What is concerned by Radiochemistry ?
Since more than forty years, one call Radiochemistry, essentially, as proposed by Irene Joliot-Curie, the researches dealing with Chemistry of Radioelements.
The considered elements are primarily the fifteen actinides (5f elements). They are often studied in comparison with lanthanides (4f elements) for which one has γ emitter radioisotopes. These 30 elements represent the heart of the scientific domain. They are the center of the Conferences dedicated to Radiochemistry.
However, recently, radiochemical researches have included new elements:
- Transactinide elements have been synthesized and, with discovery of isotopes with half lives larger than one second, physico-chemical studies have been carried out,
- Then, in the frame of applied researches related with treatment and storage of nuclear wastes, radiochemists have now to study fission product isotopes with long half lives. It is mainly, technetium, selenium, zirconium, palladium, tin, iodine and cesium.
Considering also radioactive elements such as polonium, francium, radium and astatine, we have to conclude that Radiochemistry covers a large part of the Inorganic Chemistry. About 40% of the elements from the Periodic Table are concerned.
As for any scientific researches, it is also necessary to consider the society needs, and technologic or industrial applications. The most important applications leading to a variety of new and interesting researches are nuclear energy, environment, and with less strong connections, geology, nuclear medicine, archaeology... There are also "radiochemical" methods, where radiation measurements allow considering applications in a large variety of fields.
What are the basic researches to carry out in this part of the Periodic Table ?
We can, as usual with Inorganic Chemistry, consider Solid Chemistry with investigations of metals and important compounds. But, in Radiochemistry, the available materials are limited in comparison with natural and non radioactive elements. This is due to the lack of materials for heavy elements, the radioactivity of the compounds which could induce crystallographic damages, the impossibility to synthesize several elements in large weighable amounts, the difficulty to handle radioactive materials and the restricted number of laboratory able to perform such difficult studies. However, property of metals and acquisition of crystallographic and physic data of simple compounds are, of course, extremely important to get information on chemical bonds, properties of the 5f orbital and interatomic distances which are of constant need in physical chemistry.
The unique possibility to perform radiochemical experiments at the tracer scale or even atom by atom scale, give an exceptional opportunity to consider, for all elements, solution chemistry and to develop theoretical chemistry especially to evaluate properties which are difficult to be directly measured. Moreover, appearance of exotic and significant phenomena such as "relativistic effects", make this theoretical approach particularly useful.
The most fundamental researches to consider are, to our point of view:
- The evaluation of ionic radii and interatomic distances, considering ions in solution: for that purpose, after reliable crystallographic determinations, the ionic local structure of ions in solutions are needed (cation-ligand distance measurements, coordination chemistry and EXAFS experiments),
- The knowledge of the stability of the possible oxidation states and determinations of redox potentials for the considered MX/MY couple,
- The determinations of the thermodynamic properties of species,
- Comparative studies between 4f and 5f elements, between transactinides, actinides and d elements,
- The theoretical investigations to interpret the experimental observations and to allow modelling, evaluations and predictions of unknown characteristics.
In the case of the 5f series, it appears that, at least, five remarkable properties are to be considered and discussed:
- The existence of a large number of oxidation states for a majority of the elements,
- The progressive change of the size of the ions in solution,
- The change of the chemical bond from covalent to ionic,
- The progressive change of the coordination number when atomic number is increasing,
- The appearance of relativistic effect at the end of the Periodic Table.
For these reasons the chemistry of these radioactive elements (and consequently Radiochemistry) is particularly interesting and important to study before considering separation chemistry to be used, for instance, in the treatment of radioactive wastes.
In our researches, we have chosen to examine successively, most of these properties and we will propose some illustrative data and figures, with related publications in the different fields. We will also consider different applications of radiochemical studies in the nuclear energy.
Finally, we have included several documents, reports for a prospective in Radiochemistry, historical paper of the French - Russian radiochemical cooperation and others.
This site will be extended. We would like to emphasize that some reported data and figures in chapter 1.4. and 1.6. are working documents and will be completed and corrected in the future.
We hope that these documents will promote comments and discussions.