Development of spin-polarized positron source using high energy proton beam

Maekawa, Masaki; Fukaya, Yuki   ; Yabuuchi, Atsushi; Kawasuso, Atsuo

Using spin-polarized positrons, the excess spins in magnetic substances can be detected. For efficient measurements with spin-polarized positrons, a strong enough source emitting highly polarized positrons is needed. For this purpose, we focus on a Ge radioisotope. This radioisotope decays to Ga with a half-life of 280 days. The endpoint positron energy is 1.9 MeV and hence the theoretical longitudinal spin polarization is approximately 94%. This radioisotope can be produced though the nuclear reaction of Ga (p,2n) Ga. In this study, we report the production of Ge by proton irradiation. We examined a metal form Ga stable isotope and a GaN substrate as target materials. When the metal Ga targets were used, the production rates of Ge were 0.16 and 0.14 MBq/A/h for 20 and 25 MeV, respectively. Using the GaN target, it was 0.24 MBq/A/h. Thus, Ge radioisotopes were generated in both targets. The spin polarizations of positrons emitted from Ge and Na were estimated to be approximately 90% and 30%, respectively.