Time-of-Flight Spectroscopy at the NIST Center for Neutron Research

Abstract

The time-of-flight method has a long and distinguished history. In one form or another it has been in use at the National Institute of Standards and Technology (NIST), formerly known as the National Bureau of Standards, since 1970. The current incumbent is the Disk Chopper Spectrometer (DCS) [1], a direct geometry machine with an optical filter and cooled graphite filter, seven disk choppers, a sample stage, and 913 non-position-sensitive detectors. Slots of different widths in the pulsing and monochromating choppers enable the user to choose among three distinct intensity/resolution conditions without having to change the wavelength or chopper speeds. In practice the high resolution option is not used because the beam does not have sufficient intensity. On the other hand we have used the narrowest (1.35°) slots in the choppers closest to the sample, with the remaining choppers stopped, for pulsed white beam transmission measurements (e.g. ref. [2]) and for Laue diffraction measurements (to determine the orientations of single crystals of helium grown in situ).