Physics with Positrons

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Our research encompasses the development of forefront instrumentation using positrons and the application of positron beams in a wide variety of fields ranging from fundamental physics via solid state and surface physics to applied materials science. By exploiting neutron capture gamma rays and subsequent pair production we generate the worlds most intense monoenergetic positron beam at NEPOMUC at the FRM II. The positron beam facility at NEPOMUC hosts various instruments (CDBS, TRHEPD, PAES, PLEPS, SPM, OP) open to external scientific users.

We apply (coincident) Doppler broadening spectroscopy of the annihilation photons to investigate open-volume lattice defects and precipitates. Our positron µ-beam at the CDB spectrometer allows 3D-imaging of defect distributions in all kind of materials. By using ²²Na-based setups in the lab we apply positron annihilation lifetime spectroscopy (PALS) in order to study type and concentration of defects in crystalline solids as well as the free volume of polymers. The depth dependent positron lifetime is measured with PLEPS at NEPOMUC. Surface analysis with topmost layer sensitivity is performed via high-energy positron diffraction (structure) or by the detection of positron annihilation induced Auger electrons (element distribution). The bulk electronic structure is studied by the measurement of the angular correlation of the gamma radiation emitted from annihilation of electrons with (spin-polarized) positrons.

In collaboration with external groups we carry out fundamental experiments; examples are: determination of the decay rate of the Ps^– (Ps negative ion), velocity measurement of cold Ps, development of efficient e⁺-Ps converters for antihydrogen production, and setting up a magnetic trap for simultaneous storing of positrons end electrons aiming to produce the first pair-plasma.