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The general performance of diffractometers at the first long pulse spallation source ESS, is compared with their counterparts at J-PARC, a short pulse spallation source. The difference in the inherent pulse structure of these neutron sources presents opportunities for new concepts for instrumentation, where performance does not scale simply with source power. The article describes advantages and disadvantages of those diffractometers, adapting to the very different source characteristics. We find that the two sources offer comparable performance in flux and resolution when operating in high-resolution mode. ESS offers significant advantages in tunability and flexibility, notably in the ability to relax resolution in order to increase flux for a given experiment. The slow repetition rate of ESS favors long instruments. On the other hand, J-PARC instruments perform very well in spite of the lower source power and allow better access to epithermal neutrons, of particular interest for PDF analysis of diffraction data.

Canada’s access to neutron beams for neutron scattering was significantly curtailed in 2018 with the closure of the National Research Universal (NRU) reactor in Chalk River, Ontario, Canada. New sources are needed for the long-term; otherwise, access will only become harder as the global supply shrinks. Compact Accelerator-based Neutron Sources (CANS) offer the possibility of an intense source of neutrons with a capital cost significantly lower than spallation sources. In this paper, we propose a CANS for Canada. The proposal is staged with the first stage offering a medium neutron flux, linear accelerator-based approach for neutron scattering that is also coupled with a boron neutron capture therapy (BNCT) station and a positron emission tomography (PET) isotope production station. The first stage will serve as a prototype for a second stage: a higher brightness, higher cost facility that could be viewed as a national centre for neutron applications.

Beryllium reflectors are used at spallation neutron sources in order to enhance the low-energy flux of neutrons emanating from the surface of a cold and thermal moderator. The design of such a moderator/reflector system is typically carried out using detailed Monte-Carlo simulations, where the beryllium reflector is assumed to behave as a poly-crystalline material. In reality, however, inhomogeneities in the beryllium could lead to discrepancies between the performance of the actual system when compared to the modeled system. The dependence of the total cross-section in particular on crystallite size, in the Bragg scattering region, could influence the reflector performance, and if such an effect is significant, it should be taken into account in the design of the moderator/reflector system. In this paper, we report on the preliminary results of using cross-section libraries, which include corrections for the crystallite size effect, in spallation source neutronics calculations.

The European Spallation Source being constructed in Lund, Sweden will provide the user community with a neutron source of unprecedented brightness. By 2025, a suite of 15 instruments will be served by a high-brightness moderator system placed above the spallation target. The ESS infrastructure, consisting of the proton linac, the target station, and the instrument halls, allows for implementation of a second source below the spallation target. We propose to develop a second neutron source with a high-intensity moderator able to (1) deliver a larger total cold neutron flux, (2) provide high intensities at longer wavelengths in the spectral regions of Cold (4–10 Å), Very Cold (10–40 Å), and Ultra Cold (several 100 Å) neutrons, as opposed to Thermal and Cold neutrons delivered by the top moderator. Offering both unprecedented brilliance, flux, and spectral range in a single facility, this upgrade will make ESS the most versatile neutron source in the world and will further strengthen the leadership of Europe in neutron science. The new source will boost several areas of condensed matter research such as imaging and spin-echo, and will provide outstanding opportunities in fundamental physics investigations of the laws of nature at a precision unattainable anywhere else. At the heart of the proposed system is a volumetric liquid deuterium moderator. Based on proven technology, its performance will be optimized in a detailed engineering study. This moderator will be complemented by secondary sources to provide intense beams of Very- and Ultra-Cold Neutrons.

The McStas neutron ray-tracing simulation package is a collaboration between Riso DTU, ILL, University of Copenhagen and the PSI. During its lifetime, McStas has evolved to become the world leading software in the area of neutron scattering simulations for instrument design, optimisation, virtual experiments and science. McStas is being actively used for the design-update of the European Spallation Source (ESS) in Lund. This paper includes an introduction to the McStas package, recent and ongoing simulation projects. Further, new features in releases McStas 1.12c and 2.0 are discussed.

Even the most powerful steady-state neutron sources do not deliver sufficient flux for neutron imaging with microsecond time resolution. The future pulsed neutron spallation sources will offer a much higher peak flux, but have a low repetition rate that makes sequential data collection and synchronization for repetitive motions rather difficult. This paper proposes an asynchronous data collection scheme for recording movies of fast continuous repetitive motions like running combustion engines.

