POSITRON PRODUCTION BY GAMMA BEAM AT ELI-NP

We propose to obtain an intense beam of moderated positrons (4) with an intensity of the primary positron beam of 1 x 10(6) - 2 x 10(6) e(s)(+)s(-1) by the (gamma, e(+)e(-)) reaction using an intense gamma-beam of 2.4 x 10(10) gamma s(-1) with energies up to 3.5 MeV. Using fully circularly polarized gamma-beam we aim to obtain an intense, polarized positron beam with a polarization degree of 31-45%. Higher degree of polarization would also be possible with reduced beam intensity. The beam will be transported to different detector systems through beam lines, via solenoidal magnetic fields. Polarized positron beams open up a totally unexplored research area in applied physics studies of Fermi-surfaces, defects, interfaces etc., where polarized electrons can be studied. A simple, fast scintillator detector system for gamma-induced positron annihilation lifetime spectroscopy for studies of bulk samples is proposed. The ELI-NP facility will be user-dedicated and unique for positron research in the Eastern Europe. It will provide a simple source setup, with easy access for upgrades of the converter/moderator assembly toward more sophisticated setups, providing a more intense and brighter positron beam. The beam will have the world highest intensity of polarized positrons for material science studies and, therefore, it will become a unique tool for the investigation of magnetic samples.