Proceedings Volume 1738

Neutron Optical Devices and Applications

Charles F. Majkrzak, James L. Wood
cover
Proceedings Volume 1738

Neutron Optical Devices and Applications

Charles F. Majkrzak, James L. Wood
View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 23 November 1992
Contents: 10 Sessions, 48 Papers, 0 Presentations
Conference: San Diego '92 1992
Volume Number: 1738

Table of Contents

icon_mobile_dropdown

Table of Contents

All links to SPIE Proceedings will open in the SPIE Digital Library. external link icon
View Session icon_mobile_dropdown
  • Introductory Presentation
  • Polarized Beams
  • Multilayer Characterization
  • Multilayer Monochromators
  • Reflectometry: Applications
  • Reflectometry: Analysis
  • Reflectometry and Microscopy: Instruments
  • Neutron Focusing
  • Crystal Diffraction Optics
  • Section
  • Multilayer Characterization
  • Section
Introductory Presentation
icon_mobile_dropdown
Neutron optics at the Advanced Neutron Source (Invited Paper)
John B. Hayter
The Advanced Neutron Source (ANS), currently in conceptual design at Oak Ridge National Laboratory, will be a multipurpose neutron research laboratory serving the needs of academic and industrial users throughout the nation in chemistry, biology, physics, materials science, and many other fields. It will be centered on the world's highest flux neutron beam reactor, but that is only the starting point for ensuring high productivity, which will be enhanced further by careful design of the neutron beam delivery systems. Many instruments will be situated in low backgrounds at distances up to 80 m from the reactor, using neutron guides with tailored neutron optical coatings for beam transport. Where appropriate, multilayer optical coatings will also be used in beam focussing (and sometimes defocussing) devices. Certain applications, such as prompt-(gamma) activation analysis, may also use neutron fiber optics to split beams between multiple samples. Neutron optical techniques such as interferometry and reflectometry will form a basic part of the research instrument complement at the ANS. Finally, very long wavelength neutron beams, in which the optical potential becomes very large, will be provided for specialized research.
Improvement in the synthesis of Ni/Ti neutron mirrors
Alan F. Jankowski
Improvement in the as-deposited structure of Ni/Ti multilayers is achieved through optimization of the sputter deposition process. In the as-deposited condition, these Ni/Ti multilayers are well suited for very high reflectivity (> 95%) neutron supermirror application. Smooth layering is produced with compositionally abrupt interfaces yielding an effective roughness less than 1 nm. The deposition parameters are controlled to produce a near thermalized condition for the sputtered neutrals. The Ni/Ti multilayer system is not structurally stable, however, when subject to moderate heating (> 300 degree(s)C) or irradiation. The in-use degradation of interface structure from neutron irradiation may be limitation for the Ni/Ti system.
Status of supermirror research at OSMC
The need for increased neutron flux at government and university neutron scattering facilities has created a significant demand for multilayer coated surfaces with a maximum reflectivity and extension of critical angle. OSMC's progress in the development of high quality (NiC)-Ti and Fe-Si supermirrors is presented. Factors involved in the optimization of reflectivity and critical angle are discussed.
Reflectivity improvements for neutron mirrors and supermirrors
Bernard Vidal, Z. Jiang, Francois J. Samuel
In order to study multilayers for neutrons optics, Ni/Ti multilayers were first realized by magnetron sputtering technique on super-polished Si wafer and Borkron glasses. Including carbon in the nickel target in order to improve neutron reflectivity, nickel carbide/titanium multilayers were deposited under the same conditions. The neutron optical quality of NiC/Ti multilayers are better than Ni/Ti stacks. The grazing angle neutron reflectivity results were subsequently confirmed by other techniques. X-ray diffraction measurements show a nickel layer crystalline (111) whereas the NiC layers are quasi-amorphous. In consequence, the a- NiC/Ti interfaces are sharper than the Ni/Ti ones. Reactive hydrogenation of titanium layers during the deposition process allows us to decrease the neutron refractive index. In this case, the contrast between the high and low refractive index increase and the Ni/Ti-H multilayers have a better reflectivity than those obtained with pure Ni/Ti materials. Moreover, strong affinity of the titanium for hydrogen reduce the Getter effect corresponding to a stabilization of the titanium layers. Accordingly, better contrast and better interfaces are obtained for NiC/TiH multilayers. Some results of super-mirrors with less than 50 layers using these types of materials are given. In these cases, we obtained more than two times the critical angle of pure nickel with a value close to one for the reflectance coefficient.
Thermal stability of [Ni-Ti] multilayers
Malik Maaza, Claude Sella, Mustapha Kaabouchi, et al.