Simulation of an inelastic scattering experiment, with a sample and a large pixilated detector, usually requires days of time because of finite processor speeds. We report simulations on an spallation neutron source (SNS) instrument, SEQUOIA, that reduce the time to less than 2 h by using parallelization and the resources of the TeraGrid. SEQUOIA is a fine resolution (ΔE/E i∼1%) chopper spectrometer under construction at the SNS. It utilizes incident energies from E i = 20 meV–2 eV and will have ∼144,000 detector pixels covering 1.6 Sr of solid angle. The full spectrometer, including a 1-D dispersive sample, has been simulated using the Monte Carlo package McStas. This paper summarizes the method of parallelization for and results from these simulations. In addition, limitations of and proposed improvements to current analysis software will be discussed.

Crystal monochromator-Fermi-chopper (FC) (X-TOF) instruments provide a high count-rate with flexible resolution optimization. We show that the most advantageous range of operation for this class of instruments falls in the thermal and sub-thermal range where focusing Bragg optics can be used to full benefit. In this spectral window, an X-TOF instrument at a high-flux reactor can match a chopper spectrometer on a MW power short pulse spallation source as can be shown by comparing the optimized concepts. The high count-rate makes this type of instrument highly attractive for polarized neutron operation. Recent experiments performed using a new large solid-angle 3He neutron spin-filter represent a significant breakthrough in the field of neutron polarization analysis studies on multi-detector spectrometers, forming the basis of the proposed PASTIS project which enables xyz-polarization analysis studies on a thermal TOF spectrometer (Stride et al., Stewart et al.). Outlook for implementation of PASTIS as a th...

A small-angle detector will complete the performance of the cold time-of-flight spectrometer FOCUS at the Swiss Spallation Source SINQ of the Paul Scherrer Institute, Villigen, Switzerland. It is constructed from position-sensitive 3He tubes located 2.5 m away from the sample, and covers an area of about 95 × 70 cm2 with a spatial resolution of approximately 1.5 cm. The 2D detector is located within a vacuum chamber, next to the argon chamber of the existing large angle detectors, and covers an angular range from 2 to 22°. Commissioning of the 2D small angle detector will start in spring 2006.

The possibilities of neutron investigations of the magnetic structure of crystals at powerful pulsed neutron sources, JSNS (Japan), TIRAN (Snezhinsk, Russia) and LHC (CERN), with the use of pulsed magnetic fields are considered. An opportunity for diffraction measurements of magnetic phases induced by magnetic fields up to 800–1000 kOe at the TIRAN reactor and the spallation source at the LHC accelerator is shown.

Polarized neutrons provide a powerful tool for research at today's continuous neutron sources, permitting unique information to be obtained from neutron-scattering experiments and in the area of fundamental neutron physics. The information obtained is indispensable to important areas of current research such as magnetism, spin fluctuations in correlated-electron materials, nanoscience, astrophysics, and cosmology. Unfortunately, the polarized neutron capabilities that already exist at reactor neutron sources, mainly in Europe, cannot be transferred directly to pulsed spallation sources because many of the devices used at reactors to manipulate neutron spins operate only at a single neutron wavelength or with a neutron beam of limited divergence. Both of these restrictions must be overcome for devices to be useful at pulsed spallation sources. This report identifies the significant R&D efforts that will be required to achieve these goals. These efforts must be undertaken now, if they are to be useful early...

We present the results of a Monte Carlo simulation and analytical calculations for a phase space transformer, which accelerates ultra-cold neutrons (UCNs) to cold or thermal neutron energies. We show that due to the sharp energy distribution of UCN's this kind of neutron device is able to produce monochromatized neutrons with intensities competing today's most performing time-of-flight instruments, an energy resolution of the order of δE/E∼0.3%, and a horizontal divergency of ∼2° at the planned spallation source for UCN's (PSI, Switzerland).

New superionic glasses (CuI)x(AgPO3)1−x with x=0.1, 0.2 and 0.3 have been prepared by rapid quenching method. Neutron diffraction experiments have been performed by a HIT-II spectrometer at the Neutron Spallation Source, KEK, Japan. A small first diffraction peak at low Q around 0.8 A was observed in the structure factor for x=0.2 and x=0.3, but for x=0.1 it shows only a shoulder that is similar to the undoped glass AgPO3. Three new peaks appear at the radial distribution function of (CuI)x(AgPO3)1−x at ∼ 1.9, 2.7 and 3.4 A, that may correspond to the Cu-O, Cu-I and Cu-Cu pair correlations, respectively. Those peaks increase with the amount of CuI. These results indicate that there are two different kinds of Cu atoms. Cu-I bond in the glass is very similar to that in crystalline α-CuI, and Cu-O bond is very similar to that in Cu2O insulating crystal.

