Image of measured intensity variation caused by neutron precession in the magnetic field of a simple DC coil. The coil is oriented horizontally along the fringes. The variation of image intensity is shown as a function of TOF (wavelength) for three regions of interest. This can be used to reconstruct the magnetic field of the coil.
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The recent development of fast, highly pixelated neutron detectors capable of performing transmission radiography at a pulsed source, along with 3He spin filters, has opened up a number of interesting new possibilities in polarised neutron imaging from magnetic materials.
For instance, by combining the inherently good energy resolution of a time of flight (TOF) instrument at a pulsed source with high spatial resolution it is possible to perform detailed structural and compositional analysis of complex materials. By the addition of neutron polarisation (provided by polarised 3He spin filters) it also becomes possible to directly image magnetic flux both in vacuum and within materials, akin to using the neutrons as iron filings to show magnetic field patterns. The additional image contrast observed in polarized neutron imaging results from the precession of the neutron spin in a magnetic field, e.g. within the sample.
The amount of rotation depends on the wavelength of the neutron. The good wavelength resolution of a pulsed neutron source (<0.1% Δλ/λ) should produce better resolution than that of a reactor (>1% Δλ/λ). The Crisp reflectometer was used to demonstrate that polarised neutron imaging can be performed at ISIS with these advantages of the TOF technique.
Dr A S Tremsin (University of California at Berkeley), Dr M Strobl (Hahn-Meitner-Institut), Dr C J Kinane, (STFC), Dr S Boag (STFC), Dr R M Dalgliesh (STFC), Dr J Kelleher (STFC)
Research date: August 2011
Contact: Dr A S Tremsin (firstname.lastname@example.org), Dr C J Kinane (email@example.com)
Further reading: A. S. Tremsin et. al., in print, Nucl. Instr. and Meth. A. 652 (2011) 400.
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