Slow positron beam production by irradiation of p+, d+, and He2+ on various targets

Slow positron beams were extracted by irradiating various targets with p+, d+ and He2+ ion beams from the AVF (azimuthally varying field) cyclotron of RIKEN. The targets were selected considering the large cross section and high maximum energy of the β+-decay. Two different geometries of the target and moderator (one W sheet) arrangement, reflection-type and transmission-type were used and a yield of ∼ 104 slow e+/s/μA was obtained. However, in both geometries loss of a fraction of the fast positrons by self-absorption in the target is unavoidable. For increasing the number of available fast positrons we have designed a gas target (N2) system. The estimated slow positron yield is 1.5 × 105 e+/s/μA using a 16 MeV proton beam and a one W foil moderator.