Table of contents

Every two–three years scientists involved in developments of neutron optics gather together for the International Workshop on Neutron Optics (NOP). Neutron optics has always been considered very important for the development of new neutron instrumentation. The limited brilliance of existing or future neutron sources requires the more effective usage of emitted neutrons. Indeed, improvements of the neutron optical system or an optimization of the neutron–optical tracts of instruments can result in a significant enhancement of their performance. This is especially important at present when the neutron scattering community is strongly engaged in developments of new instrumentation around the spallation neutron sources – SNS, ESS, J–PARC and Second Target Station at ISIS.

In 2013 the workshop was organized by the Jülich Centre for Neutron Science of the Forschungszentrum Jülich GmbH and was held at the Conference Centre in Ismaning next to Munich on July 2–7, 2013 on the eve of the ICNS–2013 in Edinburg. It carried on the series of Neutron Optics workshops held in Villigen (1999, 2007), Tokyo (2004) and Alpe d'Huez (2010). This time it is also aimed to compliment the International Conference on Neutron Scattering in Edinburgh (ICNS–2013) by providing a platform for detailed discussions on the latest developments in the field of neutron optics.

The scope of the workshop was extended to the neutron detectors (in a way similar to the NOP–2004 held in Tokyo) and was labelled as the International Workshop on Neutron Optics and Detectors, NOP&D–2013. However, in contrast to the Tokyo workshop, the focus of discussions was not the detector technologies (which are the subject of many dedicated meetings), rather than the use of detectors for the purpose of the design of modern instrumentation aiming to inform detector developers about real detectors requirements for new advanced instrumental concepts.

The three–full–days workshop gathered a record number of participants, more than 120, that well exceeded usual numbers (around 70) and even exceeded the limit capacity of the conference hall booked for the workshop! It even forced the organizers to stop the registration before the deadline and to establish a kind of waiting list. Such attendance of scientists representing Australia, Japan, India, Saudi Arabia, Russia, USA, Canada and 10 European countries, actually raised the level of this event from Workshop to Conference.

Discussions at the workshop were devoted but not limited to new concepts in neutron instrumentation, focusing optics, neutron detection in the light of requirements imposed by neutron instruments, neutron polarization and polarization analysis and simulation packages.

The current proceedings are representative of about a half of oral and poster presentations made at the workshop and provide a reader with possibility to outlook the current status and perspectives in the field of neutron optics and related detector developments.

Alexander Ioffe

Editor and Chairman of NOP&D-2013

The additional financial support by ESS Scandinavia, SwissNeutronics, Mirotron, S-DH Heidelberg and ASTRIUM is gratefully acknowledged.

Details of the conference sponsors are available in the pdf.

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

We report on the performance of the first diamond neutron monochromator built at the ILL. It has been designed for the hot neutron diffractometer D9 with the aim of improving significantly the instrument performance in particular for short wavelengths in the 0.3-0.9 Å wavelength range. Diamond crystal plates with dimensions of 1.5 x 1.5 x 0.18 cm³ an average mosaic spread of 0.15° have been synthesized at the University of Augsburg. They exhibited excellent neutron diffraction properties when examined on a neutron double-crystal test setup. Sufficiently thick diamond elements with a controlled mosaic spread of 0.25° have been obtained by stacking several of these crystals. First tests runs carried out at the ILL confirmed the predicted high reflectivity of the diamond stacks. The diamond prototype monochromator uses the (220) reflection in transmission geometry replacing the Cu (220) monochromator on D9 that has the same d-spacing. The final performance studies on D9 showed that the diamond device did not perform better than the original copper crystal. This unexpected result could be explained by significant optical aberrations caused by non- uniformities of both the angular and spatial mosaic distribution in the individual diamond crystals, as revealed by a detailed characterisation study using high-energy X-ray diffraction.

The present study has been conducted in the framework of the channel-cut crystal design for the Kookaburra ultra-small-angle neutron scattering (USANS) instrument to be installed at the OPAL reactor of ANSTO. This facility is based on the classical Bonse-Hart method that uses two multiple-reflection crystal systems. The dynamical theory of diffraction by perfect crystals distinguishes two cases: the Darwin case applying to infinitely thick crystals and the Ewald solution for very small absorption taking into account the reflection from the rear face of a plane-parallel crystal reflecting in Bragg geometry. The former is preferable because it yields narrower rocking curves. To prevent the neutrons to "see" the rear face, grooves were machined into the backside of perfect Si test crystals for single reflection and filled with neutron absorbing material. These samples were examined at the S18 instrument of the Institut Laue-Langevin. Unexpectedly the crystals with empty slots showed an increase of the rocking curve width. When filling the slots with an absorber the widths decreased, but without reaching that of the Darwin curve. Understanding the results and achieving a successful crystal design call for the development of a theory that permits to describe neutron diffraction from crystals with a structured back face.

