The optical filter of the disk chopper spectrometer at NIST

The Disk Chopper Spectrometer at the NIST Center for Neutron Research (NCNR) uses a ‘neutron optical "ltera to remove high-energy neutrons and gamma rays. Nevertheless the measured background at the sample position is time-dependent because of short-wavelength neutrons that get through the optical "lter and the choppers. We explain how this happens. ( 2000 Elsevier Science B.V. All rights reserved.