Planar Neutron Waveguides
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anar Neutron Waveguides S. V. Kozhevnikov* Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980 Russia *e-mail: [email protected] Received October 22, 2018; revised November 23, 2018; accepted November 28, 2018
Abstract—A planar neutron waveguide is a three-layer film that transforms a conventional neutron beam into a narrow divergent microbeam. We review the research into planar neutron waveguides and their application in studies of magnetic nanostructures. DOI: 10.1134/S1063779619030031
1. INTRODUCTION 2. RESONATOR STRUCTURES 2.1. Interference Filters 2.2. Fabry–Pérot Cavity 2.3. Resonators 2.4. Waveguides 3. NEUTRON CHANNELING 3.1. Calculations 3.2. Experimental Results 3.2.1. Gd2O3 powder absorber 3.2.2. Sliding bar 4. INVESTIGATION OF WEAKLY MAGNETIC FILMS 4.1. Description of the Method 4.2. Experiments 4.2.1. TbCo5 film 4.2.2. TbCo11 film 5. NEUTRON SONDE MICROSCOPY 5.1. Angular Microbeam Divergence 5.2. Intrinsic Spectral Width of the Resonance 5.3. Microbeam Polarization 5.4. Investigation of a Magnetic Wire 5.5. Microbeam Intensity 6. CONCLUSIONS ACKNOWLEDGMENTS REFERENCES
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biological objects, polymers, and magnetic structures. In contrast to neutrons, X-ray radiation does not feature isotopic sensitivity, interacts strongly with matter, and has low penetrating power. Owing to recent progress in experimental techniques, synchrotron X-ray radiation is now used actively in experiments that were traditionally performed with neutrons (e.g., studies into the protein structure or magnetism in thin films). However, some objects (e.g., bulk magnetic materials) still remain beyond the reach of X-ray studies and need to be probed with neutrons. The scale of studied local nonperiodic structures is determined by the size of the neutron beam. The beam width in a typical neutron experiment is 0.1–10 mm. Narrower beams are needed to examine objects on a micrometer scale. Various focusing devices (refractive lenses, diffraction gratings, bent monochromator crystals, etc. [1]) have been designed for this purpose over the years. They are capable of compressing neutron beams down to 50 μm, but restrictions related to the optical properties of materials and techniques used to process them make smaller beam widths infeasible. Planar waveguides (i.e., three-layer films) are simpler and more efficient tools for producing neutron microbeams. They transform a conventional collimated neutron beam into a narrow divergent microbeam compressed to 0.1–10 μm along one axis.
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1. INTRODUCTION The difference in properties between neutrons and X-ray radiation makes them complementary tools for material studies. Neutrons feature isotopic sensitivity, high penetrating power, and an intrinsic magnetic moment and are a powerful tool for the examination of
Neutron sources produce highly divergent lowintensity beams. These beams are hard to focus, since neutrons interact weakly with matter. Syn
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