Radiochemical and isotopic analysis methods

Radiochemical and isotopic analysis methods are many and varied. What they have in common is that the measurements concern the properties of the atom's nucleus, rather than its electron chain. In this way, the chemical bond is eliminated. These measurements are highly sensitive and selective, whether they concern the radiation emitted by radioactive isotopes or the mass of stable isotopes. Radiochemical and isotopic analysis methods are most often used to determine very small quantities of matter in the microgram to picogram fraction range. They can be applied to the determination of most elements. They are often multi-elemental, simple and quick to use. They can be highly effective in speciation studies.

We have classified these methods into three groups:

• those that use the measurement of pre-existing isotopes in the medium to be characterized;

• those involving the addition of a stable or radioactive isotope to the medium to be characterized;

• those that use irradiation of the medium to be characterized to generate either radiation measured during irradiation, or radioactive isotopes measured after irradiation has ended.

Radiochemical and nuclear analysis methods reached their peak in 1960-1970, with the spread of irradiation facilities worldwide (nuclear reactors, particle gas pedals, isotopic sources) and the advent of high-performance measurement electronics (semiconductor detectors and microcomputers), enabling the development and automation of analyses without chemical treatment. Since then, other high-performance methods based on different excitation and detection principles have been developed and/or introduced (excitation by plasma, laser, cyclotron radiation, etc., gas pedal mass spectrometry measurements, time-resolved fluorescence, photoacoustic spectroscopy, etc.). These methods can achieve equivalent detection sensitivities and provide complementary information. Above all, they have the advantage of not using radioactive elements, thus avoiding the growing constraints generated by their use. Radiochemical and nuclear methods retain their raison d'être, as they are often simpler and easier to implement. In many cases, the equipment used is less expensive, and the results obtained less prone to error. It should be remembered that the radioactivity to be handled is low and perfectly controlled. Over the last ten years, the Chernobyl accident and the problem posed by the disposal of nuclear waste have rekindled research in the field of radiochemistry, which goes well beyond the scope of this paper [1]. This article will not deal with isotopic labeling outside its use in quantitative elemental analysis, nor with the use of radioelements...