A space and energy focusing hybrid cold time-of-flight spectrometer based on a moving monochromator crystal

The concept of a time-of-flight spectrometer for cold neutrons is presented which makes use of the principle of phase-space transformation. A first curved monochromator is combined with a second moving crystal to a double monochromator. At the right velocity this crystal monochromatizes the neutron beam and reduces at the same time its horizontal divergence. With pyrolithic graphite as monochromator focusing can be realized for 5 angstrom <= lambda <= 6.5 angstrom. At lambda = 6 angstrom, an energy resolution delta E similar to 60 mu eV is estimated. Compared to time-focusing instruments improved momentum transfer resolution and good energy resolution at all energy transfers is obtained. The instrument does not need an end position on a neutron guide. (c) 2006 Elsevier B.V. All rights reserved