Polycapillary focusing optic for small-sample neutron crystallography

J. Appl. Cryst. (2002). 35, 677–683

The image of the focused beam using a tapered monolithic lens with cold neutrons. The focal spot at the center is about 100 μm wide. Both the shadow of the hexagonal cross section of the optic and the background halo of neutrons passing through the optic and inside the collimator are concentric around the focus when the optic is aligned with the incident beam. Photos of the lens interior entrance cross section and exterior are also shown.

The relatively low flux from neutron sources means that structural analysis using neutron diffraction requires large crystals that are often unavailable. Recent demonstrations of convergent beam electron and x-ray diffraction have motivated the use of polycapillary optics for small-sample crystallography using convergent neutron beams. We have examined the use of a focusing optic for diffraction of both monochromatic neutrons at the NIST research reactor and for time-of-flight polychromatic neutrons at the Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory. The convergent beam method (CBM) promises advances for crystallography on small samples (less than 500 μm) of small- to medium-size molecules at extreme pressures and temperatures, for proteins (as demonstrated for x-rays), and for strain and texture mapping of polycrystalline samples.