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Neutron reflectometry is a powerful tool to investigate chemical and magnetic depth profiles near surfaces. The advantages of neutrons compared to x-rays are their sensitivity to isotopes, the high penetration capabilities and the high sensitivity to magnetic induction. The biggest disadvantage however is the low flux available, which leads to much longer counting times on much larger samples. In order to boost the performance of neutron reflectometers, a focusing guide system was developed and realised over recent years. Here we report on the application and performance of a down-scaled demonstrator of such a Selene guide, installed as an add-on on the time-of-flight (TOF) reflectometer Amor at the PSI. Due to the limited size of the guide, the flux is concentrated to a footprint of at most 2 mm width. It is thus possible to avoid illumination of contacts even on small samples. Despite the fact that typical samples measured on Amor with a size of 10 × 10 mm 2 are markedly under illuminated, the presented set-up leads to a reduction in counting time of 80%. The use of the demonstrator thus allows for in-situ or in-operando investigations with a time resolution of a few minutes for a q z range from 0.005 Å − 1 to 0.08 Å − 1 . Besides a short recapitulation of the concept of focusing reflectometry, a detailed description of the data reduction and its quality is given, followed by an application example. [ABSTRACT FROM AUTHOR]

Abstract: We have designed and built a parabolically shaped reflector with a Ni/Ti-multilayer coating, graded along the length of the device. The bilayer thickness follows the varying angle of incidence to match the Bragg condition for a beam parallel to the axis of the parabola. As measurements show, this concept leads to a higher reflectivity for monochromatic neutrons compared to a conventional supermirror coating. With a reflectivity we measured a gain of 5 when focusing a 8.6mm wide beam of divergence down to 1.6mm. The wavelength band was and the focal point was 250mm behind the device. [Copyright &y& Elsevier]

The high brilliance at the European Spallation Source (ESS) will allow for performing experiments with much smaller samples than at present neutron facilities and in much more complex sample environments. However the higher flux also results in higher background from unwanted neutrons not originating from scattering of the sample. We here present a new design idea for beam delivery, where a 165 m ballistic guide system with good transport properties is followed by a 4–8 m SELENE guide system similar to Montel optics used for X-ray optics. We have investigated the system by detailed Monte-Carlo simulations using McStas. We show that under certain conditions, this set-up works surprisingly well, with a brilliance transfer of 20–60% for neutrons of wavelength 4 Å and above. We demonstrate that the guide system is able to focus the beam almost perfectly onto samples sizes in the range of 0.1–2 mm. We furthermore show that our SELENE system is insensitive to gravity and to realistic values of guide waviness. We argue that this guide system can be useful as an optional guide insert when small samples are used in the vicinity of bulky sample environment, e.g. for high-field or high-pressure experiments. [ABSTRACT FROM AUTHOR]

Abstract: In various fields of neutron scattering there is a tendency to use smaller and smaller samples. There are various reasons for this, e.g. the limited size in high pressure cells, the restrictions given by growth methods of thin films, or the impossibility to grow larger single crystals. With conventional guides this leads to the situation that a white beam with some 50cm2 cross-section and a broad divergence is to illuminate a sample of some mm2 area. Thus more than 99% of the neutrons leaving the guide are not needed and cause background and radiation problems. It is suggested to change the order of the optical elements and the design of the guide section to filter neutrons not intended to hit the sample as early as possible. As an example a set-up for specular reflectivity on small samples is presented. A double monochromator some meters behind the source cuts away all neutrons of the wrong wavelength even before they enter the guide. The guide itself is one branch of an ellipse. It maps the divergent beam from the monochromator to a convergent beam at the sample position. An entry aperture at the first focal point, a bit larger than the sample, guarantees that just enough neutrons enter the guide to bath the sample. There is no direct line of sight to the source and the guide ends far away from the sample position, so that there are only few spacial restrictions. Detailed McStas calculations and a design study for a down-scaled test device, both for reflectometry and diffraction, are presented. [Copyright &y& Elsevier]

We demonstrate a stationary helium gas density gradient which is needed for a proposed novel low-energy μ + beam line. In a closed system with constant pressure the corresponding density gradient is only a function of the temperature. In a neutron radiography experiment two gas cells with different geometries were filled with 3 He gas at constant pressures of about 10 mbar. Temperatures in the range from 6 K to 40 K were applied and density distributions with a maximum to minimum density ratio of larger than 3 were realized. The distribution was investigated employing the strongly neutron absorbing isotope 3 He. A simple one-dimensional approach derived from Fourier׳s law describes the obtained gas density with a deviation < 2 % . [ABSTRACT FROM AUTHOR]

