A time-of-flight spectrometer for elastic neutron scattering on powdered samples

Overview & Synopsis

A time-of-flight spectrometer especially built for the study of powdered samples with complex surroundings, such as a high-pressure cell (up to 35 kbars) and a high-temperature furnace (up to 2 500 °C) is described. A correlation chopper is used to decrease the time-independent background due to the high epithermal flux in the incoming beam. The chopper slots are distributed according to a pseudo-random binary feedback shift register sequence of 511 elements, the elementary neutron pulse being 8 μs in width. The geometry has been optimized in order to reach a high resolution : Δd/d values of 0.75 % at d = 1 A and 0.4 % at d = 3 Å are obtained. Structure refinements on test samples with simple structure (UO2 give a reliability factor R of 1.3 % which compares fairly well with the results of the high resolution fixed-wavelength goniometer, D1A at the Institut Laue-Langevin.