IODINE DIFFUSION AND TRAPPING IN POLYETHYLENE IMPLANTED WITH 150 KEV F+ AND AS+ IONS TO DIFFERENT FLUENCES

Polyethylene samples irradiated with 150 keV F+ and As+ ions to the fl uences of 10(11)-10(15) cm(-2) were exposed to iodine vapour at 90 deg rees C for 4 h and the depth profiles of incorporated iodine were dete rmined using the Rutherford back-scattering technique. For the implant ed fluences less than or equal to 10(13) cm(-2), the iodine content in creases proportionally to the implanted ion fluence, and the average n umbers of iodine atoms incorporated per ion are 5.2 x 10(3) and 1.1 x 10(4) for F+ and As+ irradiation, respectively. For higher implanted f luences the increase in the iodine uptake is much slower and for the h ighest fluences the iodine content even declines. The iodine depth pro files evolve dramatically with increasing ion fluence. For the fluence s less than or equal to 10(14) cm(-2) and both ion species, ''bumpy'' profiles are observed which, at higher fluences, change into ''deplete d'' ones comprising two concentration maxima with no iodine in between . The profile change is due to a gradual degradation of polymer struct ure taking place at higher implanted fluences. A simple phenomenologic al model is suggested describing the profile evolution over the whole range of the fluences used.