From x-ray telescopes to neutron scattering: using Wolter mirrors to focus a neutron beam

Boris Khaykovich (MIT) and Mikhail Gubarev (NASA)

We are developing novel neutron focusing mirrors based on axisymmetric conic sections. In 1952 Hans Wolter described advantages of such glancing-angle optics for an x-ray microscope. This approach is widely used in x-ray astronomy and microscopy and we are extending the technique to the neutron focusing. Wolter mirrors can be made essentially free of optical aberrations. In addition, several coaxial confocal mirrors can be nested to increase the collection efficiency.

We will present the experimental demonstration of the nested neutron mirrors. An optical system containing four nested mirrors has been used to focus a polychromatic neutron beam at the MIT Reactor and to demonstrate a mirror-based cold-neutron microscope at HFIR. The mirrors were fabricated at the Marshall Space Flight Center using the electroform nickel replication technique originally developed for the x-ray astronomy applications. Overview of the progress in the replication technology development will be presented, including the development of replicated neutron supermirror coatings, and other scientific applications of the technology.

Extensive ray-tracing simulations of the mirrors have been carried out for different neutron beam configurations. Notably, calculations show that such mirrors can improve the performance of TOF SANS instruments by orders of magnitude, relative to the basic pin-hole design. The examples of the ray tracing simulation results will be presented.

We envision multiple applications of such Wolter optics, especially taking advantage of their ability for nesting and aberration-free performance. The examples include neutron imaging, both in absorption and phase contrast; focusing and transporting neutron beams while preserving time-of-flight information; and scattering applications, such as SANS.

Research supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award # DE-FG02-09ER46556, # DE-FG02-09ER46557 (Wolter optics studies) and by National Science Foundation under Award # DMR-0526754 (construction of Neutron optics test station and diffractometer at MIT).

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