRIGA Mark II research reactor is to be equipped with a PGAA (Prompt Gamma Activation Analysis) facility to assist the country's progression in socioeconomic areas such as the environment and geochemistry, agriculture, health, industry, cultural heritage, and human sciences. The requirements of the PGAA facility include a very high thermal to fast neutron flux ratio and a focused, thin beam. Supermirror neutron guides are generally used to meet such requirements due to their ability to reflect neutrons with a specific energy and scattering angle. This study was undertaken to determine a suitable neutron guide for achieving optimal performance for the PGAA facility, where such a determination needs to be made according to both the available space and the minimum performance needed for PGAA analysis. To better parameterize the neutron guide, a set of simulations were performed with the aim of establishing the best guide specifications. Three types of neutron guides were studied, namely straight, curved, and bender. McStas code was used in this study, and the simulations showed that the guides must be 6 m long and that the coating value m must be equal to 5 for the bender and straight guides and 6 for the curved guide. Among the three guide types, the thermal/epithermal (Фth/Фep) and thermal/fast (Фth/Фfast) ratios were found to be much better when using the curved guide.

Self-shielding copper substrate neutron supermirror guides

The invention of self-shielding copper substrate neutron guides is described, along with the rationale behind the development, and the realisation of commercial supply. The relative advantages with respect to existing technologies are quantified. These include ease of manufacture, long lifetime, increased thermal conductivity, and enhanced fast neutron attenuation in the keV-MeV energy range. Whilst the activation of copper is initially higher than for other material options, for the full energy spectrum, many of the isotopes are short-lived, so that for realistic maintenance access times the radiation dose to workers is expected to be lower than steel and in the lowest zoning category for radiation safety outside the spallation target monolith. There is no impact on neutron reflectivity performance relative to established alternatives, and the manufacturing cost is similar to other polished metal substrates.

Study on s-shaped guide using mcstas software

Monte Carlo simulations are performed for a vertical S-shaped neutron guide for the cold neutron sources of the FRM-II, HZB and PSI reactors through the McStas software. The aim of our study is investigate a relation between the cutoff in the cold neutron spectrum and the sources. Results for the neutron flux at the sample position are presented for different supermirrors with m = 1, 2 and 3. The vertical S-shaped neutron guides additionally provide a vertical displacement between beam hole and sample position, which can facilitate the implementation and manipulation of sample environments.

SINQ—Performance of the New Neutron Delivery System

The Swiss spallation neutron source SINQ at Paul Scherrer Institute (PSI) has been in operation since 1996 using an optical guide system to transport low-energy neutrons from the source to the neutron beam lines. Clear signs of degradation in the guide system motivated us to redesign all neutron guides, which were then replaced in 2019–2020. All instruments received new tailored guides and SINQ operation was resumed in July 2020. Neutron flux measurements before and after the upgrade show that the expected instrument-dependent flux gain of a factor 2–10 was achieved. Furthermore, the fast-neutron background in the guide hall could be suppressed with an improved shielding in the guide bunker. The upgrade was completed with a slight delay due to the corona pandemic and in full compliance with the financial budget.

Graphite intercalation compound (GIC) crystal monochromators for cold neutron instruments: Characterization of KC24 by time-of-flight neutron diffraction.

Graphite intercalation compounds (GICs) are a group of layered materials that are suitable as monochromators for cold neutrons. KC24 is a particularly interesting compound in this regard as it features a large c-axis lattice spacing of 8.74 Å, high reflectivity, and the possibility to produce large crystals with mosaicity that matches the beam divergence of cold neutron guides. GICs can be synthesized with different levels of intercalation, known as the stage of the compounds. Each stage displays a specific d-spacing. Impure GIC-monochromators containing multiple stages produce mixing of neutron wavelengths, which complicates data analysis on neutron reflectometers. We discuss the implications of GIC crystal purity and stage contamination for neutron reflectometry and show how GIC crystals can be characterized by time-of-flight neutron diffraction providing an efficient and quantifiable measure of the reflected wavelength spectrum. This allows taking into account multiple wavelength contaminations and ascertains the robustness of reflectometry measurements.

Neutrons for Battery Research (in-situ and operando studies): An Overview

The further development of battery materials and cells must go hand in hand with improved in-situ and operando characterization methods. Such techniques provide a better and deeper understanding of the mechanisms to determine even minor changes in cell components and their impact on the overall performance of cells and their capacity or battery life.The last ten years there has been a great deal of interest in scattering techniques for examining battery components and in particular complete cells [1]. Neutrons as a probe or techniques derived from neutrons play a special role in this development because their unique properties and possibilities are very well suited for battery research. On the one hand, neutrons can penetrate deep into materials and on the other hand, they are very sensitive to light elements as Li, H or N. In addition, neutron methods are non-destructive, which makes it possible to measure the inner part of a cell as well as to perform operando measurements. Improvements of neutron instrumentation including coatings of neutron guides, higher counting rates of detector systems and dedicated sample environments. Further the higher neutron flux of modern neutron large scale facilities accelerate the development of neutrons for battery research. In-situ and operando studies while changing external parameters such as charging/discharging or temperature change etc. are carried out to examine cells under real working conditions.Neutron diffraction, small-angle neutron scattering, neutron imaging and neutron depth profiling are considered among the most suitable methods for battery research. This contribution presents typical applications of these different neutron methods, which are used on different length scales. Neutron diffraction and small-angle neutron scattering are suitable to investigate changes from the atomic scale up to the mesoscopic scale (~ 300 nm). Processes such as Li intercalation in graphite anodes during battery charging can be described in detail [2,3]. Neutron imaging is suitable to follow in-situ the electrolyte filling process in hard case cells [4]. The neutron depth profiling technique is applied for studies of the Lithium mobility at the different electrode interfaces to determine the Li concentration profile in approximately the first 50 mm [5], e.g. the SEI layer [6]. Reference s : [1] R. Gilles, Journal of Surface and Investigations: X-ray, Synchrotron and Neutron Techniques (2020), in print.[2] V. Zinth et al., Journal of Power Sources 361 (2017) 54-60.[3] J. Hattendorff et al., J. Appl. Cryst. (2020), 53, 210-221.[4] W. J. Weydanz et al., Journal of Power Sources 380 (2018) 126-134.[5] M. Trunk et al., Materials Characterization (2018), 146, 127-134.[6] S. Whitney et al., Journal of the Electrochemistry Society (2009), 156(11) A886.

