Radiochemistry

Assistant Lecture
Najlaa Nassir
Radiochemistry:-
Is the branch of chemistry concerned with the chemistry of radioisotopes, elements, and substances, the laws governing the physicochemical behavior of this radioactive matter, the chemistry of nuclear transformations, and the physicochemical processes that accompany these transformations, because of the topics, methods, and objects of its investigations, can be subdivided into general radio-chemistry, the chemistry of nuclear transformations, the chemistry of radioactive elements, and applied radiochemistry.
General radiochemistry studies the physicochemical regularities in the behavior of radioisotopes and elements. Radioisotopes, which differ little in their chemical properties from nonradioactive isotopes, are present, though in extremely low concentrations, in ores and other natural substances, in products obtained synthetically, and in the solutions formed after processing raw materials. The decay these isotopes undergo is accompanied by nuclear radiation. Most natural radioisotopes are daughter isotopes, that is, products of the decay of 238U,
Radioisotopes are also obtained artificially by irradiating various substances with nuclear particles. The yield is of the order of 10–8–10–12 percent by weight. In many cases, hundreds, tens, or even just a few atoms of radioisotopes are present in many other atoms. (Only in the production of nuclear fuel is Pu obtained in significant quantities, though even here its concentration upon irradiation of U with neutrons is low.) It is therefore possible to separate radioactive elements and isotopes only from extremely dilute systems, and their weights in most cases cannot be determined. The physicochemical behavior of extremely dilute solutions is very complex. This behavior may be described by the laws of ideal solutions, though sometimes these laws are not obeyed because of secondary processes related to, for example, adsorption or radiolysis. General radio-chemistry includes the study of isotopic exchange, processes involving the distribution of trace amounts of radioisotopes between phases, processes of coprecipitation, adsorption, and extraction, the electrochemistry of radioactive elements, and the state of radioisotopes in extremely dilute systems—the dis-persity of the elements (formation of radio colloids) and the formation of complexes . The chemistry of nuclear transformations includes the study of the reactions of atoms formed in nuclear transformations (hot atoms), the products of nuclear reactions, and the methods for obtaining, concentrating, and separating radioisotopes and their nuclear isomers. Also studied are the properties of radioactive substances and the transformations of these substances under the effect of their own radiation.
The chemistry of radioactive elements is the chemistry of the natural radioactive elements from Po to U (atomic numbers 84–92) and of the artificial elements Tc (atomic number 43), Pm (atomic number 61), Np (atomic number 94), and all subsequent elements up to atomic number 106. By convention, the chemistry and technology of nuclear fuel is included in this subdivision. Nuclear fuel entails the production and chemical separation of 239Pu from irradiated uranium, of 233U from thorium irradiated with neutrons, and of 235U from a natural mixture of isotopes.
Applied radiochemistry is concerned with the development of methods for the synthesis of labeled compounds, the use of radioisotopes in chemistry and the chemical industry, and the use of nuclear radiation in chemical analysis, for example, in nuclear gamma-ray fluorescence spectroscopy.
The objects of radiochemical investigations are radioactive substances containing radioisotopes, many of which are characterized by a short lifetime and nuclear (radioactive) radiation, which necessitates the use of special methods of investigation.
Radioactive emissions permit the use of special radiometric methods in radiochemistry for measuring the quantity of a radioactive substance. These emissions, however, necessitate the use of special safety techniques because emissions in doses exceeding certain levels are harmful to human health. Since the methods for measuring radioactivity are of superior sensitivity, work can be done with a minimal amount of material, an amount that would not lend itself to study under any other methods. Using instruments common in radiochemical laboratories, it is possible to detect, for example, 10–10—10–15 gram of 226Ra, 10–17 gram of 32P, or 10–17 gram of 222Rn. By using especially sensitive methods for monitoring radioactive decay, it is possible to detect the presence of single atoms of a radioisotope and to establish the fact of their decay.
The development of radiochemistry into an independent branch of chemistry began at the end of the 19th century with the work of M. Sk?odowska-Curie and P. Curie, who in 1898 discovered and isolated Ra and Po. Sk?odowska-Curie was the first to use the methods of coprecipitation of trace amounts of radioactive elements from solution with large amounts of analogous elements. In 1911, F. Soddy defined radiochemistry as the science concerned with the study of the properties of the products of radioactive transformations and with the separation and identification of these products. Four periods can be discerned in the development of radiochemistry, each of which is related to progress in the study of radioactivity and nuclear physics.