| This thesis presents a novel multi-crystal double focusing neutron monochromator. It has been developed for the cold neutron triple axis spectrometer, MACS (Multi-Axis Crystal Spectrometer), currently being developed by the National Institute of Standards and Technology (NIST), Gaithersburg, MD, and the Johns Hopkins University, Baltimore, MD. The monochromator utilizes a unique vertical focusing element that enables active vertical and horizontal focusing with a very large, 357-crystal (1428 cm2) array while, at the same time, significantly reducing the amount of structural material in the beam path as compared to currently available devices. Active double focus control enables sample flux optimization over a broad range of incident energy. The combination of such a large diffracting surface and minimal in-beam structural material will facilitate a very high signal-to-noise spectroscopic signal, ideal for studies of very small (∼1 mm3) single crystalline samples, as well as parametric studies of larger (∼1 cm3) samples.; The detailed development of the monochromator is discussed in this thesis. An analytical analysis is presented, which predicts that, when mounted at the NIST cold neutron source, the device should produce a monochromatic beam (ΔE = 0.2 meV) with a peak flux &phgr; > 1.5 × 108 n/cm2/s; a factor of three greater than the most intense cold source currently available worldwide. Independent Monte Carlo simulations have confirmed this result. It is also shown that background will be reduced by a factor of 25 as compared to a comparably sized monochromator with a traditional focusing mechanism. The theoretical and numerical development of the elastic vertical focusing element, upon which this instrument is based, is discussed in detail, and experimental results are presented that verify the excellent focusing performance of the device.; The principal research contribution of this thesis is the development of the precision elastic variable-curvature focusing element that serves as the vertical focusing mechanism for the monochromator. This represents an advance in the field of tunable focal surfaces. |
