Imaging and focusing of neutrons by a zone plate

Abstract

The use of refractive lenses for long-wavelength neutrons,although possible1, is severely limited by the fact that the refractive index differs only very slightly from unity (forexample, n - 1 = 2.3 × 10-4for quartz at λ = 20 Å). However, the fact thatonly a relatively thin layer of material is needed to produce an optical path difference of half a wavelength (for example, 2.4 μm of Cu at λ = 20 Å) led us to propose2 previously that neutrons could be focused by diffraction froma phase grating of variable spacing; this is , in fact, a type of zone plate. Zone plates, first described by Soret3, have been used satisfactorily over a large part of the electromagneticspectrum4-6. We now report the..