Julich Experimental Spallation Target Set-up In COSY Area (JESSICA) is a full-scale model of the target-reflector-moderator system for the European Spallation Source (ESS), which has been built up at the COSY accelerator in the research centre Juelich. JESSICA has been designed for prototyping experiments for the ESS and to validate simulation methods concerning the transport and interaction of particles as well as to optimize the technical layout of the target-reflector-moderator system and to compare the results by using different moderator materials. This year JESSICA will become operational with one cryogenic moderator and one ambient below the target, and two ambient moderators above it. For the cryogenic moderator, different moderator materials will be used. a. Liquid hydrogen b. Solid methane as a block c. Solid methane pellets surrounded by liquid hydrogen. The engineering design of JESSICA, including the cryogenic moderator system and safety aspects, will be discussed.

We explore methods for making detailed calculations on the neutronic performance of a pelletised moderator, wherein a significant fraction of the moderating medium is heterogeneously distributed. This pellet approach appears to be necessary to provide cooling capabilities to a solid moderator material under heavy heat loads, and furthermore appears to offer the only realistic mechanism for permitting solid moderators in situations where the moderator material stores energy from radiation damage at a significant rate. Current use of solid moderators (e.g. methane at the Intense Pulsed Neutron Source facility) is significantly limited by the need to avoid catastrophic release of this stored energy.

Neutronic performance of coupled and decoupled hydrogen moderators for a short pulse spallation source was extensively studied by calculations to seek the optimal parameters, especially the para/ortho hydrogen ratio. A decoupled 100% para-hydrogen moderator gives excellent pulse characteristics at lower energies. Gadolinium (Gd) poisoning is useful to obtain narrower pulses up to about 70 meV at a reasonable intensity penalty. At higher energies, where the pulse tail decay characteristics become most important, the choice of the reflector material and the decoupling energy (E d) play an important role. One important technical issue is the radiation damage of a Gd-poison and a boron carbide decoupler. We discuss the possibility of using a composite decoupler material such as Cd+In (indium)+Eu (europium). In a coupled moderator a 100% para-hydrogen moderator of a larger volume gives an additional intensity gain over a normal one but the gain is not as large as in a decoupled one.

The new time-of-flight diffractometer for strain-field measurements POLDI at the continuous spallation source SINQ at PSI is presented. High intensity and high resolution are achieved simultaneously by allowing pulse overlapping. The dependence of the arrival time of the neutrons in the detector on the scattering angle allows the calculation of the diffraction pattern. The basic concept and the main instrument components are presented in this paper.

2The present work concentrates on comparing a numerical code and a closed-form analytic solution for determining transient stress waves generated by an impinging, high-intensity proton pulse onto a perfectly elastic solid cylindrical target. The comparison of the two methods serves both to benchmark the physics and numerical methods of the codes, and to verify them against analytic expressions that can be established for calculating the response of the target for simple cases of loading and geometry. Additionally, the comparison elucidated the effects of approximation s used in the computation of the analytic results. Two load cases have been investigated: (1) an instantaneous ly uniform thermal loading along the central core, and (2) a ramped and uniform thermal load applied along the central core. In addition, the influence of the approximations applied to the accurate analytic forms has been elucidated. By validating these analytical results, the closed-form solution may be confidently used to "bound" the solution prior to initiating more detailed and comprehensive numerical studies.

We carried out an experiment on neutron yields from typical cylindrical lead targets for 12-GeV protons by means of the Mn-bath moderation method. Our experimental results are, roughly speaking, consistent with those by Russian groups done for lower energy protons by different methods. The number of neutrons absorbed in the Mn-bath was determined to be 195 neutrons/proton, and the total neutron yield, including leakage neutrons, which were evaluated by calculations, was estimated to be 201 neutrons/proton for a 20cm (diameter) × 60cm (length) lead target. The total neutron yield as a function of the proton energy Ep, fitted to our data and the results of others, is expressed by the formula 2.0 + 29.2Ep 0.78, where Ep is expressed in GeV.

Suitable instruments on spallation neutron sources are ideal for diffraction studies of proteins and oriented molecular complexes (Schoenborn, 1992a). With spallation neutrons and their time dependent wavelength structure, diffraction data may be readily selected electronically with an optimal wavelength bandwidth and cover the whole Laue spectrum as time (wavelength) resolved spectra. This optimizes data quality with best peak-to-background ratios and provides adequate spatial and energy resolution to eliminate diffraction peak overlaps. To maximize flux within this energy range a partially decoupled moderator concept will be discussed using calculated flux profiles, and the impact on calculated diffraction data assessed.