After preliminary results obtained and published recently [1], in our contribution focusing and reflectivity properties of the dispersive double bent-crystal arrangement are presented in much more detail. It has been found that two different bent perfect crystals in (+n,-m) setting can be good candidates for high efficiency neutron microfocusing as well as high-resolution monochromatisation. Due to the (+n,-m) setting of two different bent perfect crystals, a high resolution is expected in both Δ(2θ (2θ is the scattering angle) as well as Δλ/λ(λ is the neutron wavelength). Experimental tests were carried out with the setting employing the bent Si(111) slab and Si(220)-sandwich, which contained either one, or two or four 1.3 mm thin simply stacked slabs. Thanks to a high reflection probability of both bent elements and an easy manipulation with the curvature of the Si(220)-sandwich, an excellently focused intensive monochromatic beam of the width from one to several millimetres was obtained. The properties of the double bent-crystal setting were studied in Rez at the neutron optics diffractometer for the neutron wavelength of 0.162 nm and for various thicknesses and curvatures of the Si(220)-sandwich. It has been also found that besides an excellent focusing and reflectivity properties of the dispersive double bent-crystal setting the obtained monochromatic neutron current is sufficiently high for standard high-resolution diffraction experiments even at the medium power research reactor.

In this paper studies of neutron diffraction properties of the double crystal (+n,-m) setting containing Si(220) and Si(311) bent perfect crystals (BPC) in symmetric and fully asymmetric diffraction (FAD) geometry with the output beam expansion (OBE), respectively, are presented. Namely, our attention was focused on the properties of the FAD geometry of the BPC Si(311) crystal slab. It has been found that after a beam expansion this FAD geometry can provide a monochromatic beam of a rather large cross-section and of very small divergence with some possible application use.

A substantial fraction of the price for a supermirror neutron guide system is the shielding, which is needed because of the gamma radiation produced as a result of neutron absorption in the supermirror layers. Traditional coatings have been made of nickel-titanium heterostructures, but Ni and Ti also have a fairly high absorption cross section for cold and thermal neutrons. We examine a number of alternatives to Ni as part of a study to reduce the gamma radiation from neutron guides. Materials such as diamond and Be have higher neutron scattering density than Ni, smaller absorption cross section, and when a neutron is absorbed they emit gamma photons with lower energies. We present reflectivity data comparing Ni with Be and preliminary results from diamond coatings showing there use as neutron guide coatings. Calculations show that Be and diamond coatings emit two orders of magnitude fewer gamma photons compared to Ni, mainly because of the lower absorption cross section.

In this work, we present and discuss simulation results for the design of multichannel neutron focusing guides for extreme sample environments. A single focusing guide consists of any number of supermirror-coated curved outer channels surrounding a central channel. Furthermore, a guide is separated into two sections in order to allow for extension into a sample environment. The performance of a guide is evaluated through a Monte-Carlo ray tracing simulation which is further coupled to an optimization algorithm in order to find the best possible guide for a given situation. A number of population-based algorithms have been investigated for this purpose. These include particle-swarm optimization, artificial bee colony, and differential evolution. The performance of each algorithm and preliminary results of the design of a multi-channel neutron focusing guide using these methods are described. We found that a three-channel focusing guide offered the best performance, with a gain factor of 2.4 compared to no focusing guide, for the design scenario investigated in this work.

A multi-channel neutron focusing mirror is a compact device that can effectively enhance neutron intensity because the multi-channel structure can cover a large divergence of a neutron beam. In this study, we attempted to develop a compact multi-channel spheroidal (MS) neutron focusing device for two-dimensional focusing. A prototype of the MS mirror consists of three spheroidal mirrors of different diameters. The mirrors are fabricated through the copper plating method without supermirror coating and are aligned coaxially using ring-shaped spacers. The MS mirror was demonstrated at beam line 10 NOBORU port at J-PARC, which provides neutron beams with time-of-flight spectra. A gain factor of 6 in neutron intensity was obtained over wavelengths greater than 0.5 nm, and an imaging test with sample scanning could be performed with an exposure time of 10 s. A Gd-patterned standard sample was employed and a 2D image with a spatial resolution of 200 μm was successfully obtained.

Elliptic neutron guides are expected to be widely used for construction of long neutron beamlines at the future European Spallation Source and other facilities due to their superiour transmission properties compared to conventional straight guides. At the same time, neutrons traveling long distances are subject to the action of gravity that can significantly modify their flight paths. In this work, the influence of gravity on a neutron beam propagating through elliptic guides is studied for the first time in a systematic way with Monte-Carlo simulations. It is shown that gravity leads to significant distortions of the phase space during propagation through long elliptic guides, but this effect can be recovered by a sufficiently large source size. The results of this analysis should be taken into account during design of long neutron instruments at the ESS and other facilities.

