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The energy resolution of this instrument, the first of two time-of-flight spectrometers to be operating in the NCNR, lies in the range from 60 to 1000 micro-eV. With incident neutron energies from 2.2 to 15 meV, the spectrometer allows a broad range of quasielastic scattering experiments on diffusional motions in solids and liquids, and inelastic scattering experiments on magnetic and vibrational excitations.

The spectrometer is located on neutron guide NG-6, which has a 150 by 60 mm (height x width) cross section. The pulsed monoenergetic neutron beam is produced by a combination of monochromator crystals and a Fermi chopper. The double monochromator consists of two PG crystals, one of which can be curved vertically to focus neutrons onto the sample position. The curvature can be varied automatically to adjust for changes in monochomator-sample distances as the incident energy is varied. Two Fermi choppers with different blade curvatures are available. An oscillating radial collimator between the sample and detectors eliminates scattering from cryostat and furnace shields around the sample position.

Terry Udovic, (301) 975-6241;
Craig Brown, (301) 975-5134;

Schematic of Fermi Chopper Time of Flight


Last modified 07-March-2002 by website owner: NCNR (attn: Bill Kamitakahara)