Isotope fractionation

As isotope is defined as the shift of the frequency of the isotopes of an element caused by physical / chemical processes. Fractionation is thermodynamically and thus temperature dependent.

Overview

The fractionation factor (alpha ) is calculated by the ratio of the isotopes of two samples Rx and Ry.

There are more values ​​that can be used as a measure of the equilibrium degree: separation or isotopic difference () of the enrichment factor (E), and the value. All of these values ​​indicate the ratio of isotopic concentrations. For small deviations from the reference all the values ​​may be used. However, the separation and the enrichment factor are approximations, i.e. for large deviations from the reference should be the other values ​​are used.

Differences are mass-dependent and mass-independent isotope fractionation.

In the mass-dependent isotope fractionation is the change of the frequency ratio of two isotopes of the same element -dependent ( to a first approximation linearly ) from the mass difference of the isotopes. This is the case, for example, in processes such as the kinematic diffusion. Such as lighter isotopes diffuses faster through the porous membrane of a given volume out to be heavier isotopes of the same element. In a three- isotope diagram are samples which have undergone a common origin, but different degrees of mass-dependent isotope fractionation on a Fraktionierungslinie.

In the rarer isotope fractionation massenunabängigen the frequency of one or more isotopes of an element independent of the mass relative to the other isotopes can be changed. Mass -independent isotope fractionation occurs in the upper atmosphere at some photochemical processes. So have demonstrated in ozone formation MH Thiemens and Heidenreich mass-independent isotope fractionation IE.

Applications

Technically significant isotope fractionation, for example, at the uranium enrichment. The study of the isotopic fractionation also plays a role in forensics, such as in the investigation of the origin and purity of food ingredients or the doping control in sport.

The detection of isotope fractionation is also used in the environmental analysis of the origin ( polluter search) and the degradation processes ( Natural Attenuation) in contaminated groundwater. In the geosciences, the Si isotope fractionation continues to be used as a tool for the reconstruction of biogeochemical cycles in the Earth's history. This method belongs to the so-called " non-traditional " stable isotope systems ( Mg, Ca, Si, Ti, Cr, Fe, Cu, Zn, Mo, Tl).

Isotope studies such as Δ18O or Δ13C among the most important method of paleoclimatology. These transmitters can be, for example, Average temperatures reconstruct, but also demonstrate that took place, extensive carbon- entries in the environment that were organic in origin.