99Tc in the environment. Sources, distribution and methods

99Tc is a β-emitter, Emax=294 keV, with a very long half-life (T1/2=2.11 x 105 y). It is mainly produced in the fission of 235U and 239Pu at a rate of about 6%. This rate together with its long half-life makes it a significant nuclide in the whole nuclear fuel cycle, from which it can be introduced into the environment at different rates depending on the cycle step. A gross estimation shows that adding all the possible sources, at least 2000 TBq had been released into the environment up to 2000 and that up to the middle of the nineties of the last century some 64000 TBq had been produced worldwide. Nuclear explosions have liberated some 160 TBq into the environment. In this work, environmental distribution of 99Tc as well as the methods for its determination will be discussed. Emphasis is put on the environmental relevance of 99Tc, mainly with regard to the future committed radiation dose received by the population and to the problem of nuclear waste management. Its determination at environmental levels is a challenging task. For that, special mention is made about the mass spectrometric methods for its measurement. (author)