Systematic characterization of a Ne, Ar, Kr rare-gas moderated positron beam and spin polarization measurements

In this work we report on the systematic characterization of a rare -gas moderated magnetically-transported continuous positron beam based on a 22Na radioactive source. The characterization was performed with three different rare -gas solid moderators: Ne, Ar, and Kr. Each moderator was deposited and then thermal annealed at temperature - 35 % and - 30 % lower than the melting point, respectively. Tests of moderation/magnetic transport efficiency of the apparatus have shown a maximum efficiency of 1.8 10-3, 2.0 10-3 and 0.6 10-3 for Ne, Ar, and Kr, respectively. The average longitudinal kinetic energy of positrons was found to be - 0.95 eV, -1.25 eV, and - 0.45 eV for Ne, Ar, and Kr moderator, respectively. The spin polarization measurement of moderated positrons was performed by using the Doppler broadening of the annihilation gamma-rays from positronium formed in oxidized nanochanneled silicon positron/positronium converters. Polarization values of 0.30 +/- 0.01, 0.29 +/- 0.01 and 0.29 +/- 0.01 were found for Ne, Ar, and Kr moderator, respectively.