Neutron bandpass limiting chopper

摘要

A neutron bandpass limiting chopper consisting of up to four discs and a slow neutrons wiper is described. It produces pulses rid of contamination by unwanted slow neutrons. The basic disc works as a single disc chopper and largely defines the TOF resolution. The widths and positions of the slots in an additional disc define the neutron bandpass. The wiper eliminates slow neutrons with wavelengths beyond the working range and can be designed not only as plates connecting the discs, but also as ribs attached to the basic disc, or else as a rotor with blades on one shaft with the basic disc. The TOF resolution can be varied by using constant width slots in the basic disc and moving the chopper as a whole to change the effective disc radius. Two supplementary discs can also be used, one phased with the additional disc to optimize TOF measurements with the detector at different positions and the other phased with the basic disc to vary the TOF resolution. Application of the bandpass limiting choppers in neutron reflectometers at steady flux reactors is considered.