Two-dimensional angular correlation positron studies of large voids in aluminium

Abstract

The authors have measured the two-dimensional angular correlation of positron annihilation radiation from single crystals of aluminium containing voids and other defects. No asymmetry was found between the (110) and the (100) directions for angles less than 10 mrad. This is contrary to what one expects if positrons are trapped in extended surface states on the void walls, which are primarily (111) planes. A tentative hypothesis involving positronium states in voids is offered.