We designed a focus/defocus neutron optics system, in order to investigate the performance, precision, efficiency, and operational and designing challenges of such coupled 2- lens systems, which could potentially find applications where small beam cross sections are beneficial, e.g., virtual neutron source concepts and high efficiency chopper systems. Our particular prototype (as described and discussed in this paper) has already been used in an on-going experiment, involving neutron spin filtering with dynamically polarized protons.

After the designing and construction phases, we continued by performing a long series of simulations and measurements, in order to facilitate the alignment of the lenses, and investigate and understand the behaviour and output of the system. All measurements were performed at the BOA beamline at PSI. The simulations were particularly useful in aligning the lenses: tilts as small as 0.04° could easily be accounted for in our simulations and guide successfully the experimental aligning procedure of the first lens. Although harder to do in the case of two lenses, we were still able to reproduce fairly successfully with our simulations, tilts from both lenses. We have noticed (both in our experiments and simulations) that the sensitivity of such a set-up is ~ 0.01°.

We developed a new neutron mirror made of Diamond-like carbon (DLC). DLC is a film of amorphous carbon that has characteristics of both diamond and graphite. We produced DLC mirrors by ionization deposition method which is one of the chemical vapor deposition (CVD). Generally, DLC made by CVD contents a few tens of percentages of hydrogen. It decreases the Fermi potential of the DLC coating because hydrogen has negative Fermi potential. In order to increase the Fermi potential of the coating, we deuterated the DLC by using deuterated benzene for the source gas. The characteristics of the deuterated DLC(DDLC) coating was evaluated by RBS, ERDA, x-ray reflectivity, AFM. As a result, DDLC coating has 243neV due to deuteration, which is the same level as Ni. The RMS of height of the DDLC was 0.6nm so that the DDLC coating can be applied for a focusing mirror or specular transportation of pulsed neutron. Besides, we also develop Hydrogen/Deuterium DLC multiple layer mirror. So far, 4 layers mirror has been succeeded.

A small-angle neutron scattering instrument using an ellipsoidal focusing mirror has been developed at Hokkaido University and a prototype machine (mfSANS) has been installed at the JRR-3 research reactor at Japan Atomic Energy Agency (JAEA). They are based on an ellipsoidal focusing mirror on a borosilicate glass substrate. It turned out that borosilicate glass was very brittle and difficult to machine or polish it to the required surface-finishing process. In order to improve this situation, we decided to develop a method to create a metal substrate based ellipsoidal focusing mirror. As the first step, test pieces of flat and ellipsoidal surface neutron supermirrors using metal substrates were fabricated. They were first roughly shaped by a conventional numerically controlled (NC) cutting machine and amorphous NiP was plated. They were then machined using an ultrahigh precision cutting (UPC) method and finished by NC polishing techniques. Surface roughness of R_a ≈ 0.78 nm and surface figure error of submicrometer were realized so far.

In order to efficiently execute neutron beam experiments at JRR-3, the number of beam ports was increased and neutron beam instruments were rearranged in the C2 cold neutron beam line by using a newly developed compact vertical splitting system. Considering the space available for instruments at the downstream region of the cold neutron beam line, the deflection angles of the compact vertical splitting system were set as 10° and 20°. To branch off the cold neutron beam, a bender with characteristic wavelength of 4 Å was developed using Ni/Ti supermirrors coated on both sides of 0.2-mm-thickness silicon substrates. The channel width of the bender is 0.2 mm. The radius of curvature of the compact bender is 938 mm and the lengths of the benders are 160mm and 320 mm, yielding deflection angles of 10° and 20°, respectively. Neutron flux at the end of the neutron guide installed at the bender exit, the deflection angle of which is 20°, was measured to be 1.58 x10⁷ n·cm⁻²·s⁻¹ with a gold foil activation method. We found that the measured flux agrees with the simulated value.

Modern spallation neutron sources are driven by proton beams ~ GeV energies. Whereas low energy particle background shielding is well understood for reactors sources of neutrons (~20 MeV), for high energies (100s MeV to multiple GeV) there is potential to improve shielding solutions and reduce instrument backgrounds significantly. We present initial measured data on high energy particle backgrounds, which illustrate the results of particle showers caused by high energy particles from spallation neutron sources. We use detailed physics models of different materials to identify new shielding solutions for such neutron sources, including laminated layers of multiple materials. In addition to the steel and concrete, which are used traditionally, we introduce some other options that are new to the neutron scattering community, among which there are copper alloys as used in hadronic calorimeters in high energy physics laboratories. These concepts have very attractive energy absorption characteristics, and simulations predict that the background suppression could be improved by one or two orders of magnitude. These solutions are expected to be great benefit to the European Spallation Source, where the majority of instruments are potentially affected by high energy backgrounds, as well as to existing spallation sources.

