The defect evolution as a function of the annealing temperature has be
en studied in monocrystalline silicon grown in a hydrogen atmosphere a
nd irradiated with 3.6 x 10(17) neutrons/cm(2). Positron lifetime spec
troscopy has been used and the results compared with infrared absorpti
on measurements. Vacancy-H, vacancy-2H, vacancy-O-H and divacancy comp
lexes with m hydrogen atoms (m < 6) have been identified for the first
time as possible positron traps.