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Neutron Science
Using Neutron Science for Industrial R&D
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Neutron guide as fabricated by SwissNeutronics for the Institute Laue-Langevin in Grenoble. The glass plates are coated with supermirror m = 2.
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Neutron-beam instrumentation offers a unique, cost-effective tool for efficient R&D in the development of new materials and processes, controlling emerging technologies or exploring future research avenues. Neutrons have no electrical charge so they can deeply penetrate a material抯 structure with limited damage, while also producing measurable interactions at the atomic level.
Neutron-beam instrumentation coupled to scientific expertise can facilitate R&D in such areas as
- The investigation of the microstructure in materials,
- Mechanical stress in metals,
- The behaviour of polymers and colloids,
- The performance of permanent magnets,
- The morphology of magnetic and non-magnetic
surfaces and films,
- Trace element analysis and in situ studies of chemical
reactions in industrial products.
All sectors of industry can benefit from such advanced facilities, from the nuclear power industry through chemicals and pharmaceuticals to advanced engineering.
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Large facilities for neutron research exist for example at the Institute Laue-Langevin (ILL) in Grenoble, France, at Paul Scherrer Institute in Switzerland and at the Technical University Munich in Garching, Germany. These facilities belong to the most advanced and modern neutron sources world-wide, offering an extensive range of advanced scientific instrumentation, constantly optimised to address problems in materials science, solid-state physics, chemistry and bio-medical sciences.
Neutron-beam instrumentation uses guides to transport the precious neutrons from the intense neutron source to the diffractometers and spectrometers in large experimental halls.
The rectangular section of each guide is fabricated from 4 associated flat perpendicular mirrors with typical cross sections of the order of 200 x 30 mm (Fig. 1).
The total length of the guides of up to 120 m is made of successive straight modules having individual lengths of 0.5 m or 1 m , following slightly curved ways in order to remove the intense 冏-radiation from the source, and aligned with a very high accuracy of 5E-5 radian.
The mirrors are made of glass, polished with very low roughness and covered with sophisticated multilayer coatings providing a good reflectivity for the reflection of neutrons (Fig. 2).
Those very complex coatings composed of up to 5000 individual metallic layers are designed to enlarge the critical angle of reflection to very large values. When a neutron beam hits the surface it is reflected by an interference mechanism intrinsic to the physics of thin films. The thickness, the materials properties as well as the number of stacked layers play an important role in the performance of the coating and therefore on its reflection coefficient.
SCHOTT customer SwissNeutronics is able to superpose thousands of layers using DC magnetron sputtering. Of course, the roughness of the substrates is also of primary importance. To limit the scattering of neutrons and therefore the losses of the guide, this roughness has to be in the range of a few angstroms. SCHOTT produces these substrates for Swiss Neutronics.
Protection against the intense neutron radiation is necessary outside the guide all along the way. The mirror substrate is also designed to provide efficient neutron shielding thanks to its Boron10 content. Additional shielding surrounds the guide to protect scientists and high sensitivity instrumentation from intense gamma rays induced by neutron flux attenuation.
Around 30 years ago, ILL was looking for a glass with appropriate boron oxide content giving adequate absorption of neutrons in the glass. SCHOTT successfully developed the glass Borkron N which was specifically designed for those applications. The mirror substrates incorporate efficient neutron shielding through their Boron10 content and, with additional external shielding, protect both scientists and sensitive instruments from intense gamma rays induced by neutron flux attenuation.
ILL is one of the major facilities in neutron experimentation and they decided to give the preference to SCHOTT Borkron N in comparison to other alternative glasses.
Borkron N is used in all critical zones where the radiation intensity is very high and where alternative glasses having similar boron oxide content are quickly damaged.
After a few unsuccessful trials with alternative materials, ILL ordered in 2006, 8 tons of Borkron N for its next equipments.
Other laboratories such as SDH in Germany, LLB in France and NIST in the USA made use of the melting campaign to order one or two tons of the material in their own sizes.
One of the major customers for Borkron glass is SwissNeutronics, the worldˇs largest producer of neutron guide systems. The neutron-reflecting supermirror coatings were developed by using radiation resistant substrates of Borkron N from SCHOTT when the Swiss spallation neutron source SINQ was built in 1994 at Paul Scherrer Institute. It became possible to fabricate low-loss neutron guides with a very high performance by combining the efforts of SCHOTT in attaining a small microroughness and waviness of superpolished Borkron N with the superior sputtering technology and highly precise grinding processes of SwissNeutronics. This way it will become possible to produce very advance neutron bending devices as shown in Fig. 3. Hence major neutron scattering centres in the USA (NIST) and Europe (ILL, LLB, PSI) are presently profiting from the intense collaboration between SCHOTT and SwissNeutronics.
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Fig. 1: Neutron guide as fabricated by SwissNeutronics for the Institute Laue-Langevin in Grenoble. The glass plates are coated with supermirror m = 2.
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Fig. 2: Reflectivity of a supermirror coating with an angle of reflection m = 2 (produced on SCHOTT Borkron N) by SwissNeturonics showing an excellent reflectivity.
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Fig. 3: Multi-channel neutron guide for the Spallation Neutron Source SNS in Oak Ridge National Laboratory (USA). The glass plates are coated with supermirror m = 3.6. The casing is made of stainless steel.
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