Diffusion in Ni-Ti multilayers with a period of 120 angstroms is studied in the temperature range of 293 - 743 K by using the grazing angle unpolarized neutron reflectometry. It was shown that Ni diffuses into Ti in this temperature range. The effective diffusion coefficient Deff of Ni into Ti and its corresponding activation energy Qa are determined by measuring the decay of the reflectivity of first Bragg peak arising from the nuclear scattering length density modulation, as a function of annealing temperature at constant time. Two diffusion regimes separated by a pseudo-transition temperature Tc approximately equals 543 K are observed in this Ni-Ti multilayer. The corresponding activation energy values are 0.21 eV and 0.43 eV respectively. The unpolarized neutron reflectivity measurements are completed by crystalline structure, chemical profiling, and magnetic studies.
Development and industrialization of supermirror multilayers used for neutron guides
Francois J. Samuel, Bernard Farnoux, Benedicte Ballot, et al.
Great improvements have been made in realizing super-mirrors multilayers, but only on laboratory scale samples. In particular, supermirrors with a cut off twice that of natural nickel and a reflectivity higher than 97% on (10 X 4) cm2 substrates have been obtained. To use such supermirrors in the construction of neutron guides, it was necessary to reach the same results on much larger pieces. We describe the design and set up of special equipment for super polishing the substrates, and sputtering the multilayer-control equipment which has been realized for factory acceptance of each piece.
Low d-spacing titanium-based multilayers for neutrons
Pierre Boher, Philippe Houdy, Andreas Magerl, et al.
The number of bilayers required in a neutron multilayer mirror depends directly on the different scattering cross sections of the materials selected for this purpose. So, conventional systems generally alternate two metallic systems: one with a high scattering cross section like Ni and one with a negative cross section like Ti. In this study, we show that more complicated systems such as TiN/Ti have improved potentials compared to conventional systems, due to the high scattering cross section of nitrogen. We present an experimental study of this new system using a pseudo-reactive rf-sputtering system and different in-situ and ex-situ characterization methods. Well-defined multi-layer structures are obtained with periodicities in the range 20 - 70 angstroms. Titanium and titanium nitride layers appear crystallized even for very low thickness. This induces a quite high interface roughness as observed by grazing x-ray reflection and transmission electron microscopy. Long range roughness appears limited and neutron reflectivity measured with cold neutrons ((lambda) equals 3.96 angstroms) is promising even for short periods around 40 angstroms.
Application of the velocity-dependent spin-flipper in neutron optical devices (Invited Paper)
Mikhail M. Agamalian, N. Pleshanov, Valery Pusenkov
In this paper is described several types of velocity-dependent spin-flippers and their application in the scheme of magnetic monochromator of polarized neutrons designed at the Petersburg Nuclear Physics Institute. Efficiency of the magnetic monochromator is comparable with the best types of crystal monochromators and mechanical selectors but only the magnetic monochromator makes it possible to variate the wavelength, the width and the shape of thermal neutrons spectrum in the wide range without changing the geometry and the cinematic of the device. Up to now, development of this perspective method of monochromatization is limited by a 'background problem' connected with the presence of non- monochromatic neutrons produced by the polarizing elements of the device. It is shown that this problem is solvable and possible solutions are discussed.
Supermirror transmission polarizers for neutrons
Charles F. Majkrzak, Valerie Nunez, John R. D. Copley, et al.
We describe several geometrical configurations of supermirror arrays for polarizing cold and sub-thermal neutrons in transmission with high efficiency, which is particularly important in applications where several polarizers occur in series. The measured polarizing efficiency and reflectivity of Fe-Si supermirror coatings which can be used in these devices are also reported.
Polarized Beams
icon_mobile_dropdown
Polarizing supermirror devices: some new developments
Ferenc Mezei
Transmission geometry neutron optical polarizer devices offer very substantial advantages compared to conventional bender systems by low inherent indensity losses and by conserving the angular distribution of the beam. In order to achieve high polarizations they require very high reflectivity polarizing supermirrors. A technique of producing this kind of mirrors with a reflectivity >= 97% has now been established at BENSC. Both the calculations based on measured supermirror characteristics and the first partial experimental results confirm the expected high performance of so-called 'polarizing cavity' type transmission devices. Another result of polarizing neutron mirror studies at BENSC is the development of single layer totally reflecting coating with high magnetic remenance which is adequate for use in neutron polarizers placed in zero or even oppositely oriented magnetic fields.
