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 ve ctor 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 derail, and the results of test measurements carried out at the high-flux reactor of t he Institut Laue-Langevin in Grenoble, France, are reported. The meander co il was developed for an experiment in which the velocity of neutrons (appro ximate to 1600 ms(-1)) was measured with a relative uncertainty below 10(-7 ). (C) 2000 Elsevier Science B.V. All rights reserved.