Design of a third axis for the chalk river crystal neutron spectrometer

Abstract

The instrument described is used in conjunction with a twin-axis crystal neutron spectrometer to form a fully automatic, tape programmed, triple axis spectrometer for solid and liquid state studies. The collimated reactor neutron beam impinges on and is reflected from a monochromator crystal. The Bragg reflected monoenergetic neutron beam passes through a 2.5 in. square collimator and strikes the specimen mounted on the crystal spectrometer table. The energy distribution of the neutrons scattered from the specimen is subsequently analysed. The reflected beam collimator can be rotated through an angular range of 120°, followed by the monochromator crystal, rotating at half the collimator's angular speed thus making available a monoenergetic neutron beam of continuously variable and reproducible wavelength. A massive shield is provided around the monochromator crystal as well as various mechanisms which ensure the relative alignment of the reactor neutron beam collimator, the monochromator crystal, the reflected neutron beam collimator and the specimen.