GENERATION OF VERY SLOW POLARIZED MUONS BY MODERATION

At the Paul Scherrer Institute very slow, nearly 100% polarized, posit ive muons with an energy of similar to 10 eV are produced by moderatin g a secondary beam of surface muons in a thin film of an appropriate c ondensed gases. These epithermal muons can be used as a source of a te rtiary beam of tunable energy between similar to 10 eV and similar to 20 keV. Such a beam allows the mu SR technique to be extended to the s tudy of thin films and surfaces. In order to be able to perform time d ifferential mu SR experiments we have developed an ultra-thin detector that registers the passage of keV muons and permits to trigger the ex periment. The results achieved so far demonstrate that first investiga tions of thin film samples can be performed with the present set-up.