Multilayer Characterization
icon_mobile_dropdown
Thin films for neutron optics
O. Elsenhans, Peter Boeni, H. P. Friedli, et al.
Thin film multilayers play a crucial role in the efficient transport of neutrons from the source to the experiments at the Swiss Neutron Spallation source SINQ. In order to develop and optimize the neutron optical components, a magnetron sputtering facility has been installed at PSI aimed at the deposition of thin films covering large substrate area. Initial uniformity tests are very encouraging showing thickness variation of only 1% for 5 nm layers over an area of 500 X 400 mm2. A detailed study of the structure and stability of Ni/Ti multilayers in relation to the deposition conditions is underway and results from analysis using TEM, neutron and x-ray diffraction and reflection are presented. The results point toward the use of alloyed materials and reactive sputtering to sharpen and stabilize the interface between Ni and Ti.
Characterization of neutron mirrors and supermirrors using x-ray and neutron measurements
Z. Jiang, Bernard Vidal, Michel Brunel, et al.
Neutron mirrors and super-mirrors (Ni/Ti, NiC/Ti, Ni/TiH and NiC/TiH) are prepared on borkron (float) glasses or silicon wafers. The period d of the multilayers can be obtained by using small angle x-ray diffraction like those obtained with the white neutron beam measurements made at SACLAY. Large-angle x-ray diffractions can give the structures of the materials, namely, amorphous or crystalline states, and the textures. X-ray rocking curves can further determine the degree of texture perfection. By mixing carbon into nickel layers, the crystalline size of Ni was reduced. As a consequence, smoother interfaces are expected and indeed have been confirmed by x-ray reflectivity in NiC/Ti multilayers. This effect is observed directly by cross-sectional sampled transmission electron microscopy. Nickel still had a cubic structure after mixing the carbon. The addition of a small amount of carbon into the nickel layers can increase in neutron scattering length density by several percentages, but hexagonal Ni3C can only yield a 0.5% improvement as compared with pure nickel. Putting hydrogen into the titanium layers not only made the neutron scattering length density more negative but it also prevented interdiffusion between the nickel and titanium layers. In order to compare their thermal stability, three multilayers, Ni/Ti (100 layers), NiC/Ti(100 layers) and NiC/TiH (20 layers), were chosen to be annealed at different temperatures. Then x-ray diffractions were used to study the structures of their layers. All these characterization are essential at the beginning of the fabrication of neutron mirrors and supermirrors.
Supermirror neutron guide coatings
Charles F. Majkrzak, John F. Ankner
The reflectivities of some commercially manufactured supermirror guide coatings are reported and the effects of interfacial roughness and interdiffusion on the specular reflectivity examined. Uniform reflectivity profiles with average reflectivities of .95 or better out to three times the critical angle of ordinary Ni have been measured. Such high quality coatings can dramatically increase conventional cold neutron guide tube conductance and make possible significantly improved thermal guides.
Supermirror neutron guide
Benedicte Ballot, Francois J. Samuel, Bernard Farnoux
We present the results of investigations by grazing incidence neutron reflectometry of supermirrors NiC/Ti. Their effective critical angle is 1.9 times the critical angle of natural nickel. With these supermirrors, a curve neutron guide has been installed in the neutron guide hall of the ORPHEE reactor. This guide, called G5bis, has a radius of 155 m. The total flux measured at the guide exit is 1.22 109 n.cm-2.s-1. the layout and performances of the new guide are compared to the guide G5 and to a classical multichannel bender.
High-performance neutron supermirrors deposited using an automatic accurate-thickness monitoring technique
Claude Sella, Malik Maaza, Mustapha Kaabouchi, et al.
High reflectivity neutron mirrors require perfectly smooth, sharp interfaces, uniform layer thicknesses and densities and high stack regularity. For this, the multilayers were deposited on water cooled glass substrates using a D-C low energy (300 - 700 V) triode sputtering unit equipped with an accurate thickness monitoring system. This last one is based on the dependence of the deposition rate on the target current. During deposition, the target current is sampled and converted to a digitalized voltage. This voltage value is then fed to a computer where a real-time numerical integration is made. The target current is integrated and the film thickness is given by the integration time. All sputtering parameters are regulated. A feed- back system between anode current and filament heating supply keeps the plasma current constant. The computer also automatically controls the setting and the timing of the runs. Thicknesses can be controlled to an accuracy of better than 1A. Reproducibility is better than 1%. Therefore, a high stack regularity can be achieved with sharp interfaces as will be shown by the characteristics of a 10[Ni-Ti] neutron monochromator. The experimental and theoretical reflection profiles are in perfect agreement indicating a high stack regularity. This technique is also efficient at producing high reflectivity aperiodic media: supermirrors. A 15[Ni-Ti] supermirror in Hayter-Mook configuration gives a neutron reflectivity of the order of 95% with an effective critical angel of 1.9(theta) cNi. The characteristics of the previous monochromator and supermirror have been measured also using secondary ion mass spectrometry, grazing angle x-rays reflectometry, and resistivity measurements.
rf-sputtered Fe/Ge multilayers for neutron-polarizing monochromators
Pierre Boher, Philippe Houdy, M. Monkenbusch, et al.
