Novel Neutron imaging modalities

Three-Dimensional Polarised Neutron Tomography (3DPNT)

Neutrons are charge-less particles. However, they have a magnetic moment with the direction defined by the neutron spin. A neutron travelling through an external magnetic field will experience a torque such that the neutron spin will precess in the external magnetic field.

We put this neutron sensitivity to external magnetic fields to use with the novel technique: Three-Dimensional Polarised Neutron Tomography (3DPNT), which we are developing in order the measure the three dimensional magnetic fields inside bulk samples of various kinds. Such information has hitherto been unattainable and thus our techniques open up the possibility for unique investigations of material properties in a wide range of fields from energy materials to super conductors.

The technique is being developed for use at high power neutron spallation sources, such as the future European Spallation Source, with the utilisation of the Time-of-Flight information of the pulsed neutron beam in mind.

The figure shows the results from the 3DPNT measurement at J-PARC, Japan, of a current carrying solenoid, with the structural signal on the left and the three components of the magnetic field on the right, clearly depicting the main magnetic field along the solenoid axis as well as the smaller magnetic field components around the edges of the solenoid openings.

See also Three Dimensional Polarimetric Neutron Tomography of Magnetic Field, M. Sales et al. Sci. Rep. (2018) 8:2214 DOI:10.1038/s41598-018-20461-7

Three-Dimensional Neutron Diffraction (3DND)

This technique focuses on the non-destructive characterization of the crystalline microstructure in the bulk of materials, where the position, shape and crystallographic orientation of the individual crystals (grains) can be observed. In the feasibility study shown in the figure to the left a 1 cm iron bar has been measured at J-PARC in Japan. In total, 108 grains where reconstructed. The red volume in the top part of the sample consists of an ensemble of randomly oriented grains with size of a few microns. Although the characteristics of the individual small grain cannot be observed, still the neutron time-of-flight data enables reconstruction of the spatial coverage of the small grains, thus facilitating multiscale characterization.

See also Time-of-Flight Three Dimensional Neutron Diffraction in Transmission Mode for Mapping Crystal Grain Structures, A. Cereser et al. Sci. Rep. (2017), 10.1038/s41598-017-09717-w


Søren Schmidt
Samarbejde med Henning Friis Poulsen
DTU Fysik