CONSTRUCTION OF POLARIZED SLOW-POSITRON BEAMS USING A COMPACT CYCLOTRON

We have constructed a polarized positron beam using positrons provided from the beta(+) decay of Si-27 With the half-life of 4.1 s and the m aximum beta(+) energy of 3.85 MeV. This isotope is produced via the Al -27(p, n)Si-27 reaction caused by proton irradiation using a compact p roton cyclotron. The intensity of this beam is measured to be 5 x 10(5 ) e(+)/s for protons with the energy of 18 MeV and the current of 30 m u A. A pair of Monte Carlo simulation programs has been developed to c alculate depolarization of positrons in our beam channel. One program simulates spin motion of the positron under electric and magnetic fiel ds, while the other simulates depolarization due to multiple Coulomb s cattering in matter. Using these simulators, we designed a special pol arimeter by means of magnetic quenching of ortho-positronium and measu red a quenched lifetime of ortho-positronium under the magnetic field of 0.4, 2.5 and 4.0 kG leading to the average polarization of 33.4 +/- 5.3%, which is consistent with the estimation based on the Monte Carl o simulations.