Development of moderators for high efficient positron

This study aims at investigation on highly efficient moderators and their optimum treating conditions as well as elucidation on behavior of positron in solid and at its surface In 1998 fiscal year, together with operation of investigation on moderators at electrostatic type positron beam apparatus, a new experiment at magnetic field type beam apparatus was initiated. As a result, on evaluation at electrostatic type beam apparatus, it was elucidated that among evaluated moderators tungsten single crystal foil showed the best results in efficiency as well as in mono-chrome and that heat treatment was important for the single crystal foil. Tungsten multi-crystal foil is inferior in it property to that of its single crystal foil, but can be said to be sufficiently actual on consideration of its easy availability, and its easy handling. And, on measurement of simultaneous annihilation gamma-ray Doppler width using the magnetic field induced type beam apparatus, investigation in this fiscal year remained only at initiation, but this seemed to be much effective not only from a viewpoint of a high efficient moderator development but also for a method to obtain some informations on behavior of positron in a material. (G.K.)