State of the art diode rf-sputtering is used to fabricated high quality polarizing monochromators for neutrons. Optimization of the deposition parameters is achieved using in- situ kinetic ellipsometry and a great number of ex-situ characterization techniques such as grazing x-ray reflection, x-ray diffusion, alternating field gradient magnetometry. Mossbauer spectrometry, and electron microscopy. A precise picture of the structural characteristics of the system is deduced and related to the neutron performance as measured by polarized neutron reflectometry. We show that the structural behavior is controlled by crystallization of the iron layers and by the occurrence of amorphous interdiffused layers at each interface. As a consequence, the polarizing efficiency of these mirrors depends directly on the amount of iron involved in the interdiffusion. Using optimized deposition conditions, the flipping ratio is found to be around 40 for Fe/Ge mirrors with a medium period value of 120 angstroms. Positive spin-state reflectivity at the first Bragg peak is close to 100% when 150 bilayers are included and a controlled graded layer thickness allows the angular acceptance to be enhanced up to 39%.
Multilayer Monochromators
icon_mobile_dropdown
Multilayer monochromators and supermirrors for neutron protein crystallography using a quasi-Laue technique
Benno P. Schoenborn
The major problem in neutron protein crystallography is the low flux of present neutron sources. The collection of a data set using a conventional rotation technique and a 2D detector takes many weeks. One way to increase the flux at the sample is to increase the wavelength bandwidth. The conventional technique using a standard monochromator like Cu or Be has a typical bandwidth of 1%. A multilayer monochromator can however be tailored to give bandwidth up to 25% or even larger and have an angular acceptance angle of approximately .3%. This can be achieved by a multiple spacing multilayer. In this case the diffraction geometry is such that the reflection in diffraction condition is 'scanned' by the (Delta) (lambda) and not by rotating the reciprocal lattice point through the Ewald sphere. Wavelength bandwidth of 10% satisfy this condition. It is important to tailor the bandwidth to the size needed by the extend of the reciprocal lattice 'point' to minimize background. The intensity of the reflection is proportional to the (Delta) (lambda) r that just covers the width of the reciprocal 'point' while the background is proportional to the full wavelength spread (Delta) (lambda) that hits the crystal. The conventional Laue technique is not suitable since it increases the background by the ratio of (Delta) (lambda) /(Delta) (lambda) r, a ratio that can easily reach multiples of 10.
Determination of reflectivity curves of multilayer neutron monochromators
Alexander Mihai Popovici, Brent J. Heuser, William B. Yelon, et al.
The technique of measuring neutron multilayer monochromator reflectivities by double diffraction rocking curves is discussed. Two problems encountered are deposition induced curvature of multilayer support and lateral variation of layer spacing. Transmitted rocking curves were measured with a narrow detector in an effort to understand these specific problems. General formulae for interpretation of such rocking curves are derived and the methodology for determining relevant parameters is discussed. Measured reflectivities of 10 nm spacing Ni-Ti multilayer devices are presented. Consideration of support curvature and layer spacing variation is essential in understanding observed data.
SANS wavelength selection using a multilayer neutron monochromator
Brent J. Heuser, Alexander Mihai Popovici, William B. Yelon, et al.
A small angle neutron scattering instrument is currently being designed at the University of Missouri Research Reactor. An anti-parallel arrangement of two Ni-Ti multilayers will serve as a neutron monochromator for this instrument. The first multilayer will be flat and in soller, or transmission, geometry. The second will be curved and in the conventional reflection geometry. The curvature of the second multilayer is designed to eliminate resolution asymmetry and increase the incident neutron intensity. The intensities are still too low with this arrangement, but can be increased two or threefold by depositing a second or third bilayer group with a spacing slightly offset from the first group.
Reflectometry: Applications
icon_mobile_dropdown
Neutron reflection studies on magnetic superlattice (Invited Paper)
Yasuo Endoh
Polarized neutron experiments of both reflection and small angle scattering by using mainly pulsed neutrons were performed from various magnetic superlattice films. The long range order in a magnetic unit cell is determined by the conventional neutron diffraction method. Besides the order of the atomic magnetic moment, the semi-macroscopic, often called mesoscopic modulation of magnetization averaged over the magnetic layer is determined by the surface reflection as well as the small angle diffraction. The effect of giant magneto- resistance of a current topic in the solid state physics is strongly related to the semimacroscopic magnetic structure or interface magnetization. The present paper shows that the polarized neutron reflection as well as the small angle diffraction by using long wavelength polarized neutrons are indispensable tools for the magnetic structure investigation related to this subject.
