A Bent Crystal Neutron Spectrometer and Its Application to Neutron Cross-Section Measurements

The high neutron fluxes now available as a result of the development of chain reacting piles has made it possible to obtain monoenergetic neutron beams of considerable intensity by the method of crystal diffraction. One of the first practical applications of this method has been in the study of neutron resonance cross sections for low energy neutrons.To increase the useful intensity and hence the energy range over which measurements can be made with good resolution, we have adapted the Cauchois type bent crystal spectrometer for use in neutron diffraction. The instrument gives good resolution of neutron resonance peaks of about 0.1 ev width at half maximum at energies up to 1 ev and work can be done at higher energies with a corresponding loss in resolution. As samples of work done with this instrument, absorption measurements on cadmium and iridium are discussed.