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CHRNS MACS - The Multi Axis Crystal Spectrometer
NIST Center for Neutron Research
Overview Pictures MACS Publications Documentation
The Multi-Axis Crystal Spectrometer takes advantage of the large solid angle view of the cold source to deliver a high intensity neutron beam at sample position. The large doubly focusing PG monochromator can deliver up to 5x108 neutrons/cm2/s in a 2 cm x 4 cm area at sample position, providing one of the highest neutron beam in the world. Between the monochromator and the sample there is a focusing super-mirror guide that enhances the flux on sample by approximately 20%. Upstream of the monochromator there is a variable beam aperture that controls the overall angular distribution of neutrons that is incident on the sample. There are also radial collimators that control the energy resolution. It is a remarkable aspect of MACS that the Q and E resolution can be controlled virtually independently through these remote controlled devices. The detection system for MACS consists of twenty independent monochromatic channels with variable final energy. There is also an energy integrating detector in each channel. These channels operate simultaneously and in doing so provide 0.15 Sr monochromatic detection plus 0.15 Sr diffraction detection. This is more than an order of magnitude gain in detection efficiency for surveys as compared to a conventional TAS. Actual MACS configuration:

Incident energy: 2.3 to 17 mev

Energy resolution: 0.02 to 1.4 meV (FWHM)

Monochromator: Doubly focusing PG002

Analyzer: 20 analyzers vertically focusing PG(002) providing 0.15 Sr of detection. Cooled Be, BeO and HOPG filterss and 90' collimators before the analyzers.

Detector: 40 He detectors (20 spectroscopic and 20 diffraction detectors)

Flux at sample: 5x108 neutrons/cm2-s at 12meV open collimators