Neutron reflectivity studies of polymers adsorbed at solid-air and solid-liquid interfaces (Invited Paper)
Sushil K. Satija
Over the last ten years, neutron reflectivity has emerged as a powerful technique for the investigation of surface and interfacial phenomena in many different fields. In this paper, a short review of some of the work on neutron reflectivity form polymer films performed at NIST reactor is presented. Specific examples of ordering in diblock copolymer films as well adsorbed polymer brushes are presented.
Neutron reflectometry study of thermally induced boron diffusion in amorphous elemental boron
Gregory S. Smith, William A. Hamilton, Michael R. Fitzsimmons, et al.
We have begun a series of neutron reflectometry studies to investigate atomic diffusion behavior in both elemental boron and refractory transition-metal borides. In this paper, we report on the results for boron-atom self-diffusion in amorphous elemental boron. The samples used for the measurements were thin-film bilayer structures consisting of alternating layers of isotopically enriched 10B and 11B, deposited by electron-beam evaporation. The reflectometry studies were performed with a beam of pulsed neutrons having a broad thermal spectrum incident on the samples at an angle of approximately 1.00 degree(s). Specularly reflected neutrons were detected as a function of their time-of-flight with a position-sensitive detector. This data was reduced to obtain a plot of the reflectivity vs. the perpendicular wavevector. Because of the different nuclear potentials for the two boron isotopes, an interference pattern was observed, analogous to those obtained by X-ray measurements on samples with a modulated index of refraction. Reflectivity profiles were measured and analyzed as a function of annealing time for temperatures of 360 degree(s)C and 400 degree(s)C. Variations in the interference patterns were then used to determine the diffusion coefficient, D, at 360 degree(s)C, and hence the intrinsic diffusion parameters. A typical equilibrium result was determined to be D approximately 10-1 angstroms2s, measured at an annealing temperature of 360 degree(s)C. The measured diffusion constants are inconsistent with the high melting temperature of elemental boron, but are consistent with measured diffusion constants in other amorphous thin films.
Measurement of magnetic-field depth profile in superconducting niobium film by polarized neutron reflectometry
Daniel A. Korneev, L. P. Chernenko, A. V. Petrenko, et al.
The profile of the stationary magnetic field penetrating into the superconducting niobium films was measured by specular reflection of thermal polarized neutrons. At 4.9 K and at 500 Oe the field penetrates practically without attenuation into the depth of (xi) equals 28 nm near the vacuum boundary, which is connected with the nearsurface depression of the superconducting order parameter. Further, in the depth of the film, the attenuation corresponds to a London law with the decay constant (Lambda) equals 45 nm. The measurements are done on the polarized neutron spectrometer SPN at the IBR-2 pulsed reactor at Dubna.
Reflectometry: Analysis
icon_mobile_dropdown
Subsurface profile refinement for neutron specular reflectivity (Invited Paper)
John F. Ankner, Charles F. Majkrzak
The importance of modeling in the analysis of neutron and x-ray reflectivity data cannot be overstated. For specular reflectivity, the theory is straightforward and one merely needs a flexible pattern for constructing density profiles. We will describe the parameters used in and the limitations of such models.
Diffuse neutron scattering signatures of rough films
Patterns of diffuse neutron scattering from thin films are calculated from a perturbation expansion based on the distorted-wave Born approximation. Diffuse fringes can be categorized into three main types: those that occur at constant values of the incident or scattered neutron wavevectors, and those for which the neutron wavevector transfer perpendicular to the film is constant. The variation of intensity along these fringes can be used to deduce the spectrum of surface roughness for the film and the degree of correlation between the film's rough surfaces.
Determination of nonmagnetic density profiles using polarized neutron reflectivity
Charles F. Majkrzak, N. F. Berk, John F. Ankner, et al.
It is in principle possible to recover phase information regarding an unknown, non-magnetic film structure in reflectivity measurements with polarized neutrons if the film is deposited on a substrate with a buried ferromagnetic layer of known thickness. One particular method is described here for inverting plus and minus neutron reflectivity data in the kinematic limit to obtain the chemical density profile of an 'unknown' layer. Application of this method in the dynamical regime is not as straightforward, and will be discussed. Nonetheless, experimental results demonstrate the value of simultaneously fitting plus and minus reflectivity data in the dynamical case in limiting the number of possible ambiguous results.
Inverting neutron reflection data
Devinderjit Singh Sivia, Roger Pynn
We describe a method that makes use of a magnetized substrate and polarized neutrons to determine a unique density profile from neutron reflectometry measurements. Numerical simulations indicate that the method is capable of detecting subtle features such as slowly varying density profiles.
Reflectometry and Microscopy: Instruments
icon_mobile_dropdown
Reflectivity and profile studies in ultracold neutron mirror reflection and grating diffraction
Albert Steyerl, S. S. Malik, A. C. Nunes, et al.
