Production of copper and Heusler alloy Cu_2MnAl mosaic single crystals for neutron monochromators

摘要

The growth of high-quality, large single crystals of copper allows the production of very efficient double focusing copper monochromators at ILL. The main difficulty of adapting the crystal mosaic to the instrument requirements has been overcome through the development of specific techniques such as the "onion peel" method and plastic deformations at high temperature. Several instruments have been equipped with new copper monochromators allowing a significant gain in the neutron flux onto the sample. ILL also produces Heusler single crystals with a controlled mosaic for polarized neutrons. Recently, an order of magnitude increase in polarized neutron flux has been reached on the triple axis spectrometer IN20 using a new Heusler monochromator. In addition, the Neutron Optics Laboratory carries out developments in the field of new materials for neutron monochromators. Mixed gradient crystals have been successfully grown with a variation in the d spacing Δd/d ≈ 10~(-2). Studies on new polarizing crystal alloys are also in progress and NiMnSb Heusler alloy having partially enriched Ni with ~(60)Ni may be interesting for polarized neutron applications.