Upgrade of the Cold Neutron Imaging Instrument, Phase Grating Roll Alignment System

The NIST neutron imaging team, in the Radiation Physics Division of the Physical Measurement Laboratory, is developing a far-field grating neutron interferometer to measure the projection of the pair correlation function, G(Z), of a sample of interest. This interferometer geometry requires precision alignment of 3 gratings about the roll direction of the neutron beam.

Since G(Z) is a vector quantity, aligned perpendicular to the grating direction, the grating alignment stages need to be able to rotate a full 360°, with high resolution. The gratings are lines etched into silicon wafers, where the period of the lines is of order 1 micrometer and the wafers are 100 mm in diameter.

The mass of a grating, including a holder is of order 100 g. The interferometer pattern is measured by translating one of the gratings, so that that mass of the alignment system must be kept to as low as achievable. For control hardware, the separation of two of the gratings along the beam ranges from 1 mm to 300 mm.

The third grating is separated by up to 5 m. The overall grating alignment system requires translating the gratings in the vertical direction, requiring that the grating roll stages (which much also translate) be less than 1 kg in mass. This procurement is to obtain quantity three high precision rotation stages (resolution better than 0.00005 degrees) with a clear aperture to allow the beam to pass unattenuated and required cabling, control hardware, and control software.