The High-Flux Backscattering Spectrometer at the NIST Center for Neutron Research

TL;DR

This paper details the design and performance of a high-flux backscattering spectrometer at NIST, achieving high neutron flux and energy resolution through innovative optical devices and a Doppler-driven monochromator system.

Contribution

Introduction of a novel phase-space transformation chopper and a high-speed Doppler monochromator, significantly enhancing flux and dynamic range of backscattering spectrometers.

Findings

Flux gain of 4.2 due to phase-space transformation chopper

Energy transfer capability up to ±50 μeV

Extended dynamic range over previous instruments

Abstract

We describe the design and current performance of the high-flux backscattering spectrometer located at the NIST Center for Neutron Research. The design incorporates several state-of-the-art neutron optical devices to achieve the highest flux on sample possible while maintaining an energy resolution of less than 1mueV. Foremost among these is a novel phase-space transformation chopper that significantly reduces the mismatch between the beam divergences of the primary and secondary parts of the instrument. This resolves a long-standing problem of backscattering spectrometers, and produces a relative gain in neutron flux of 4.2. A high-speed Doppler-driven monochromator system has been built that is capable of achieving energy transfers of up to +-50mueV, thereby extending the dynamic range of this type of spectrometer by more than a factor of two over that of other reactor-based backscattering instruments.