Abstract: In order to make possible precisely controlled and reliable operation of the rotors of a neutron chopper each rotor is to be driven by a hysteresis motor, whose rotor is in the form of a hollow cylinder. The attachment of each drive rotor to the one end of the rotor is by way of a non-magnetic disk or ring which is screwed to the lower end of the rotor or the top end thereof in accordance with the design. The drive rotor is only shrunk onto the disk or ring. The stator placed around the drive rotor is embedded within the neutron chopper housing in an electrically insulating cast material which is not affected by high vacuum and radiation.