A ³He neutron spin filter (NSF) program for polarized neutron scattering was launched in 2006 as part of the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR) Expansion Initiative. The goal of the project was to enhance the NCNR polarized neutron measurement capabilities. Benefitting from more than a decade's development of spin-exchange optical pumping (SEOP) at NIST, we planned to employ SEOP based ³He neutron spin filters for the polarized neutron scattering community. These ³He NSF devices were planned for use on different classes of polarized neutron instrumentation at the NCNR, including triple-axis spectrometers (TAS), small-angle neutron scattering instruments (SANS), reflectometers, and wide-angle polarization analysis. Among them, the BT-7 thermal TAS, NG-3 SANS, and MAGIK reflectometer have already been in the user program for routine polarized beam experiments. Wide-angle polarization analysis on Multi-Axis Crystal Spectrometer (MACS) has been developed for user experiments. We describe briefly the SEOP systems dedicated for polarized beam experiments and polarizing neutron development for each instrument class. We summarize the current status and polarized neutronic performance for each instrument. We present a ³He NSF hardware and software interface to allow for synchronization of ³He polarization inversion (neutron spin flipping) and free-induction decay (FID) nuclear magnetic resonance (NMR) measurements with neutron data collection.

In order to produce high-quality ³He Neutron Spin Filters (NSF) with a high polarisation level, it is necessary to achieve a long ³He relaxation time by the reduction of the wall relaxation. This requires one to minimise the amount of impurities at the surface of the glass cells, and to have as few contaminants as possible in the gas filling system. In this report we describe the detailed procedure we employ to produce ³He cells using our newly built filling station. The obtained life times for a number of cells are practically approaching the fundamental limit imposed by the dipole-dipole interaction between ³He atoms.

In order to expand the measurable neutron energy range up to the energy of epithermal neutrons in polarized neutron experiments, a portable polarized ³He neutron spin filter (NSF) was developed in the Materials and Life science experimental Facility (MLF) at J- PARC. After the generation of ³He polarization through a spin exchange optical pumping method, the NSF was used as a neutron spin polarizer and flipper in a beam line. We constructed a simple neutron spin analysis apparatus with two ³He NSFs and made a preliminary attempt to visualize magnetic fields generated by a coil. The results represented that our apparatus could function for neutron wavelengths between approximately 0.5-5 Å through the use of a neutron time-of-flight method.

We present a status of recent projects involving the in-house production of neutron multilayer optics, mainly polarizing supermirrors, at the ILL. Our main "mass production" project is for the wide-solid angle analyzing benders for the future instrument WASP (Wide Angle Spin Echo). The current status of this project based on Co/Ti supermirrors, which spans several years, will be presented. Some parameters of polarizing supermirrors for cavity polarizers, mainly based on Fe/Si supermirrors and produced in the past few years for various ILL instruments, are also reported. Some supermirror samples produced in order to study depolarization effects are also mentioned.

We present progress towards a complete system for neutron polarization analysis on a time-of-flight (TOF) neutron spectrometer with a large area/angle detector array. Finite element calculations have been used to model the field gradients of a newly proposed PASTIS coil set, which uses a wide-angle banana shaped ³He Neutron Spin Filter cell (NSF) to cover a large neutron scattering solid angle. The final goal of this insert is to enable X-Y-Z polarization analysis to be installed on the future hot/thermal time-of flight spectrometers, although the method is also applicable to thermal/cold spectrometers as well. The components of this system, such as the magnetic field coils and design are applicable to neutron spectroscopy with wide angle detector arrays in general, and the ³He wide angle cell developments for polarized inelastic neutron scattering are independent from the methods used to polarize the gas as well.

The successful use of ³He cells in polarized neutron applications demands that once polarized the gas has both a long relaxation time and high polarization. In spin-exchange optical pumping the cell characteristics determine the maximum polarization as well as the lifetime.

We report on our experience of neutron spin filter cells, showing results on the orientation dependence of such cells. We observe a previously observed lifetime hysterisis effect in ³He cell relaxation lifetime and include new measurements of the angular dependence of the relaxation lifetime, that are characteristic of a dipolar effect which diminishes upon repeated pumping/cooling cycles. We present demonstrations of magnetization effects in ³He and ¹²⁹Xe cells and show the applicability of using sol-gel coatings on reducing the magnetization effect in ¹²⁹Xe cells.

We report recent results of the stability of the polarization in new SEOP cells, which was evident for 2 states, one with high energy spin state, low T₁ orientation and the second with low energy spin state, high T₁ orientation. These results are suggestive of an abnormal relaxation and have only been observed for cells with short (T₁ <10 Hours) lifetimes.

A new neutron reflectometer, SHARAKU, with a vertical sample-plane geometry was installed at beam line 17 at J-PARC Materials and Life Science Facility. Although a polarizing supermirror was previously installed as a neutron spin analyzer on SHARAKU, a ³He spin filter is advantageous because it can cover a large solid angle. An in-situ SEOP ³He spin filter system using a new compact laser unit has been developed for the analyzer. In this paper, we report a successful off-specular measurement with the new compact in-situ SEOP analyzer at SHARAKU.