We report high-resolution measurements of ultracold neutron reflection on mirrors as well as of diffraction by a ruled reflection grating. This work crucially depends on the very high resolution provided by the 'gravity diffractometer' for ultracold neutrons (UCN) installed at the UCN Turbine Source of the Institut Laue-Langevin. The samples employed consist of glass, nickel-coated glass, a Fomblin liquid mirror and a ruled optical diffraction grating. The main results are as follows: (1) The reflectivity data for the Fomblin oil is in excellent agreement with the Fresnel formula of elementary analysis while solid mirrors show significant deviations. (2) A detailed line profile analysis for zero-order diffraction on the grating shows no measurable deviation (at the level of 2 X 10-11 eV in line broadening) from the reflection profile for a solid mirror.
Microscopy with ultracold neutrons
Alexander I. Frank
Neutron microscopy is in the initial stage of its technological development. We pin our greatest hopes on the use of ultracold neutrons (UCN) as the preferred method of investigation. The experiment here shows that it is possible to build the neutron microscope with UCN in spite of the largely disturbing action of gravity. However, this possibility is presently limited by the low intensity of available UCN sources. The most promising sources are phase contrast and polarization neutron microscopes.
Time-of-flight four-beam neutron reflectometer REFLEX at the high-flux pulsed reactor IBR-2: some polarized neutron reflectometry applications
V. L. Aksenov, Daniel A. Korneev, L. P. Chernenko
This paper discusses the new neutron reflectometer being built on the high flux pulsed reactor IBR-2 in Dubna. A new method is suggested for measuring and interpretation of data in the study of inhomogeneous (noncollinear) magnetization depth profile in thin films. It is important to take into account the surface roughness in the interpretation of the data from the measurements of the magnetic field penetration depth in superconductors.
Neutron reflectometry and high-resolution imaging
U. Jeng, S. J. Quagliato, L. R. Iyengar, et al.
This paper describes the thermal neutron reflectometer recently installed at the Rhode Island Nuclear Science Center (RINSC) and presents first results. The reflectometer utilizes a narrow 'pencil beam' with an adjustable angle of incidence on the horizontal sample surface. It permits reflection studies with the neutron beam slanting upward or downward in the range up to 0.03 radians allowing measurements to be made from above or from below (e.g., through the sample substrate). We report the results of measurements of specular reflectivity for liquid D2O, for Fomblin oil, and for a polarizing super-mirror. These results are in good agreement with expectation. We also discuss a proposed high resolution imaging device for ultracold neutrons ((Delta) Qz equals 10-9 angstroms-1). This resolution would constitute an improvement of two orders of magnitude beyond the currently available techniques. The imaging system utilizes a pair of hyperbolic mirrors and a flat horizontal mirror surface represented by a lake of Fomblin liquid.
Neutron Focusing
icon_mobile_dropdown
First experience with the focusing neutron guide on IN10C
Andreas Magerl, B. Frick, Klaus-Dieter Liss
Neutron backscattering has been invented just about 25 years ago"2. It is based on the fact, that the precision of the wavelength iX/X of a neutron beam after reflection from a crystal improves with increasing Bragg angle 8. In fact, zLX/X becomes infinitely small for 0 =900 in the usual first order approach in kinematical theory. Closer inspection involving dynamical scattering theory reveals that the wavelength spread is given b
Neutron focusing using capillary optics (Invited Paper)
Muradin A. Kumakhov, V. A. Sharov, V. V. Kvardakov
Multiple reflection neutron capillary optics is described, along with a review of technology. The description of a prototype neutron lens is presented together with experimental measurements and results.
Promise of silicon wafer microguides for future neutron optical elements
David F. R. Mildner, Huaiyu Heather Chen-Mayer, Andreas Magerl, et al.
The usually large cross section of the incident neutron beam is divided in the microguide into a large number of thin slices. This allows the neutron beam to be deviated by a large angle within a short distance and enables the design of an efficient neutron lens by giving the stack an appropriate shape. We present a novel approach for high quality microguides by using thin and thus flexible single crystal silicon wafers as the neutron transmitting medium, coated with optimized neutron reflecting thin-film materials. A crucial issue concerns the reflection coefficient R of the silicon thin-film interface. We have performed neutron transmission measurements through commercially available 200 micrometers thin wafers coated in both sides with nickel. Various rocking curves have been taken on assemblies of straight wafers with neutron pathways from 50 to 200 mm in silicon, and on curved wafers. A reflectivity value of 0.988 +/- 0.005 has been found for a neutron wavelength of 7 angstroms.
