Perturbed angular correlations in relation to chemical analysis

For a profound insight into the role of essential and toxic elements, it is important to know the nature and the properties of the chemical forms in which the elements exist. The chemical and physical status of atoms has virtually no or only limited effect on the nuclear decay parameters, and the eventual effects are often small and hard to measure. Still, techniques have been developed in which use is made of nuclear properties sensitive to the chemical status of a radioactive nuclide and the chemical properties of its environment. Examples are Mossbauer spectroscopy, nuclear magnetic resonance spectroscopy, positron annihilation spectroscopy, and the measurement of perturbed angular correlations (PACs). Although most applications of PAC are reported in solid-state chemistry, the technique has also been recognized as highly valuable in studies of macromolecules and biomolecules. For these fields of application, the technique offers the possibilities of in situ and in vivo measurement, experiments in easily disturbed equilibrium systems, and use of low concentrations of the nuclide of interest. In this paper, prospects and limitations of the PAC method used at the Interfaculty Reactor Institute are discussed using examples of applications in biological systems