We describe here a new type of wide-angle supermirror-based multichannel analyzer configured in the fan orientation. The increased channel width allows for reflections only from one of the channel's walls, so that the overlap of beams propagating through neighboring channels is avoided. However the straight beam, which is unavoidably propagating through the channels with the increased width, is blocked by an absorbing mask at the entrance of the analyzer. The neutron transmission of such analyzer is 22% higher and the number of the supermirrors needed to cover the same beam cross section is 16% less in comparison with a conventional fan analyzer. Results of the calculations and first tests of the analyzer at the Magnetism Reflectometer at Oak Ridge National Laboratory, USA, are presented.

The use of polarized protons as neutron spin filter is an attractive alternative to the well established neutron polarization techniques. The spin-dependent neutron scattering cross section of protons is usefully large up to the sub-Mev region. Employing optically excited triplet states for the dynamic nuclear polarization (DNP) of the protons, low temperatures and strong magnetic fields are not required and the apparatus can be simplified.

The triplet DNP method can be used to build a reliably working neutron spin filter that is operated in 0.3T and about 100 K. The high proton polarization of 0.5 obtained is presently still limited by the cooling of the sample. The corresponding analyzing power of A ~ 0.5, obtained with the 5 mm thick sample, can be further increased using a longer sample. Interesting possibilities for a triplet spin filter are opened by the use of neutron optics elements that allow to adapt the beam to the filter cross section.

A number of basic elements for neutron spin manipulation optics (NSMO) based on Larmor and non-Larmor (quantum) precessions under reflection are considered. It is concluded that transition to 3D in neutron polarization optics may bring additional instrumental possibilities. New neutron optical devices will include spin turners (particularly, π/2-turners and π- turners, or flippers), spin precessors and antiprecessors, 3D-polarizers, 3D-analyzers, 3D- rotators, spin manipulators, hyper-polarizers. The innovative neutron optics is directly applicable to developing 3D polarization and polarimetry techniques, such as reflectometry with 3D- polarimetry, Neutron optical Spin Echo (NoSE), including compact NoSE and TOF NoSE schemes. A hyper-polarizer is a device which not only separates neutrons with the opposite spins, but also flips the 'wrong' spins. Thus, hyper-polarizers can double the intensity of polarized neutron beams, although a gain in the intensity can be achieved only with the increase either in the angular divergence or in the width of the beam, in full accordance with the Liouville theorem. The tasks to be solved for implementation of the NSMO concepts are discussed.

The Meissner effect in a thin-film superconductor can be used to create a sharp boundary between regions of different magnetic field and hence can be used as a component of neutron spin manipulation devices. We have developed two cryogenic neutron spin manipulation devices using single-crystal, high-T_c, YBCO films, which can be cooled without using liquid cryogens and eliminate small angle scattering associated with polycrystalline films.

The devices are a spin flipper and a spin precession device both of which use 350-nm-thick YBCO films covered with gold on a 0.5 mm thick sapphire substrate. The spin flipper consists of one such film mounted on an oxygen-free copper frame and connected to a closed-cycle He refrigerator. The flipper is capable of working with a maximum neutron beam size of 42 x 42 mm² and can be used with both vertical and horizontal guide fields.

The spin precession device was constructed by mounting two of the YBCO films parallel to one another with an H-magnet between them. By changing the current through the H – magnet, the precession of the neutron polarisation between the films can be controlled. Tests at the Low Energy Neutron Source (LENS) show that this device is capable of generating controlled spin precession for a neutron beam up to 20 x 20 mm² in cross section.

Grazing Incidence Neutron Spin Echo Spectroscopy (GINSES) opens new possibilities for observing the thermally driven dynamics of macromolecules close to a rigid interface. The information about the dynamics can be retrieved as a function of scattering depth of the evanescent neutron wave, on the length scale in the range of some 10-100 nm. Using a classical neutron spin echo spectrometer with a laterally collimated beam, dynamics can be measured in grazing incidence geometry. We show examples of how the interface modifies the dynamics of microemulsions, membranes and microgels. Instrumental details and possible improvements for this technique will be presented. The key issue is the low intensity for dynamics measurements with an evanescent neutron wave. Conceptual questions how a specialised instrument could improve the experimental technique will be discussed.

The Bragg Institute is operating the neutron scattering science facilities at the Australian research reactor OPAL. The first set of seven neutron scattering instruments was provided as part of the OPAL construction project which was completed in 2007. During the period 2008 – 2013, the instrument suite was significantly expanded by a further seven instruments. In addition to this, major investments were made to establish a world-class infrastructure for supporting these instruments, including new sample environments, ³He polarisers/analysers, additional neutron guides and a Be filter option for chemical spectroscopy.