Development of a focusing mirror for SANS
John G. Barker, Charles J. Glinka
A 2.4 meter long, doubly curved, grazing incidence mirror is being developed for a 30 meter high resolution small angle neutron scattering (SANS) instrument now in operation at NIST's Cold Neutron Research Facility. A focussing mirror can in principle yield a higher flux at the sample for a given angular resolution than the pinhole collimation normally used in SANS instruments, provided that a sufficiently sharp focus can be achieved. The mirror is being constructed from 8, 30 cm long, concave cylindrical quartz segments that have surfaces with a mean roughness, (alpha) s, ranging from 0.3 to 0.9 nm. The mirror segments will be aligned along an arc and bent slightly to approximate an overall toroidal shape. The results of design calculations for the mirror system; of neutron reflectivity measurements of the specular and nonspecular scattering from the individual mirror segments and from test pieces with nickel coatings; and tests of the mirror bender are described. From these results, the overall gain in flux that can be realistically expected from the completed mirror system is estimated.
Characterizing a neutron lens: study of capillary optics
Huaiyu Heather Chen-Mayer, Robert Gregory Downing, David F. R. Mildner, et al.
A neutron lens constructed with glass capillary fibers has been used to focus neutron beams of various geometries and wavelengths. We give as an example measurements performed at an end position of a 58Ni-coated cold neutron guide, where the exiting neutron beam with a cross section of 30 mm in diameter from the guide is incident on the lens and is focused to a 1 mm diameter spot, with a gain of 3.6 in neutron flux density. We have evaluated various features of the focusing performance of the lens, as well as some neutron properties of individual capillary fibers. The average reflectivity of the inner wall of the fibers has been determined to be greater than 0.99. The results of this study will be used for the design and construction of future lenses for neutron absorption experiments such as depth profiling and prompt gamma activation analysis.
Crystal Diffraction Optics
icon_mobile_dropdown
Toward a perfect crystal resonator
Martin Schuster, Colin J. Carlile, Erwin Jericha, et al.
In the last few years we have shown that neutron pulses can be caught in between perfect crystal plates where they have been reflected back and forth up to 78 times. The quality factor of such device strongly depends on the reflectivity of the crystals and the neutron guide placed in between the crystal plates, as well as on the adjustment and stability of the set-up. The storage of more than one neutron pulse and a significant improvement of the present storage capability seems to be possible. Various novel beam tailoring methods and advanced phase space transformations can be envisaged. The question whether the back and forth motion is a coherent or incoherent process will be discussed as well as possible electromagnetic interactions during this motion.
Unconventional double bent-crystal diffractometer equipped by position-sensitive detector
Pavel Mikula, Petr Lukas, Jiri Kulda, et al.
Using Bragg diffraction optics, an unconventional DBC diffractometer was tested for medium resolution small-angle neutron scattering experiments. The diffraction geometry of the analyzer enables to transform the angular beam distribution into the positional distribution and, consequently, to analyze it by means of a one-dimensional position sensitive detector. First experimental results obtained with a sample of PE+graphite proves a compatibility and a higher speed of data collection compared to a standard DBC diffractometer.
Neutron microfocusing by double reflection on curved perfect crystals
Alexander Mihai Popovici, William B. Yelon
The imaging of large area neutron sources into millimeter-size spots by focusing with two curved perfect crystals is examined. In the parallel (+,-) setting large demagnifications can be achieved only with crystals in strongly asymmetric reflection. The most promising configurations appear to be those with crystals in antiparallel (+,+) setting. The beam intensities for the parallel and antiparallel settings of bent crystals are comparable, the reflection efficiency being enhanced by the reflectivity curve broadening. The instrument Q-resolution can be kept reasonably good in a limited range by phase space focusing. Results of neutron optics computations are presented for a diffractometer for stress scanning measurements and for a small-angle scattering instrument with long neutron paths.
Use of focusing by bent perfect Si crystals for short-wavelength neutron monochromatization
Volker Wagner, Pavel Mikula
Reflectivity and resolution properties of cylindrically bent silicon crystals were investigated for their possible employment as short wavelength monochromators. We report flux density measurements of monochromatic neutrons at the sample position of a conventional diffractometer in the wavelength range from 0.05 nm to 0.09 nm for Si(311) and Si(422) reflections. From the obtained data, the optimum crystal thickness and bending radius for a chosen neutron wavelength and the gain in intensity in comparison with a flat mosaic monochromator can be estimated. Further, the use of momentum space focusing in diffraction experiments is discussed.
Instrumentation for strain measurements using cylindrically bent perfect crystals
Petr Lukas, Miroslav Vrana, Pavel Mikula, et al.
Experimental tests of elastically bent Si crystals as monochromator and analyzer in a triple- axis setup for investigation of stress fields in polycrystalline materials are presented. It is also demonstrated that if certain focusing conditions for a bent monochromator are met the beam diffracted by a polycrystalline sample becomes quasi-parallel which enables high resolution measurements directly with a PSD without the use of a collimator or a crystal-analyzer. In the three axis setup maximum sensitivity in determination of (Delta) d/d <EQ 10-4 can be achieved permitting profile-broadening analysis for reasonable sample volumes and counting times.
