DEVELOPMENT OF A BEAM OF VERY SLOW POLARIZED MUONS

During the last few decades, a variety of methods has been developed w hich makes use of polarized positive muons as a microscopic probe of t he magnetic properties of condensed matter (muon spin rotation, relaxa tion, resonance, mu SR). Until now, available beams for mu SR studies have delivered 100% polarized muons with energies in the MeV range, re sulting in a deep penetration of the muons into the sample material un der investigation. This presently limits the applications of the mu SR technique to the study of the bulk characteristics of matter. To be a ble to control the implantation depth, a very low energy beam of polar ized muons is being developed at the Paul Scherrer Institute. Very slo w polarized muons (kinetic energy similar to 10 eV, polarization simil ar to 90%) are obtained from the moderation of a high energy muon beam in a thin film of an appropriate condensed gas. These muons can be us ed as a source for a beam of tunable energy between a few tens of eV a nd some tens of keV. Implantation depths in the range of few to a few hundreds of nanometers can thus be achieved by varying the energy.