POSITRON-ANNIHILATION AND DIFFRACTION STUDIES OF THE PHOTOPOLYMERS BASED ON THE ACRYLATE OLIGOMERS

Positron annihilation lifetime and X-ray; diffraction measurements wer e made on photopolymers based on acrylate oligomers. Polymerization wa s caused by exposure to ultra violet light. The measurements were made on photopolymer specimens with different ultra violet light exposure limes. The longest positron lifetime, tau(3), was associated with the pickoff annihilation of orthopositronium (o-Ps) trapped in voids. Inte ratomic distances and coordination numbers for the investigated sample s have been determined From X-ray data. Ultra violet light exposure ti me affects mainly the sizes of the voids. The nearest neighbour distan ces and coordination numbers are independent of the ultra violet expos ure time. (C) 1998 Elsevier Science B.V. All rights reserved.