Isotopes of hydrogen used for deuterium and tritium. The IUPAC accepts the D and T symbols, but recommends instead using standard isotopic symbols (H and H) to avoid confusion in the alphabetic sorting of chemical formulas. The ordinary isotope of hydrogen, with no neutrons, is sometimes called "protium". (During the early study of radioactivity, some other heavy radioactive isotopes were given names, H (atomic mass u) is the most common hydrogen isotope with an abundance of more than 99.98%. Because the nucleus of this isotope consists of only a single proton, it is given the formal name "protium". The proton has never been
Tritium radioluminescence not noticeable in bright conditions such as during daylight, however. As a result, some manufacturers have started to integrate fiber optic sights with tritium vials to provide bright, high-contrast firearms sights in both bright and dim conditions. While these devices contain a radioactive substance, it is currently believed that self-powered lighting does not pose a significant health concern. A 2007 report by the UK government's Health Protection Agency Advisory Group on Ionizing Radiation declared the health risks of tritium exposure to be double than previously set by the International Commission on Radiological Protection, but encapsulated tritium lighting devices, typically taking