Nuclear proliferation Alliance of Nuclear Weapons and Nuclear Power", tritium is not classified as a "special nuclear material" but rather as a by-product. It is seen as an important litmus test on the seriousness of the United States' intention to nuclear disarm. This radioactive super-heavy hydrogen isotope is used to boost the efficiency of fissile materials in nuclear weapons. The United States resumed tritium production in 2003 for the first time in 15 years. This could indicate that there is a potential nuclear arm stockpile replacement since the isotope naturally decays. In May 1995, NPT parties reaffirmed their commitment to a Fissile
Isotope persisted down to the present because their rate of decay is so slow (e.g. uranium-238 and potassium-40). Post-primordial isotopes were created by cosmic ray bombardment as cosmogenic nuclides (e.g., tritium, carbon-14), or by the decay of a radioactive primordial isotope to a radioactive radiogenic nuclide daughter (e.g. uranium to radium). A few isotopes are naturally synthesized as nucleogenic nuclides, by some other natural nuclear reaction, such as when neutrons from natural nuclear fission are absorbed by another atom. As discussed above, only 80 elements have any stable isotopes, and 26 of these have only one stable isotope. Thus, about two-thirds