Slow positron production using the RIKEN AVF cyclotron

Using the RIKEN AVF cyclotron, various targets were irradiated with proton or deuteron beams to produce β+-decay radioisotopes. Slow positrons are extracted backward at an angle of 30° to the incident ion beam using a well annealed W film, with a thickness of 10 μm, as a moderator. This geometry was chosen to allow for both the use of various kinds of target materials and the in-beam slow positron extraction during ion beam irradiation. In preliminary experiments, a slow e+ intensity of ∼5.6 × 104 e+/s was obtained from BN by irradiating protons with an energy of 14 MeV and a current of 4 μA. From an Al target irradiated with a proton beam with an energy of 10 MeV and a current 3.6 μA, a slow e+ intensity of ∼5.5 × 102 e+/s was also obtained. By irradiating a deuteron beam with 8 MeV energy and 1.3 μA current, slow e+ intensities of ∼4.2 × 103 e+/s and ∼3.4 × 103 e+/s were obtained from carbon and Si3N4 respectively. Using a pulsed ion beam, background noise was eliminated almost completely in three-coincidence measurement.