In view of the trend towards smaller samples and experiments under extreme conditions it is important to deliver small and homogeneous neutron beams to the sample area. For this purpose, elliptic and/or Montel mirrors are ideally suited as the phase space of the neutrons can be defined far away from the sample. Therefore, only the useful neutrons will arrive at the sample position leading to a very low background. We demonstrate the ease of designing neutron transport systems using simple numeric tools, which are verified using Monte-Carlo simulations that allow taking into account effects of gravity and finite beam size. It is shown that a significant part of the brilliance can be transferred from the moderator to the sample. Our results may have a serious impact on the design of instruments at spallation sources such as the European Spallation Source (ESS) in Lund, Sweden. [ABSTRACT FROM AUTHOR]

Abstract: A transmission neutron polariser (Fe/Si supermirror) has been successfully implemented in the small angle neutron scattering instrument SANS-I at the SINQ neutron source. The polariser is needed for investigations of magnetic nanostructures as well as for spin contrast variation techniques relying on the spin-dependent neutron scattering length of polarised nuclei. The V-shaped polariser is installed in the first section of the collimator system of the SANS instrument and its performance is optimised for neutrons with a wavelength between 0.5 and 1.0nm. For a precise polarisation analysis of a beam with selectable incident divergence, such as in SANS experiments, an opaque spin filter is ideal. We used a solid polarised proton target exploiting the strong spin-dependent neutron scattering cross-section of hydrogen and determined the neutron beam polarisation to a precision of for different collimations in a broad wavelength band. [Copyright &y& Elsevier]

Abstract: We have investigated the focusing properties of the prototype of a transportable elliptic neutron guide. We demonstrate that the elliptic guide allows to map a point-like neutron source in one focal point on a tiny spot in the other focal point. We also show that an elliptically tapered neutron guide increases the neutron flux density in the focal point by at least one order of magnitude compared to the flux density of the original neutron beam. This allows to use neutron beams more efficiently in experiments with small samples. We used the elliptic neutron guide to focus a several centimeters wide neutron beam on a tiny sample with the dimensions and easily detected the ordered moment of this antiferromagnetic insulator. This suggests that many more small samples, in particular in high pressure experiments, can be studied with elliptic neutron guides. [Copyright &y& Elsevier]

Abstract: A new high resolution (400nm) Fresnel Zone Plate (ZP) of 1mm diameter has been designed and produced in order to accurately measure its spatial resolution and efficiency. This experiment is an extension of the previous tests performed to measure the efficiency of these devices. The measurements were carried out on the diffractometer Morpheus at PSI using a new ZP designed to obtain a small focal length of 0.833 m at 4.7Å. In this experiment a 0.8mm edge square neutron source at 4.7Åwas demagnified by the ZP by a factor 2 down to about 0.4mm at 1.24m distance from the ZP. With this configuration, using a Gd knife edge, we determined the transverse profile of the image with a spatial accuracy of 0.01mm. In addition an appropriate configuration was used to measure the efficiency of the ZP, which was equal to , to be compared to 0.325, that is the ideal value at 4.7Å. The result for the ZP resolution suggests that the image has a broadening in the range of 0.01mm, corresponding to an effective wave front coherence over a distance greater than , to be compared to some as deduced from the indetermination principle, according to the beam divergence. Numerical simulations of the ZP are performed with a partially coherent wave front to show the effect of the phase variation on the intensity at different positions. [Copyright &y& Elsevier]

Abstract: Nickel/titanium multilayers (ML) and supermirrors (SM) were fabricated by DC magnetron sputtering on glass or Si (100) substrates. It was possible to increase the reflectivity of ML and SM by the deposition of an ultrathin Cr layer at the Ni/Ti interfaces. Interdiffusion decreases when the Ni and Ti are separated by a covering Cr layer (3Å), whereas, in the range where the Cr interlayer thickness is higher than the Ni/Ti interdiffusion depth (approximately 6Å) or the surface roughness, the growth of a closed Cr layer is prohibited reducing the reflectivity. The presence of a 10Å Cr interlayer on some Ti layers also results in enhanced reflectivities due to a smoothing effect of the interface for the following layers. The reflectivities of two monochromators for and a bandwidth (Δλ/λ) of 6% and 12% reach a value of approximately 0.90. [Copyright &y& Elsevier]