The progress in neutron delivery systems and in neutron focusing techniques has made possible neutron studies of excitations in sub-cm³-sized single crystals, which are still much larger than crystal sizes needed for standard laboratory characterization techniques. In an effort to further reduce this gap we are proposing the exTAS project, which intends to stimulate a paradigm shift towards the use of mm³-sized samples in neutron spectroscopy. The exTAS project aims to boost the TAS sensitivity limits by combining sharp mm-sized focal spots, minimizing penumbra effects in sample environment illumination, with a spectrometer layout downscaled to a tabletop size and enclosed in a shielding casemate. The reduced spectrometer dimensions will provide enhanced flexibility in adapting the momentum resolution to the problem being studied and will facilitate the sub-millimetre positioning accuracy of its components, matching the reduced focal spot size.

The utilization of X-rays for material research is common in many respects since their discovery at the end of the 19th century. New sources as electron synchrotrons or free-electron lasers push the methodology and the application ranges further. A similar approach started 50 years later with neutrons when sources with reasonable high intensity became available.

Today, there are many similarities and complementarities visible between X-ray and neutron studies and the involved techniques. Therefore, it is worth to compare and to adapt from the advanced X-ray techniques and to translate it into the neutron world. Despite of the lack of neutron intensities compared to the most brilliant X-ray beams, the specific properties of neutrons (contrast, spin, magnetic moment, penetration power) are utilized and they will further play an important role in non-invasive studies on the micro- and macro scale.

This paper wants to encourage to "look over the fence" into activities of the X-ray community as currently running in the COST action MP-1203.

The Goos-Hanchen effect, a longitudinal shift of a wave beam at total inner reflection, is a well-known optical phenomenon. It was discovered in 1947 and have been observed many times at reflection of micro- and ultrasonic waves since then. Here we present an elementary theory of the GH. effect to describe reflection of a massive particle and demonstrate how the shift is related to delay time at reflection. It is shown that giant positive or negative longitudinal shifts of the neutron beam may occur at neutron reflection from some specially manufactured planar system. The possibility of delay time measurement at neutron reflection and direct experimental observation of the GH shift are also discussed.

Ultracold neutrons (UCNs) are neutrons whose kinetic energy is around a few hundred nanoelectronvolts. Neutrons with such small kinetic energy can be trapped in a material vessel or magnetic fields. Because of these unique characteristics, UCNs are used for some important experiments of fundamental physics. The Doppler shifter is a device to produce UCN by slowing them down by the reflection on a mirror moving with half of the velocity of incoming neutrons. A Doppler shifter using a quadruple-stack of monochromatic supermirrors that reflects neutrons with a velocity around 68m/s [1, Hino et al.(2010)] was fabricated, and operated with a pulsed neutron source of J-PARC. An important feature of the Doppler shifter is the use of a pulsed neutron beam. Unlike in continuous neutron beams, the neutron velocity can be selected by choosing a time slice in a pulsed neutron bunch. Thus the UCN production improves by ~80 times in the case of J-PARC. We successfully produced the UCNs by the Doppler shifter: the measured UCN production rate is consistent with the simulations.

The neutron electric dipole moment (nEDM) is sensitive to new physics beyond the standard model and could prove to be a new source of CP violation. Several experiments are being planned worldwide for its high-precision measurement. The nEDM is measured as the ultracold neutron (UCN) spin precession in a storage bottle under homogeneous electric and magnetic fields. In nEDM measurement, the systematic uncertainties are due to the motion of the UCNs, the geometry of the measurement system, and inhomogeneous electric and magnetic fields. Therefore, it is essential to quantitatively understand these effects in order to reduce them. Geant4UCN is an ideal simulation framework because it can compute the UCN trajectory, evaluate the time evolution of the spin precession due to arbitrary electric and magnetic fields, and define the storage geometry flexibly. We checked how accurately Geant4UCN can calculate the spin precession. We found that because of rounding errors, it cannot simulate it accurately enough for nEDM experiments, assuming homogeneous electric and magnetic fields with strengths of 10 kV/cm and 1 μT, respectively, and 100 s of storage. In this paper, we report on its discrepancies and describe a solution.

Recently, an interface between the Monte Carlo code MCNPX and the neutron ray-tracing code MCNPX was developed [1, 2]. Based on the expected neutronic performance and guide geometries relevant for the ESS, the combined MCNPX-McStas code is used to calculate dose rates along neutron beam guides. The generation and moderation of neutrons is simulated using a full scale MCNPX model of the ESS target monolith. Upon entering the neutron beam extraction region, the individual neutron states are handed to McStas via the MCNPX-McStas interface. McStas transports the neutrons through the beam guide, and by using newly developed event logging capability, the neutron state parameters corresponding to un-reflected neutrons are recorded at each scattering. This information is handed back to MCNPX where it serves as neutron source input for a second MCNPX simulation. This simulation enables calculation of dose rates in the vicinity of the guide. In addition the logging mechanism is employed to record the scatterings along the guides which is exploited to simulate the supermirror quality requirements (i.e. m-values) needed at different positions along the beam guide to transport neutrons in the same guide/source setup.

