New physics with intense positron beams
A. Dupasquier, Department of Physics, Politecnico di Milano
The aim of this seminar is to present an overview of the current research based on positron beams and to discuss the latest achievements and the new opportunities made possible by recent progress in the construction of intense beams. Positron beams with energies tunable below a few tens of keV are used since more than 25 years for the study of surfaces and sub-surface defects. Laboratory positron beams are based on sealed radioactive sources of β+ isotopes (typically, less than 100 mCi of 22Na) and deliver fluxes between 104 and 106 e+/s at the target. Much higher fluxes can be achieved by using brighter positron sources based on pair production by gamma from brehmsstrahlung or from nuclear decays. Three facilities exist in the world (one at a LINAC, two at reactors) and a few more are under construction which produce positron fluxes above 108 e+/s. Even higher instantaneous fluxes can be achieved by accumulating moderated positrons in a Malmberg-Penning trap and delivering them on the target in nanosecond pulses. High flux beams open the way not only to incremental progress in old physics (essentially materials science) but to a jump into new physics with anti-matter. Production of anti-hydrogen and of positronium molecules are recent achievements, next steps will probably be anti-matter gravity, positron annihilation gamma lasers, BEC condensation of positronium.