Positron beams from small accelerators and status of a novel positron storage project

Positrons are generated by an intense beam of deuterons. Deuterons with energies up to 3 MeV and 300 μA intensity or 1000 W power are guided onto a carbon target. The (d,n) reaction converts 12C into the positron emitter 13N. In one version a CVD diamond target is rotated behind a W foil moderator after irradiation. Rapid heating of the diamond and defect generation limits this method to deuteron power <100 W. At higher power 13N molecules are released had must be condensed behind a moderator. Graphite is employed for higher power doses. External direct current or e-beam heating are used to reach temperatures in excess of 2000 K when nitrogen is released from graphite. Efforts to maximize the release of 13N containing molecules as well as the goal to accumulate positrons in a novel trap design are discussed. Up to 75% of the activity was released at 2 MeV. This decreases with deuteron energy.