Latest developments of the polarized neutron suite in the VITESS simulation package allowed for simulations of time-dependent spin handling devices (e.g. radio-frequency (RF) flippers, adiabatic gradient RF-flippers) and the instrumentation built upon them (NRSE, SESANS, MIEZE, etc.). However, till now the magnetic field distribution in such devices have been considered as "ideal" (sinusoidal, triangular or rectangular), when the main practical interest is in the use of arbitrary magnetic field distributions (either obtained by the field mapping or by FEM calculations) that may significantly influence the performance of real polarized neutron instruments and is the key issue in the practical use of the simulation packages. Here we describe modified VITESS modules opening the possibility to load the magnetic field 3-dimensional space map from an external source (file). Such a map can be either obtained by direct measurements or calculated by dedicated FEM programs (such as ANSYS, MagNet, Maxwell or similar). The successful use of these new modules is demonstrated by a very good agreement of neutron polarimetric experiments with performance of the spin turner with rotating magnetic field and an adiabatic gradient RF-flipper simulated by VITESS using calculated 3-dimensional field maps (using MagNet) and magnetic field mapping, respectively.

We present a newly-developed open-source software toolkit for handling and analysing the 4-dimensional datasets generated by modern multi-layer time-of-flight (TOF) position-sensitive detectors (PSD). Two such detectors of the type "Cascade" are in operation at the MIEZE beam line MIRA 2 and at the neutron resonance spin-echo spectrometer RESEDA at FRM II. The software consists of several modules for data analysis and instrument parameter calculations to assist the user during experiments, during simulations and in data evaluation. Specifically for the Cascade detector, it contains modules that correct phase-shifts in the MIEZE signal caused by the detector geometry and layout.

The McStas neutron ray-tracing software package is a versatile tool for building accurate simulators of neutron scattering instruments at reactors, short- and long-pulsed spallation sources such as the European Spallation Source. McStas is extensively used for design and optimization of instruments, virtual experiments, data analysis and user training. McStas was founded as a scientific, open-source collaborative code in 1997.

This contribution presents the project at its current state and gives an overview of the main new developments in McStas 2.0 (December 2012) and McStas 2.1 (expected fall 2013), including many new components, component parameter uniformisation, partial loss of backward compatibility, updated source brilliance descriptions, developments toward new tools and user interfaces, web interfaces and a new method for estimating beam losses and background from neutron optics.

VITESS is a software widely used for simulation of neutron scattering experiments. Although originally motivated by instrument design for the European Spallation Source, all major neutron sources are available. Existing as well as future instruments on reactor or spallation sources can be designed and optimized, or simulated in a virtual experiment to prepare a measurement, including basic data evaluation. This note gives an overview of the VITESS software concept and usage. New developments are presented, including a 3D visualization of instruments and neutron trajectories, a numerical optimization routine and a parallelization tool allowing to split VITESS simulations on a computer cluster.

Various neutron scattering instruments at Dhruva reactor, BARC, are equipped with indigenously developed neutron detectors. Range of detectors includes proportional counters, beam monitors and linear position sensitive detectors (PSD). One of the instruments is recently upgraded with multi-PSD system of high efficiency and high resolution PSDs arranged in stacking geometry. These efforts have resulted in improving the throughput of the instrument and reducing experiment time. Global scarcity of ³He has made essential to explore other options like BF³ gas and ¹⁰B coatings.

PSDs with coaxial geometry using BF³ gas and ¹⁰B coating (90% enriched) are fabricated and characterized successfully. These PSDs are used as the alternative to ³He PSD in equivalent geometry. Though efficiency of PSDs in similar dimensions is lower than that with ³He, these large numbers of PSDs can be arranged in multi-PSD system. The PSD design is optimized for reasonable efficiency. An array of 60 BF³ filled PSDs (1 m long) is under development for the Time of Flight Instrument at Dhruva. Further improvement in efficiency can be obtained with novel designs with complex anode-cathode geometry. Various challenges arise for long term operation of PSDs with BF³ gas, in addition to complexity of data acquisition electronics. Study of gas aging with detector fabrication materials has been carried out. PSDs with ¹⁰B coating show advantage of non toxic nature but have low efficiency. Multiple ¹⁰B layers intercepting neutron beam are used to increase the efficiency. PSD designed with small anode- cathode spacing and array of multiwire grids placed between double sided ¹⁰B coated plates are being fabricated. Assembly is arranged in curvilinear geometry with zero parallax. Overview of these developments is presented.

