Effect of ultraviolet light, solar radiation, XeCl laser and xenon arc lamp on the nuclear track recording properties of CR-39

CR-39 nuclear track detectors were exposed in air to various light sources such as three ultraviolet (u.v.) lamps (λ = 253.7, 300 and 350 nm), a xenon chloride (XeCl) excimer laser (λ = 308 nm), a xenon arc lamp and sunlight. A visible change of colour (yellowing) of detectors under heavy doses was noticed with the first three sources. The exposure to u.v. light sources resulted in degradation of the surface and in an increase of the bulk (V_b) and track (V_t) etch rates at wavelengths of 253.7 and 350 nm, while at 300 nm no such increase was observed. In an attempt to explain this odd behaviour u.v. absorption spectra of CR-39 obtained after exposure to the various u.v. sources were also studied. However, no clear answer emerged. On the other hand, a slight enhancement in detector sensitivity (V = V_t/V_b) was observed for the samples exposed to 253.7 and 350 nm only. At a wavelength of 350 nm different exposure times resulted in different etch induction times. In fact, etch induction time for fission fragments shortened from 28 min for unexposed samples to 2 min in the samples exposed for 86 h and V_b decreased with the depth of the plastic. On the other hand, the exposure to an excimer laser resulted in apparent softening of the surfaces for a cumulative energy density up to 30 J cm^-2 and hardening started from 30 up to 230 J cm^-2. The laser hardening, however, was found to saturate above an exposure dose of 40 J cm^-2. The surface of the detectors was also damaged when exposed to a high dose from a xenon arc lamp. However, for shorter exposure times, the effect was a slight decrease in V_b and V_t. Finally, a controlled exposure to natural sunlight caused an increase of both the V_b and V_t up to 30 h of exposure, and saturation started after that, while no enhancement was noticed in V. Long exposures (2 months) resulted in constant V_b, and increase in V_t and V with etching time.