The expected performance of single-crystal time-of-flight diffraction at a potential long pulse spallation source is discussed for both small and large-unit-cell structures. The requirements and capabilities in biomacromolecular structure analysis at high, atomic resolution are focused on. Data collection times are predicted on the basis of a detailed evaluation of the counting-statistical quality of a complete data set. It is found that a long pulse source would excel the capabilities at the best existing steady state source. Most promising for advances in the more challenging structural problems, however, looks a short pulse spallation source with an intermediate-temperature coupled moderator.

The layout criteria for a reflectometer at a long pulse spallation source (LPSS) are discussed. It is shown how the most important instrument parameter, the wished resolution of the measured reflectivity profile, determines the choice of the wavelength and available wavelength band, the length of the instrument and the position of the disc choppers, which are necessary for applying the time-of-flight method. Using 4 disc choppers it is possible to measure the same spectrum with different resolutions without changing the beam geometry and the available wavelength band. All considerations are tested with Monte Carlo simulations, which were performed with a 2 ms pulse of a source working at 25 Hz.

There are potential gains of about a factor of seven in the time-average neutron brightness for a coupled liquid H2 moderator compared to a decoupled one, and a factor of around five for a H2O moderator. However, these gains come at the expense of putting “tails” on the neutron pulses. The particulars of the neutron pulses from a moderator (e.g., energy-dependent rise times, peak intensities, pulse widths, and decay constant(s) of the tails) are crucial parameters for designing instruments and estimating their performance at an LPSS. The spallation target system designer can alter moderator neutronic performance by: (a) the choice of target material and geometry; (b) proper selection of the moderator material and geometry; (c) varying the target—moderator geometry; (d) the choice of reflector material(s); (e) the presence/absence of decouplers and liners; and (f) the proton pulse width. A 1-MW Long-Pulse Spallation Source (LPSS) has world-class neutronic performance. We show that the calculated p...

We studied the design and performance of a small-angle neutron scattering (SANS) instrument for a proposed 1 MW, 60 Hz long pulsed spallation source at the Los Alamos Neutron Science Center (LANSCE). An analysis of the effects of source characteristics and chopper performance combined with instrument simulations using the LANSCE Monte Carlo instrument simulations package shows that the T 0 chopper should be no more than 5 m from the source with the frame overlap and frame definition choppers at 5.6 and greater than 7 m, respectively. The study showed that an optimal pulse structure has an exponential decaying tail with τ ≈ 750 μs. The Monte Carlo simulations were used to optimize the LPSS SANS, showing that an optimal length is 18 m. The simulations show that an instrument with variable length is best to match the needs of a given measurement. The performance of the optimized LPSS instrument was found to be comparable with present world standard instruments.

Experimental results on neutron currents and storage times of both ambient temperature H2O and liquid H2 cryogenic moderators in various target and reflector environments are presented. These results are compared with measured neutron currents from both a representative thermal beam and the new horizontal cold D2 source at the ILL with respect to expected performances of pulsed sources. The results of the spallation experiments are compared with Monte Carlo calculations from Los Alamos. Based on the measured moderator storage times r the consequences of different proton pulse characteristics on the performance of neutron scattering instruments are discussed in general for both ambient temperature and cryogenic moderators. The possible gain of pulsed operation for time-of-flight and continuous source applications is outlined. In particular, small angle neutron scattering (SANS), a classical technique at a continuous source is taken as an example to show the pros and cons of different source concep...

Design criteria for a NSE spectrometer at a LPSS are discussed. First results of Monte Carlo simulations, which were performed to quantify the performance of the instrument in typical quasielastic experiments on soft matter samples, are presented. Typical quasielastic scattering functions in the small wave number range for this kind of samples lead to convenient matching between the wavelength dependence of the instrument parameters and the wave number dependence of the scattering.

The performance of a Laue diffractometer at a Long Pulse Spallation Source is illustrated by an example. The instrument is built at a thermal f = 25 Hz source and uses a neutron guide, which is 70 m long, and a wavelength band of 2 A at the position of the sample. The pulse of 2 ms of the source can be chopped to provide a variable resolution of the order δλ/λ = 1–3%. The instrument is suited for the investigation of samples with unit cell volumes of the order of 100–1000 A3 at a medium time resolution. For an averaged spallation beam power of 5MW the neutron flux at the sample position is estimated to amount to Φ = 3–8 × 107 n cm−2s−1, depending on the chopper speed. The performance of the instrument is demonstrated by a Monte Carlo simulation technique. Calculations with an idealised model sample focus on the peak-to-background ratio and the ability to resolve Bragg peaks.

The neutronic performance of a coupled grooved moderator of liquid-hydrogen was experimentally studied and from the measured neutronic performance it was proved that this type of grooved moderator is useful not only for short pulse spallation sources but also for long pulse spallation sources.

