Neutron Optics
App. Note 501 – X-ray Neutron System
The properties of capillary technology allow polycapillary optics to control and focus neutrons as well as X-rays. Neutrons can be focused into a small spot resulting in an increased neutron current density on the sample. The principle behind these optics is the convergence of a parallel beam of neutrons to a point through multiple total-external reflection of neutrons along the smooth inner walls of the capillary channels. Such optics are useful for applications including single crystal and powder neutron diffraction studies, as well as high spatial resolution studies of strain, phase, and texture distribution in extended samples.
Focal spot size depends on the neutron wavelength and the output focal distance of the optic. Polycapillary optics can provide large gains over conventional unfocused neutron beams. Intensity gain is dependent on the neutron wavelength spectrum and the angular distribution from the source, as well as the input area and the output focal distance of the optic. Gains of 5-100x have been measured in the single crystal diffraction (SCD) beam-line at the Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory. Gains up to 500x have been achieved on the general purpose powder diffractometer (GPPD) at IPNS.
Characteristics of Neutron Optics:
| Type | Beam Focusing, Polychromatic |
| Useful Neutron Wavelength Range | Typically 1.5 – 5 Å |
| Adjustable Beam Convergence | 0.5 – 4.5 degrees |
| Working Distance | Typically 50 mm |
| Focused beam size | 50 – 500 μm (depending on neutron wavelength and optic working distance) |
| Intensity Gain (Compared to conventional unfocused neutron beams) | 5 – 500x (depending on neutron wavelength spectrum, source angular distribution, optic input area and working distance) |