Energy Selective Neutron Imaging

Spectrum of the ICON cold neutron imaging beamline and NEUTRA thermal imaging beamline, together with the theoretical microscopic cross-section for the iron bcc and fcc phases
Spectrum of the ICON cold neutron imaging beamline and NEUTRA thermal imaging beamline, together with the theoretical microscopic cross-section for the iron bcc and fcc phases

Energy-selective neutron imaging exploits the wavelength-dependent behaviour of the materials cross-section σ(λ) as a new source of image contrast. 

Many polycrystalline materials’ cross section exhibit sharp edges, so-called Bragg edges. Imaging around these Bragg edges offers a.o.:

  • Increased contrast between materials or phases, as they exhibit different Bragg edge positions
  • Increased material penetration, by selecting wavelengths of low material cross-section
  • Increased material content quantification, by imaging in the long wavelength absorption range where little scattering contributions are present.
  • Qualitative texture mapping, as different textures emphasize different Bragg edges.

A prerequisite for energy-selective imaging is a cold neutron spectrum (λ ≥ 2.5Å) - as this is where the most dominant Bragg edges appear – and a monochromator for energy-resolution. Both are available at the ICON beamline, with the beam port looking at the 25K cold neutron source and an integrated neutron velocity selector offering Δλ/λ = 15% monochromaticity. Development of a second monochromator for reaching Δλ/λ = 5% is ongoing.