70 MeV Carbon C5+ ion induced modification in polystyrene by positron annihilation

Polystyrene is the radiation resistant polymer and occupies a unique position in the study of radiation effects. The bombardment with swift heavy ions (SHI) results in the change of free volume properties which have strong correlation with macroscopic properties of the polymeric material. Positron annihilation lifetime spectroscopy (PALS) provides direct information about the dimension, content and hole size distribution of free volume in polymers. Polystyrene films were irradiated with C5+ ions of energy 70 MeV to fluences of 10(10), 10(11), 10(12) and 10(13) ions/cm(2) from 15 UD Pelletron accelerator at Nuclear Science Centre (NSC), New Delhi, India. The effect of ion irradiation characterized by PALS has been studied. Observed lifetime spectra were resolved into three components and o-Ps lifetime component was associated with the pick off annihilation of positronium trapped by the free volume. o-Ps lifetime, free volume hole radius and the average free volume are found to be decreased on irradiation. The average free volume of the micro-voids decreased from 0.4% to 7.6% for fluences of 10(10)-10(13) ions/cm(2), respectively. (c) 2005 Published by Elsevier Ltd.