Gamma-induced modification on optical band gap of CR-39 SSNTD

Effect of gamma irradiation on optical absorption of nuclear track detectors such as CR-39 was studied in different absorbed doses using ultraviolet-visible (UV-VIS) spectroscopy. The existence of the peaks, their shifting and broadening as a result of gamma irradiation have been discussed. The width of the tail of the localized states in the band gap (Eu) was evaluated using the Urbach edge method. Finally the indirect and direct band gaps in pristine and gamma irradiated CR-39 have been determined. The values of the indirect band gap have been found to be lower than the corresponding values of the direct band gap. A decrease in the optical energy gap with increasing gamma absorbed dose can be discussed on the basis of gamma-irradiation-induced defects in CR-39. The correlation between the optical band gap and the number of carbon atoms in a cluster with the modified Tauc's equation has been discussed in the case of CR-39. © 2008 IOP Publishing Ltd.