Long-term passive monitoring of solar UV radiation using radiochromic films

Abstract

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.The solar ultraviolet (UV) spectrum spans over a range of wavelengths, namely, UVA (315–400 nm), UVB (280–315 nm) and UVC (100–280 nm). The UV radiation reaching the surface of the Earth comprises of mainly UVA, a small amount of UVB and essentially no UVC. Solar UV can affect the human health. An under-dose will lead to diseases such as rickets and osteoporosis, while an over-dose will cause sunburns, skin cancers and cataracts. It is therefore pertinent to design methods for integrated long-term measurements of UV radiation (e.g., over 1 day). Recently, we succeeded in demonstrating the feasibility of using the Gafchromic EBT3 radiochromic film to quantify solar (UVA+UVB) exposures (in Jcm-2). These radiochromic-film products were originally developed for clinical dosimetric applications, with visible-light absorption changes upon X-ray irradiation, but were understood to be also responsive to UV radiations. We found that the usable range of UV exposures for the EBT3 film was from ~0.2 to ~30 Jcm-2. However, the maximum UV exposure could reach 50 Jcm-2 per day, so we need a wider usable range. The current work proposed modifications to the EBT3 film for longer-term measurements (e.g., over 1 day). We explored the UV responses of EBT3 films covered with 2 and 5 barriers, each barrier being a blue polypropylene film with a thickness of 0.3 mm. The usable range for the film with 2 barriers was from ~4 to ~40 Jcm-2, while the usable range for the film with 5 barriers was from ~30 to ~300 Jcm-2. Using both EBT3 films covered with 2 and 5 barriers will give a continuous usable range from 4 to 300 Jcm-2, which will be useful for a consecutive 6-d UV exposure measurement.