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NIST Center for Neutron Research

CHRNS MACS

NSF: Multi-Axis Crystal Spectrometer (MACS)

Polarized Beam Capability

The schematic shown above illustrates the application of ³He NSFs on MACS using 2 wide angle analyzers and 1 polarizer. The MACS (Multi-Axis Crystal Spectrometer) instrument is a new high intensity cold neutron spectrometer in operation at the NIST Center for Neutron Research. The cold neutron beam is filtered by a Be cooled filter and doubly focused by a 1428 cm² PG monochromator. The incident neutron beam is polarized by a ³He cell (polarizer) before striking the sample. The scattered beam is analyzed by one (toroid) or two (wide angle) ³He cells (analyzer) prior to reaching the 20 channel detector system. The polarized beam apparatus consists of a cylindrical ³He spin filter cell in a radio frequency-shielded square solenoid to polarize the incident neutron beam and two three-sectioned wide-angle ³He cells located near the sample and on opposite sides of the main beam or one horseshoe-shape wide-angle ³He cell surrounding the sample to spin-analyze the scattered beam. Both the cells and the sample are contained within a uniform magnetic field of less than 4 mT provided by a vertical, neutron compatible solenoid. Neutron spin flipping of the polarized beam is accomplished by inverting the ³He polarization using the AFP NMR technique. When flipping the neutron spin of the polarizer, the polarization loss to the analyzer is ensured to be negligible. During the experiment, FID is used to monitor the ³He polarization in the spin filter cells. The instrument provides a neutron flux up to 5x10⁸/s/cm² on an 8 cm² sample area. Please select the provided links for general {Chen16, Fu11 } and specific {Hong17} applications. All MACS publications using NSFs can be found here.

Specifications for NSF on MACS
	³He polarizer and analyzer ³He polarization flipping capability (polarizer only) ³He polarization: up to 85% Relaxation times: up to 400 hrs Cell change: 2-4 days Elastic and inelastic measurement Ei from 2.5 meV and 17 meV Sample field magnitude: < 40 G, P \({\perp}\) Q Scattering angle coverage: up to 240\(^{\circ}\) Polarized flux: up to 1 x 10⁸ \(\frac{n}{cm^2/s}\) @ 10 meV Flipping ratio: between 20 and 45 ³He transmission: < 62% (for the desired spin state) Two (four is an option) spin-dependent cross section measurements