Partner und Internationale Organisationen
(Englisch)
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Rutherford Appleton Laboratory, Chliton, Didcot (UK), Commissariat à l'Energie Atomique, CEA, Grenoble (F),
Technische Universiteit Delft, Delft (NL), Hahn-Meitner-Institut Berlin GmbH, Berlin (D), Institut Laue-Langevin, Grenoble (F),
Instituto Natzionale per la Fisica della Materia, INMF, Genova (I)
Paul Scherrer Institut, Villigen, (CH)
Riso National Laboratory, Rosklide, (DK)
Commissariat à l'Energie Atomique, CEA, Saclay, (F)
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Abstract
(Englisch)
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Multilayers of Ni/Ti and FeCoV/Ti have been studied for their use in various neutron instruments such as guides, focusing units, and polarisers. Structural, mechanical and magnetic properties of the multilayers and supermirrors have been investigated in detail and the number of layers has been increased to more than 2500.
Report:
The aim of the programme was to produce supermirrors with high critical angles of reflection in order to obtain flux gains of more than about 5 for cold neutrons. In order to achieve this goal the interface properties of the multilayers and the stress between the artificial superstructure and the substrates has to be well understood and controlled. Finally, the coatings must be produced on a large scale and incorporated into useful neutron optical devices.
In a first step, we have assembled a new sputtering plant for the production of test coatings. Reflectivity measurements and stress measurements on these samples were carried out using a profilometer and X-ray diffraction. The magnetic properties have been investigated by means of a vibrating sample magnetometer. Finally, focusing and polarising devices were tested using beam lines at the Swiss spallation neutron source SINQ.
The results show that the interface roughness, interdiffusion and the stress of the layers can be controlled by the incorporation of nitrogen and oxygen into the Ni and Ti layers. The magnetisation measurements demonstrate that the coercivity decreases with decreasing layer thickness. Still, by using anisotropic sputtering conditions it is possible to produce multilayers with a remnant magnetisation. These are the only know mirrors that can be produced to polarise neutrons in zero magnetic field.
Finally, we have constructed beam devices that polarise and focus neutron beams efficiently on the sample and lead to the anticipated flux increases of a factor of five or more. In 1999 the first user-experiment with polarised neutrons has been successfully performed at SINQ using remnant benders based on FeCoV/TiN layers.
The results of our contribution to the XENNI programme have been presented at most international meetings on neutron scattering in the form of invited talks or lectures. The results have been published in 18 papers. The technology has been transferred to industry. In the future, we plan to improve the roughness of the interfaces further in order to achieve even higher reflectivities.
Repor_2000.doc
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