For shielding calculations, dispersion calculations or to determine local dose rates, it is often sufficient to consider only a few special radionuclides, the leader nuclides. The latter have a chemical similarity and/or such a high specific decay energy that they override the effects of lower radiating radionuclides. The fact that they are disregarded in calculation therefore does not entail an error in the radiation protection calculations. Reference nuclides are also used to calculate the quantity of other nuclides in the case of known history of the material containing the nuclide(s).