Production of short-lived positron sources for spin-polarized positron beams using a 35 MeV α-beam

Various short-lived positron sources for polarized positron beams have been on-line produced by irradiating nickel, aluminum, and silicon targets for the first time using a 35 MeV alpha beam from the RIKEN AVF cyclotron. The β+ rays emitted from the targets with wide energy spread are converted to a monochromatic slow positron beam using a 10 μm tungsten polycrystalline moderator. In the current stage, ∼ 104 e+/(s μA) can be obtained from nickel and aluminum targets, which is in relatively good agreement with the calculated slow positron yield. For silicon, a relatively low slow-positron intensity, ∼ 103 e+/(s/μA) was obtained probably due to the charge up effect in the silicon surface during irradiation. For increasing the slow-positron yield loss of fast positrons in the material must be avoided, and as a new means for such improvement it is proposed to use gas targets.