Focusing Monochromators for Advanced Neutron Applications

In respond to an increasing demand from domestically-produced neutron optical devices, Phase III Physics LLC will begin the design and prototype production of multi-wafer focusing neutron monochromators. Our monochromators in the early stages of this effort will consist of stacked single crystal Si wafers which are elastically bent to control the crystal mosaicity (and therefore measured neutron linewidth). This scheme was first successfully demonstrated in a collaboration between neutron physicists at ORNL and MURR, who referred to these devices as “Bragg Mirrors (BMs)” and are currently utilized at several neutron facilities worldwide, though such devices are only commercially available from international suppliers. Our work plan will consist of (1) purchasing perfect crystal Si wafers in a variety of lattice orientations, (2) design and construction of a device which can accept and compress a stack of rectangularly-cut wafers, inducing a horizontal radius of curvature Rc (e.g. using the four point bend method), (3) measure available mosaic spreads as a function of Rc using X-ray diffraction, and (4) perform detailed neutron simulation studies and catalog our samples with their neutron monochromation and focusing capabilities. During Phase-II our efforts will be devoted to scaling BM production, including testing on a neutron beamline instrument, such as a triple axis spectrometer, where the neutron focusing properties can be utilized and compared with other monochromators, while we invest in equipment and personnel with crystal growing expertise to develop crystal growing capabilities in-house to expand our product offerings to include compressed mosaic crystals traditionally used as monochromators, including Ge, Cu and HOPG. This effort will be led by Dr. Brian Shevitski, who received his Ph.D. in experimental physics from UC Berkeley in 2019. Dr. Shevitski will leverage his expertise in materials science (synthesis, characterization, crystallography, particle optics, etc.) as well as his experience working in the semiconductor industry. Other Phase III Physics personnel who have extensive experience in experimental neutron physics and neutron Monte-Carlo simulations will support the project.