A new type of neutron chopper for measurements with very slow neutrons

Abstract A description is given of a neutron chopper in which the neutrons when traversing the rotor move in the same direction as the surrounding material. The neutron path in the coordinate system rotating with the chopper is a closed curve, so that the neutrons enter and leave the chopper through the same opening on the periphery of the rotor. A specimen can be placed in the neutron path inside the rotor so that the relative velocity is much smaller than the velocity of the neutron. Thus transmission measurements in the μeV region (about 100 A) are made possible. Inelastic scattering measurements of these almost zero-energy neutrons are discussed as well. The same chopping principle is utilized in another design which can be used as monochromator for 10–30 A neutrons. Transmission and resolution considerations of these devices are presented.