Polarization-Analyzed Small-Angle Neutron Scattering with an $\textit{in-situ}$ $^{3}$He neutron spin filter at the China Spallation Neutron Source

TL;DR

This paper reports the first successful implementation of polarization-analyzed small-angle neutron scattering (PASANS) at the China Spallation Neutron Source, utilizing an in-situ $^{3}$He neutron spin filter to enhance magnetic scattering studies.

Contribution

It introduces a novel PASANS setup at CSNS with an in-situ $^{3}$He neutron spin filter and a comprehensive data reduction method for pulsed neutron beams.

Findings

Successful demonstration of PASANS at CSNS

Validated data reduction method with silver behenate sample

Achieved momentum transfer coverage of ~0.25 Å$^{-1}$

Abstract

Polarization-analyzed small-angle neutron scattering (PASANS) is an advanced technique that enables the selective investigation of magnetic scattering phenomena in magnetic materials and distinguishes coherent scattering obscured by incoherent backgrounds, making it particularly valuable for cutting-edge research. The successful implementation of PASANS in China was achieved for the first time at the newly commissioned Very Small Angle Neutron Scattering (VSANS) instrument at the China Spallation Neutron Source (CSNS). This technique employs a combination of a double-V cavity supermirror polarizer and a radio frequency (RF) neutron spin flipper to manipulate the polarization of the incident neutrons. The scattered neutron polarization is stably analyzed by a specially designed $\textit{in-situ}$ optical pumping $^{3}$He neutron spin filter, which covers a spatially symmetric scattering angle coverage of about 4.8 $^{\circ}$. A comprehensive PASANS data reduction method, aimed at pulsed neutron beams, has been established and validated with a silver behenate powder sample, indicating a maximum momentum transfer coverage of approximately 0.25 {\AA} $^{-1}$.