Neutronxyz– polarization analysis at a time-of-flight instrument

Abstract

Abstract. When implementing a dedicated polarization analysis setup at a neutron time-of-flight instrument with a large area detector, one faces enormous challenges. Nevertheless, significant progress has been made towards this goal over the last few years. This paper addresses systematic limitations of the traditional method that is used to make these measurements, and a possible strategy to overcome these limitations. This will be important, for diffraction as well as inelastic experiments, where the scattering occurs mostly out-of-plane.

Polarized neutron scattering on HYSPEC: the HYbrid SPECtrometer at SNS

“…The direction of the guide field can be freely adjusted as required by experiment using the instrument control software. In particular, this allows a XYZ polarization analysis [37][38][39]. With coils, the sample tilts are limited to ≈ ±5 • .…”

“…Methods for performing the XY Z NPA in such cases were considered in Refs. [37][38][39]. The advanced procedures for full NPA on HYSPEC are currently in development.…”

“…For the full XY Z NPA, at least 3 orientations of neutron polarization on sample have to be measured [37][38][39]. In a polarized neutron experiment on a TAS with narrow, collimated beams, this is usually accomplished by performing measurements using the vertical guide field (VF, P Z) and two mutually perpendicular horizontal field (HF) directions: along the wave vector transfer (P Q) and pependicular to it (P ⊥ Q).…”

“…An alternative approach, which is largely free of these limitations, relies on developing a wide-angle supermirror polarizer (SP) system [1,[33][34][35][36]. Such systems are lowmaintenance, easy to operate, and are weakly sensitive to magnetic fields, thus allowing the XYZ-polarization analysis [37,38]. However, they have a strongly energydependent transmission, which is very low in the thermal to epithermal neutron energy range, thus limiting significantly the neutron energy bandwidth amenable to NPA.…”