High-frequency modulation of a monochromatic neutron beam

A new method for modulating a monochromatic neutron beam is described: The neutrons are first polarized, and then the direction of the polarization vector is periodically changed by the high-frequency magnetic field in the so-called meander coil. The angle, by which the polarization vector is turned, is the modulation signal. As this modulation is produced without the aid of moving parts, high modulation frequencies are attainable. A meander coil operating at a frequency of about 750 kHz is described in some detail, and the results of test measurements carried out at the high-flux reactor of the Institut Laue-Langevin in Grenoble, France, are reported. The meander coil was developed for an experiment in which the velocity of neutrons (≈1600 ms−1) was measured with a relative uncertainty below 10−7.