Development of spin-polarized slow positron beam using a 68Ge–68Ga positron source

A 68Ge–68Ga positron source was produced from the 69Ga(p, 2n)68Ge nuclear reaction by irradiating a GaN substrate with 20 MeV protons. Fast positrons from the source were converted to slow positrons using tungsten meshes and foils and were then electrostatically transported to the sample chamber. The spin polarization of the positron beam was determined as 47 ± 8% from the magnetic field dependence of the para-positronium intensity in fused silica. The Doppler broadening of the annihilation radiation spectra of polycrystalline Fe showed asymmetry upon field reversal. The spin-polarized positron beam generated by the 68Ge–68Ga source may be applicable to study the magnetic properties associated with surfaces, interfaces, and thin films.