Polarization measurements in neutron imaging

Abstract

While neutron imaging is a wellestablished technique for investigations of inner structures and processes in materials, complex systems, and devices, the utilization of polarized neutron beams to visualize magnetic phenomena has been introduced only about a decade ago. In contrast to neutron scattering studies, where the interaction of the neutron's magnetic moment with magnetic states of matter has been exploited for a long time, the direct visualization of magnetic fields in neutron imaging is a relatively new field and is still developing. Here, we give an overview of the status and provide approaches to visualizing magnetic fields with polarized neutrons, together with a report on the latest developments in attempting to record neutron tomographies for 3D reconstructions of magnetic vector fields.

Scalable Neutron Imaging Systems at Compact Sources

“…It is very often such applications that offer a unique way to demonstrate to the common taxpayer as well as to funding agencies the high potential and manifold usefulness of neutron-based techniques starting at flux levels as low as 1000 n/cm 2 s. Outstanding examples are the developments for time-offlight imaging at JPARC performed at HUNS in Hokkaido, including sophisticated techniques like polarized neutron imaging [15]. Another example might be the test beamline for ESS in Berlin supporting the development of a sophisticated wavelength frame multiplication chopper system not only for neutron imaging [16].…”

Full-field neutron microscopy based on refractive optics

“…As an example, consider imaging with polarized neutrons, where the polarization analyser equipment requires an extended distance of, say, 0.5 m between the sample and the detector. As typical parameters for such measurements today (Strobl et al, 2019) we shall consider imaging of a sample of dimension 2 cm. Using an energy bandwidth of 3% (given by the spin precession resolution), a spatial resolution of 500 mm is achievable, corresponding to a divergence of the incoming beam of 1 mrad.…”

“…With such beams, it is natural to base bright-field imaging studies on placing a 2D detector downstream of but in close proximity to the sample. This approach enables a large variety of contrast to be explored, including attenuation contrast (Kallmann, 1948;Strobl et al, 2009), phase contrast (Strobl et al, 2008) and more specialized techniques such as spectral imaging (Lehmann et al, 2014), Bragg edge contrast for mapping of stresses (Santisteban et al, 2001) and phases (Steuwer et al, 2004;Woracek et al, 2014), extinction contrast for mapping of large grains (Cereser et al, 2017), and some versions of polarized neutron imaging for visualizing magnetic field distributions (Sales et al, 2019) and magnetic domains (Kardjilov et al, 2008;Schulz et al, 2010;Strobl et al, 2019;Jorba et al, 2019).…”

Visualization and quantification of inhomogeneous and anisotropic magnetic fields by polarized neutron grating interferometry

“…On the other hand, real-space data, such as the one retrieved by neutron imaging measurements, can resolve macroscopic structures. Utilizing polarized neutrons, neutron imaging has proven to be a powerful tool for retrieving spatially resolved information about magnetic field distribution 7,8 . Imaging with polarized neutrons has progressed in recent years and different methods have been developed, capable of analyzing and directly visualizing local magnetic interactions 9 .…”

“…Imaging with polarized neutrons has progressed in recent years and different methods have been developed, capable of analyzing and directly visualizing local magnetic interactions 9 . The technically simplest realization of neutron imaging with a polarized beam is called neutron depolarization imaging (NDI) 7,8,10 . It enables to investigate whether the magnetic sample contains non-parallel field components with respect to the initial beam polarization, which cause depolarization effects in the neutron beam.…”