8 November 2001 Multiwafer focusing neutron monochromators and applications
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Abstract
Multi-wafer silicon monochromators for neutron focusing instruments have been developed at MURR. A first unit, made from commercial thin silicon [100] wafers with manual control of horizontal curvature was designed and fabricated for the MURR stress machine. It was tested on the stress machine at the HFIR reactor at ORNL. A second similar unit but with stepper motor control of curvature was installed on the NIST stress machine. Both confirmed expectations, with significant intensity gains at equal or better resolution in comparison with the monochromators they replaced. A third unit with two back-to-back assemblies of non-standard silicon wafers custom sliced obliquely from big [100] ingots has been fabricated for an upgrade of the ORNL stress machine. The phase space analysis of the neutron optics of multi-wafer assemblies has revealed exciting new possibilities for applications. The correlation between the coordinates of real space and wavevector space allows a new type of focusing, the thickness focusing. The many wafers in a packet can be made to look as a single wafer when seen from a given point of a position sensitive detector (PSD). This allows high resolutions in scattering, corresponding to a bent thin single wafer, at intensities given by the whole packet, that is comparable with pyrolytic graphite crystals. One can thus have the best of two worlds - but only in PSD instruments. A whole array of new applications becomes possible, including dispersive and non-dispersive neutron imaging at the spatial resolution of a single thin wafer. Some of these applications are discussed and demo experiments are presented.
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Mihai Popovici, Alexandru Dan Stoica, Camden R. Hubbard, Stephen Spooner, Henry J. Prask, Thomas H. Gnaeupel-Herold, Peter M. Gehring, Ross W. Erwin, "Multiwafer focusing neutron monochromators and applications", Proc. SPIE 4509, Neutron Optics, (8 November 2001); doi: 10.1117/12.448073; https://doi.org/10.1117/12.448073
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