Section
icon_mobile_dropdown
Performance of beam bender for very cold neutrons
Yuji Kawabata, Masahiko Utsuro, Tohru Ebisawa
A VCN bender has been installed behind the VCN guide tube in the UCN-VCN facility of KUR. The design and the performance of the VCN bender is described in this paper. The neutron spectra at the end of the VCN bender has been measured by the reflection method using a multilayer monochromator. Neutron radiography films were used to know the neutron flux distribution. The VCN gain factor of the CNS is also derived from the spectrum measurements at the end of the VCN guide tube and the VCN bender.
Focusing arrangement of a fall-focusing gravity analyzer for ultracold neutrons
Yuji Kawabata, Masahiko Utsuro
A prototype gravity analyzer using UCN has been constructed in KUR. The principle of the scattered energy analysis is 'fall-focusing'. The scattering angle is divided into five sections to analyze the momentum transfer. The second and fourth regions of five divisions are already installed in this analyzer. The gravity analyzer using UCN has a high resolution for both energy and momentum. The present device has a high geometrical efficiency because reflection mirrors with wide solid angles are provided to collect scattered neutrons.
Possibility of magnetic pumping of very cold neutrons in a guide-tube torus
Masahiko Utsuro, Yuji Kawabata
Very cold neutrons (VCN) with the velocity below about 40 m/s can be confined in a guide tube torus with the tube diameter of about 5 cm and curved with a radius of about 4 meters. Thus, arranging a number of magnetic devices along the torus which force adiabatic spin flips of VCN in the strong magnetic field, a magnetic pumping of VCN into a defined energy band can be attained and a high density of ultracold neutrons will be produced with feeding VCN continuously from a connected guide tube. An analytical work on the proposed system with the realistic design parameters under actual VCN feeding intensity from the KUR VCN facility will be reported. The preparation of an experimental device is also under progress according to the present analysis in order to test the working principle of the proposed magnetic pumping of VCN to ultracold neutrons.
Neutron diffraction optics of films with noncollinear magnetic depth structures
Daniel A. Korneev, L. P. Chernenko
A model of a thin film with depth inhomogeneous or noncollinear magnetization is used to describe its neutron-optical, diffraction, and polarization properties. A quantum mechanical method of calculation is developed based on a numerical solution of the Pauli equation for a neutron in inhomogeneous matter with boundary conditions. This solution permits the uniform calculation of intensities and the polarization vector of the scattered beam over a wide range of conditions from specular reflection to neutron diffraction. The method is applied to certain model structures. Examples of its application to model structures (ferromagnetic spirals, long- period soliton) are given and the calculation can be programmed for a personal computer, taking a few seconds for each value of the incident neutron wave vector.
New aspect in employing magnetic anisotropic FeCo thin films as neutron polarizers
Daniel A. Korneev
The reverse of the beam polarization vector is the necessary procedure in carrying out the experiments by polarized neutrons. At the present time, a number of methods and set-ups (spin-flippers) are widely used in experiments by the thermal polarized neutrons. A new way to get the neutron beam polarization of a necessary sign during the process of neutron specular reflection from ferromagnetic anisotropic mirrors is proposed. The results of its check-up on a neutron polarized beam are given. The measured spin reverse probability by this method is near unity, and it does not practically depend on a neutron wavelength. The application of this method allows one to exclude the spin-flipper as an element of polarized neutrons set-ups.
Multilayer Characterization
icon_mobile_dropdown
From 1 to m: the development of supermirrors (Invited Paper)
Ian S. Anderson
Since the discovery of the total reflection of thermal neutrons more than 40 years ago by Fermi and co-workers, mirror reflection has been successfully applied to neutron beam transport and optics. In order to overcome the limitations of small critical angles of reflection, Mezei and others proposed the use of multilayers, termed supermirrors, designed to increase the angular range of neutron reflection. Since then a certain amount of effort has gone into improving the angular range, reflectivity, and polarization of supermirror devices. This effort has been applied not only to the theoretical design of the multilayer sequence but also to the practical problems of depositing thin films such as uniformity, roughness, and inter- diffusion.
Section
icon_mobile_dropdown
Fe-Al neutron polarizing supermirror on Si crystal substrate with antireflecting Cd layer
V. G. Syromyatnikov, Anatoly F. Schebetov, Z. N. Soroko
Experimental data and the results of calculations are presented for an Fe-Al neutron polarizing supermirror on a Si crystal substrate with an antireflecting Cd layer. The supermirror polarizing efficiency is P >= 0.8 in the range of 'normal' wavelengths. Applications of this supermirror are also considered.