Effects of ground movements on realistic guide models for the European Spallation Source

We model the effect of ground movement, based on empirical experience, on the transport properties of long neutron guides by ray-tracing simulations. Our results reproduce the large losses found by an earlier study for a simple model, while for a more realistic engineering model of guide mounting, we find the losses to be significantly smaller than earlier predicted. A detailed study of the guide for the cold neutron spectrometer BIFROST at the European Spallation Source shows that the loss is 7.0(5) % for wavelengths of 2.3-4.0 {\AA}; the typical operational wavelength range of the instrument. This amount of loss does not call for mitigation by overillumination as suggested in the previous work. Our work serves to quantify the robustness of the transport properties of long neutron guides, in construction or planning at neutron facilities worldwide.

Prompt Gamma Shielding of Neutron Guides from Ray-Tracing Monte Carlo Simulations

This communication provides a brief overview of an efficient, fast, and computationally inexpensive method for evaluating the contribution of prompt gamma rays to dose rate around shielded neutron guides. Parameterized probabilities for neutron absorption in the materials of the neutron guide coatings during reflection were implemented in McStas ray-tracing simulation software together with analytical formula and tabular data necessary for a numerical evaluation of a dose equivalent. This allows evaluating the dose rate beyond the lateral shielding upon simulation of the guide ray-tracing.

Neutronic Calculations for the Shielding Design of the VESPA Instrument at the European Spallation Source

The European Spallation Source is being built in Lund, Sweden and it’s planned to be the brightest pulsed spallation source for thermal and cold neutrons (<1 eV). Neutrons will be produced by a 2 GeV accelerated proton beam hitting a tungsten target wheel, then they are moderated by liquid hydrogen and water based moderator system and delivered to 42 beam-ports. Neutrons are transported via reflections to a set of instruments connected to the beam-ports through neutron guides. Undesired fast neutrons can cause a radiation safety issue, since they can find their way down the beam-lines and thus generate a large dose. A designed shielding structure is needed to minimize such effect during the beam at the target phase. We present the results of neutronic calculations to optimize the guide shielding for the VESPA instrument.

Fabrication and testing of high-performance all-metal neutron guides and axisymmetric mirrors by electrochemical replication

ABSTRACTNeutron scattering is one of the most useful methods of studying the structure of matter, with applications to biomedical, structural, magnetic and energy-related materials. Neutron-scattering instruments are installed around research reactors or accelerator-based neutron sources, and neutron guides are critical components of these facilities. They are neutron-transport optical devices consisting of state-of-the-art mirrors often tens of meters long. Here we demonstrate a novel fabrication method of all-metallic neutron guides and axisymmetric mirrors by electroplating from precision mandrels. The process allows for the fabrication of single-piece all-metal guides of prismatic and axisymmetric shapes. We also demonstrate supermirror guides and axisymmetric focusing supermirrors produced with the same technology. We present the fabrication and tests of the multilayer-coated replicated guides and optic and show that the mandrel is reproduced with high fidelity and reliability. Such supermirror optics will provide game-changing improvements in neutron techniques.

Neutron Guide Building instruments of the Brazilian Multipurpose Reactor (RMB) project

A growing community of scientists has been using neutrons in the most diverse areas of science. In order to meet the researchers demand in the areas of physics, chemistry, materials sciences, engineering, cultural heritage, biology and earth sciences, the Brazilian Multipurpose Reactor (RMB) will provide 3 thermal guides and 3 cold guides, with the installation of several instruments for materials characterization. In this study, we present a standard design requirement of two primordial instruments, namely Sabi'a and Araponga. They are, respectively, cold and thermal neutron instruments and correspond to a Small-Angle Neutron Scattering (SANS) and High-Resolution Powder Neutron Diffractometer (HRPND) to be installed in the Neutron Guide Building (N02) of RMB . To provide adequate flux for both instruments, we propose here an initial investigation of the use of simple and split guides to transport neutron beams to two different instruments on the same guide. For this purpose, we use Monte Carlo simulations utilizing McStas software to check the efficiency of thermal neutron transport for different basic configuration and sources. By considering these results, it is possible to conclude that the split guide configuration is, in most cases, more efficient than cases that use transmitted neutron beams independently of source. We also verify that the employment of different coating indexes for concave and convex surfaces on curved guides is crucial, at least on simulated cases, to optimise neutron flux (intensity and divergence) and diminish facility installation cost.

The Garrett approximation revisited

Three variants of the Garrett approximation are studied, and their accuracy is analyzed, for symmetric and asymmetric square wells. Quite surprisingly, the simplest variants are also the most accurate. Their application to quantum wells, quantum dots, and capillary neutron guides are briefly discussed.