Using a Monte Carlo simulation method for calculating the proton and neutron flux distribution a symmetrical geometry—two targets surrounding a side moderator—is proposed for the target station of a spallation source. Mesitylene possessing high stability against radiation damage is discussed as a possible material for the cold source.

Ultra Cold Neutrons (UCN) can be produced at spallation sources using a variety of techniques. To date the technique used has been to Bragg scatter and Doppler shift cold neutrons into UCN from a moving crystal. This is particularly applicable to short-pulse spallation sources and is the method planned for a UCN source that is under construction at LANSCE. However, large gains should be possible using cryogenic UCN sources. Spallation sources are particularly well suited for such sources given the lower heat loads and simpler engineering requirements than are possible at a reactor. The most attractive cryogenic source appears to be a frozen deuterium source and research is under way at Gatchina to demonstrate technical feasibility. If successful, a source of this type could be implemented at future spallation sources with a UCN density that may be two orders of magnitude higher than that presently available at reactors.

The paper presents the spectrum of solid state neutron scintillation detectors, which have been developed and manufactured at Julich with respect to use at neutron scattering instruments at steady state reactors and pulsed spallation sources. Design and physical characteristics of three types of linear and three types of area detectors are described. The detectors are designed for operation as standalone PC-based systems with integrated timing interface based on programmable logic cell arrays. The data acquisiton system within the EISA-PC is suitable for applications requiring huge amounts of memory, e.g. in position-sensitive time-of-flight experiments.

The results of test measurements carried out at the ISIS spallation source on a prototype double-crystal analyser system are reported. Based upon the results of these test measurements, a multi-double-crystal analyser system has been designed for use on the PRISMA spectrometer and is under construction at the Istituto di Struttura della Materia del Consiglio Nazionale delle Ricerche, Frascati, Italy. This new analyser system will allow experiments to be carried out on PRISMA with low analysing energies (Ef,min = 2.25meV).

Arguments on advantages and disadvantages of TOF against TAS are quite old and the situation for single crystals seemed clear for many years. But the advent of spallation sources restimula...

Neutron spin echo (NSE) is the method which can achieve the highest energy resolution in quasielastic neutron scattering. It is now well established at different steady state neutron sources. It appears that the next generation neutron sources will all be of pulsed spallation type. IN15, the high resolution NSE at the ILL in Grenoble, has a chopper system to work in Time of Flight mode and has demonstrated the technical feasibility and tested the possible advantages of operating in this mode. In soft matter and biological studies, in the great majority of cases, the samples have some characteristics which happen to be very favorable for TOF-NSE and this is what we will try to demonstrate.

At neutron energies below about 3 meV, a disk chopper can produce shorter pulses than spallation-source cold moderators. The development of mica crystal-analyzer spectrometers at spallation sources has led to the use of energies well below 1 meV, where the shorter pulse of the disk chopper at a reactor cold-source can be exploited to build an instrument almost ten times shorter than its spallation-source counterpart. A short flight-path instrument has advantages for energy-range, total count-rate, and cost.

The fast neutrons produced by the spallation process are slowed down to velocities adequate for neutron scattering experiments by a complex target-reflector-moderator system. The neutron performance of a spallation source depends decisively on the design and efficiency of this system. In spite of decades of accumulated experience, target-moderator systems still present major challenges in terms of understanding the basic principles and relationships, numerical and optimisation approaches and engineering solutions. A particularly important aspect is the interplay between moderator performance and instrument design. This is a twoway street: the desires of instrument builders provide important input for the target people. At the same time, it is in the best interest of instrument builders to have an understanding of what happens in the target and moderators, to appreciate potentials and difficulties. This interaction between the two sides will help us get the most out of future spallation sources. In order to promote this process, Hahn-Meitner-Institut, as the lead laboratory for the ESS instrumentation task, organised an international workshop on 12–14 March 2001, in order to review the current state of moderator development and requirement by neutron instrumentation. The workshop was generously supported by a grant from the EU Neutron Round Table. About 40 participants attended, with strong contributions by the American and Japanese communities as well as from Europe. Constructive and lively discussions on the various aspects of the workshop topic demonstrated the importance of moderator design, target-moderator set-up and requirements by neutron instrumentation for future spallation sources. Although most presentations given during the workshop are published in the present volume, due to the very preliminary status of results, some work as recent calculations by Filges et al. on the neutronic performance of moderators for ESS appears elsewhere. The presented results and discussions will have an important influence on the ESS moderator and instrumentation R and D as well as other spallation source projects.