RF neutron spin flippers in time of flight Spin-Echo Resolved Grazing Incidence Scattering (SERGIS)

S.R Parnell,A.A Van Well,R.M Dalgliesh,N.J Steinke,J Plomp

doi:10.1088/1742-6596/1021/1/012040

S.R Parnell, A.A Van Well + Show 3 more

Open Access

https://doi.org/10.1088/1742-6596/1021/1/012040

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Abstract

RF coils have been routinely used for Larmor labelling on the Offspec instrument at ISIS. These coils encode directional information via the neutron polarization using a series of parallelogram-shaped pole shoes which can be tuned to different angles with an RF gradient flipper in the centre of each magnet. We report on measurements of the magnetic field integral through the coils in reflection geometry for a range of scattering angles and different pole shoe angles. Such information is mapped out by measuring the phase of the neutron polarisation and the measurements are discussed in light of data on patterned silicon gratings with a dewetted polymer and the visibility of in-plane structures to SERGIS.

Highlights

In typical neutron scattering experiments information on the sample under investigation is obtained via measurement of the momentum transfer (Q) and/or the energy change of the neutron
Scattering angle encoding involves shaped magnetic fields such that the accumulated Larmor precession is dependent upon the spatial trajectory of the neutron
The shaped field regions perform the angle encoding and are arranged with opposite magnetic field, in the case of an unscattered neutron it traverses both magnetic fields and the Larmor phase added in the first magnet is cancelled by the second magnet for all possible angles φi

Summary

Introduction

In typical neutron scattering experiments information on the sample under investigation is obtained via measurement of the momentum transfer (Q) and/or the energy change of the neutron. The shaped field regions perform the angle encoding and are arranged with opposite magnetic field, in the case of an unscattered neutron it traverses both magnetic fields and the Larmor phase added in the first magnet is cancelled by the second magnet for all possible angles φi Whereas if it is scattered the resulting path difference results in a different Larmor phase which varies with the strength of the magnet and the degree of scattering is measured in the change in Pse. As discussed in [10] the same Lamor phase encoding can be achieved using a series parallelogramshaped precession regions with flippers in the centre of each magnet. It is necessary to correct for these integral changes as a function of λ, θ0 and θf

Measurement of the field integral as a function of scattering angle

Discussion and conclusions