Polycapillary focusing optic for small-sample neutron crystallography

Abstract

The relatively low¯ux from neutron sources means that structural analysis using neutron diffraction requires large crystals that are often not available. The feasibility of a polycapillary focusing optic to produce a small intense spot of size < $0.5 mm for small crystals has been explored and such an optic has been tested both on a monochromatic and on a polychromatic beam. In a diffraction measurement from an -quartz crystal using a 2.1 convergent beam from a pulsed neutron source, six diffraction peaks in the 1.5±4 A Ê wavelength bandwidth transmitted by the optic were observed. These diffraction spots show an intensity gain of 5.8 AE 0.9 compared with a direct beam diffracting from the same sample volume as that illuminated by the convergent beam.

X-ray optics: an enabling technology for science, medicine, and industry

“…The diffracted-beam intensity gain depends on the input neutron-wavelength-spectrum and the input neutron angular-distribution. Diffraction measurements with convergent neutron beams at the Single Crystal Diffraction (SCD) instrument on the Intense Pulsed Neutron Source (IPNS) at Argonne National laboratory have shown diffracted-beam intensity gains of 10-100 46,47 . These were for crystals with small lattice spacing, not as well suited for the transmission spectra of polycapillary focusing optics (typically in the 2-5 Å wavelength range) so only a few diffraction spots could be observed.…”

“…Of great scientific importance is the potential use of convergent neutron beams for protein crystallography 46,47 . Since neutrons scatter from nuclei rather than from electrons, as do x-rays, neutron diffraction can provide important additional information on protein structure and dynamics.…”

Focusing neutrons with tapered capillary optics

“…3 Both techniques have been combined in recent measurements 4 to profile small-scale ͑Ϸ100 m͒ compositional variations in materials. Finally, preliminary measurements 5 have been taken for the use of the monolithic lens for small-sample neutron crystallography.…”

“…6 This lens has been used for increasing the neutron current density on a small crystal sample for preliminary tests of the quasi-Laue technique for crystallography on a pulsed source. 5 The lens consists of a single piece of fused boron glass of a hexagonal cross section, with the distance between the flats of 7.36 mm at the entrance and 5.60 mm at the exit. The length of the optic is 75 mm.…”

Compound Refractive Lenses for Thermal Neutron Applications

“…If a neutron does not strike the steep wall between zones, it will refract just as for a parabolic lens. As shown in Adelphi's patent for Fresnel CRLs [17], ignoring losses to the walls, each zone must be about twice the median misalignment to preserve the transmitted intensity and resolution is not significantly affected by misalignment. Essentially, the effective aperture is reduced when there is random variation of the unit lenses off the average optical axis of the lenses, but that there is no other degradation to image quality or efficiency [14].…”