Polarization measurement of a slow positron beam generated with a compact cyclotron

We measured polarization of a slow positron beam produced in online-manner via the 27Al(p,n) 27Si reaction caused by proton irradiation. The intensity of this beam is measured to be 5105 e+/sec for protons with the energy of 18MeV and the current of 30mA. The polarization measurement makes use of the magnetic quenching of positronium due to Zeeman effect in a magnetic field of a several kG. The polarization of the beam is evaluated to be 38.44.0(statistical)5.8(systematic)%, which is consistent with the estimation based on our Monte Carlo simulations including depolarization processes in matter.