PRODUCTION OF SHORT-LIVED POSITRON SOURCES FOR SPIN-POLARIZED POSITRON BEAMS USING A 35 MEV ALPHA-BEAM

Various short-lived positron sources for polarized positron beams have been on-line produced by irradiating nickel, aluminum, and silicon ta rgets for the first time using a 35 MeV alpha beam from the RIKEN AVF cyclotron. The beta(+) rays emitted from the targets with wide energy spread are converted to a monochromatic slow positron beam using a 10 mu m tungsten polycrystalline moderator. In the current stage, similar to 10(4) e(+)/(s mu A) can be obtained from nickel and aluminum targe ts, which is in relatively good agreement with the calculated slow pos itron yield. For silicon, a relatively low slow-positron intensity, si milar to 10(3) e(+)/(s/mu A) was Obtained probably due to the charge u p effect in the silicon surface during irradiation. For increasing the slow-positron yield loss of fast positrons in the material must be av oided, and as a new means for such improvement it is proposed to use g as targets.