The isotope ratio or the isotope signature of a chemical element , which is determined by the atomic number, is understood as the relative frequency of the isotopes of this element. The isotopes differ in their neutron number and mass number . In the Wikipedia info box representations, the isotope ratios are given under the abbreviation NH (for natural abundance).
For example, natural uranium has an isotope ratio of 99.3% 238 U to 0.7% 235 U. In order to use uranium as a nuclear fuel , the isotope ratio of 235 U for most types of nuclear reactors must be increased to 3-5% by so-called uranium enrichment become.
Determination and age determination
The isotope ratio can be determined directly via mass spectrometry or, in the case of radioactive isotopes, indirectly via the radiation intensity. One area of application for determining the isotope ratio is age determination . The age of the earth and the solar system can be precisely determined using long-lived radioactive isotopes . The most important methods for this are potassium-argon dating and uranium-lead dating . In archeology , carbon-14 dating plays an important role for organic materials up to an age of 50,000 years.
Determination of origin
The determination of the isotope signature can also be used to determine the origin. For example, different lead deposits differ not only in the proportion of other heavy metals but also in the ratio of 208 Pb to 206 Pb.
The isotope ratios generally given for various elements such as hydrogen , oxygen , carbon and nitrogen are mean values . In fact, however, these show strong regional fluctuations. The origin of plant and animal products can be determined by determining the proportions of the stable isotopes.