We investigate the possibility of using the prompt γ rays emitted by aluminum windows in order to monitor the neutron flux of the beam. A Nal scintillation detector is used to detect the prompt γ rays. No additional material apart from the unavoidable Al windows along the flight path is placed in the beam. The performance of the monitor is compared to that of a standard BF3-monitor placed in the beam. Influences of a magnetic field on the photomultiplier of the Nal monitor is discussed, as well as the influence of activation gammas. At an instrument using a beam chopper the time behaviour is discussed.

Neutron beam monitors are regularly used in various neutron beam experiments to compare two or more sets of data taken in different experimental conditions. A neutron lifetime experiment at BL05, the NOP beamline, in J-PARC requires to monitor the initial neutron intensity with an precision of 0.1% to measure the neutron lifetime with the same accuracy. The performance of a thin ³He gas neutron beam monitor used for the experiment was studied to estimate the systematic uncertainties in the neutron lifetime measurement.

A neutron detector concept based on solid layers of boron carbide enriched in ¹⁰B has been in development for the last few years as an alternative for ³He by collaboration between the ILL, ESS and Linköping University. This Multi-Grid detector uses layers of aluminum substrates coated with ¹⁰B₄C on both sides that are traversed by the incoming neutrons. Detection is achieved using a gas counter readout principle. By segmenting the substrate and using multiple anode wires, the detector is made inherently position sensitive. This development is aimed primarily at neutron scattering instruments with large detector areas, such as time-of-flight chopper spectrometers. The most recent prototype has been built to be interchangeable with the ³He detectors of IN6 at ILL. The ¹⁰B detector has an active area of 32 x 48cm². It was installed at the IN6 instrument and operated for several weeks, collecting data in parallel with the regularly scheduled experiments, thus providing the first side-by-side comparison with the conventional ³He detectors. Results include an efficiency comparison, assessment of the in-detector scattering contribution, sensitivity to gamma-rays and the signal-to-noise ratio in time-of-flight spectra. The good expected performance has been confirmed with the exception of an unexpected background count rate. This has been identified as natural alpha activity in aluminum. New convertor substrates are under study to eliminate this source of background.

A thermal neutron detector based on ZnS(Ag)/⁶LiF scintillator, wavelength- shifting fibers (WLS) and silicon photomultipliers (SiPM) is under development at the Paul Scherrer Institute (PSI) for upgrading the POLDI instrument, a pulse-overlap diffractometer. The design of the detector is outlined, and the measurements performed on a single channel prototype are presented. An innovative signal processing system based on a photon counting approach is under development. Its principle of operation is described and its performances are evaluated on the basis of a Monte Carlo simulation.

A wavelength-shifting-fibre-based scintillator detector has been developed as an alternative detector to ³He gas. The detector is intended for use in an inelastic neutronscattering instrument at J-PARC. The detector being developed, which is based on the one made for a SENJU diffractometer, is designed to cover a large scattering angle with a moderate pixel size as well as exhibiting a high detection efficiency, low gamma-ray sensitivity and low background count rate. A prototype detector with a pixel size of 20 x 20 mm and a neutron- sensitive area of 320 x 320 mm² has been constructed. This paper describes the design of the detector and its performance relative to the original SENJU detector.

A low-afterglow, ¹⁰B-doped neutron-sensitive ZnS/¹⁰B₂O₃ scintillator was developed. The developed ZnS phosphor has a primary decay time constant of about 60 ns with a low afterglow. The developed scintillator exhibited a mean afterglow height of 4% relative to the peak at 1 μs after the peak, which is half that of a commercial ZnS/⁶LiF scintillator manufactured by Applied Scintillation Technologies. The count-rate capability of a wavelength-shifting-fibre-based detector was increased to 30,000 cps by implementing the developed scintillator from 5,000 cps with the commercial scintillator.

Multiwire counters are likely to remain a reliable and cost-efficient option for a large class of instruments. Delay-line position encoding is widely used in multiwire position sensitive particle detectors. Improvement of several detector parameters is a continuous demand such as count rate or position resolution. Digitization of the analog detector signals retains all information about the detected events at the highest count rate. Neutronic measurement results on our standard detector with 200mm × 200mm active area are presented with different acquisition algorithms. The analog signals were digitized by a high speed, multichannel Acqiris digitizer with 1 ns sampling resolution.

A multiwire proportional chamber (MWPC) neutron detector system was developed for the Materials and Life Science Experimental Facility at the Japan Proton Accelerator Research Complex. Its basic performance was evaluated by an irradiation experiment using a Cf-252 neutron source. A short response time and high spatial resolution can be obtained using an individual line readout method. The detector system exhibited a one-dimensional uniformity of response of 4.8% and 3.8% in the x- and y-directions, respectively. The uniformity of all pixels in the two-dimensional image was 7.9%. The average intrinsic spatial resolution was 1.55 mm full width at half maximum in the sensitive region calculated by taking into account the track lengths of secondary particles. The signal intensity of the system remained constant during the operation for 500 min under Cf-252 neutron irradiation.