Positron Experiments At The New Positron Beam Facility Nepomuc At Frm Ii

The in-pile positron source NEPOMUC of the Munich research reactor FRM II delivers a low-energy positron beam of highest intensity. Different source potentials can be applied in order to vary the primary kinetic energy of the positrons in the range between 15 eV and I keV. The maximum yield of slow positrons is up to 4 x 107 and 5 x 108 moderated positrons per second, respectively. New instruments for beam diagnostics have been implemented for the determination of the positron intensity and for positron beam profile measurements. The long-term stability and the degradation of the platinum moderator as well as the recovery procedure were investigated. In the present arrangement of NEPOMUC's instrumentation the monoenergetic positron beam is magnetically guided to different experiments: a coincident Doppler broadening spectrometer (CDBS) and an analysis chamber for positron induced Auger electron spectroscopy (PAES). In addition, an apparatus for the production of the negatively charged positronium ion was connected to the beam line in order to investigate this bound leptonic system in collaboration with the Max-Planck Institute for nuclear physics. An overview of the beam performance, the current status of the positron beam facility and the experiments is presented. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.