Nuclear chemistry transuranium elements

MCMILLAN, EDWIN M. (1907-1991). An American physicist who won the Nobel prize in chemistry in 1951 along with Glenn T. Seaborg lor their discoveries In the chemistry of the transuranium elements. His work included research in nuclear physics and particle accelerator development as well as microwave radar and sonar. He and his colleagues discovered neptunium and plutonium. He was the recipient of the Atoms for Peace prize in 1963. His Ph D. in Physics was awarded from Princeton University. 

The chemical elements are the building blocks of nature. All substances are combinations of these elements. There are (as of 2005) 113 known chemical elements with the heaviest naturally occurring element being uranium (Z = 92). The 22 heaviest chemical elements, the transuranium elements, are manmade. The story of their synthesis, their properties, their impact on chemistry and physics, and their importance to society is fascinating. This story is of particular importance to nuclear chemistry because most of our knowledge of these elements and their properties comes from the work of nuclear chemists, and such work continues to be a major area of nuclear chemical research. One of us (GTS) has been intimately involved in the discovery and characterization of these transuranium elements. 

The redox chemistry of the actinide elements, especially plutonium, is complex (Katz et al., 1980). Disproportionation reactions are especially important for the +4 and +5 oxidation states. Some of the equilibria are kinetically slow and irreversible. All transuranium elements undergo extensive hydrolysis with the +4 cations reacting most readily due to their large charge/radius ratio. Pu (IV) hydrolyzes extensively in acid solution and forms polymers. The polymers are of colloidal dimensions and are a serious problem in nuclear fuel reprocessing. 

In this sense, Lise Meitner had her title right, for the experiments and theories of nuclear physics and chemistry that were used to pursue the false transuranium elements did lead to the recognition of fission, and the scientists who worked most assiduously on the transuranium project were those who did, finally, succeed in making the discovery. 

It is at this point, when the supposed transuranium elements were out of the picture, that the problem was finally solved. It happened because the chemists were now in familiar territory, with elements of known chemistry and tested radiochemistry. When their findings contradicted the physics assumption of small nuclear changes, the discrepancy was apparent and had to be resolved. It can be argued that their interdisciplinary collaboration functioned best just when Meitner was physically separated from her Berlin colleagues, and it is ironic that their separation produced a correspondence that demonstrates how effective this collaboration was. 

LaChapette, T. J., L. B. Magnusson, and J. C. Hindman The Chemistry of Neptunium. First Preparation and Solubilities of some Neptunium Compounds in Aqueous Solution. In G. T. Seaborg, J. J. Katz, and W. M. Manning (Eds.), The Transuranium Elements, National Nuclear Energy Series, Div. IV, Vol. 14B, p. 1097. New York McGraw-Hill 1949. 

Nuclear chemistry describes reactions involving changes in atomic nuclei. In Lesson 2, elements were defined as matter that cannot be broken down by simple means. Some isotopes are radioactive and are broken down by nuclear processes. Radioactivity is the process by which unstable nuclei break down spontaneously, emitting particles and/or electromagnetic radiation (i.e., energy), also called nuclear radiation. Heavy elements (from atomic number 83) are naturally radioactive, and many more (the transuranium elements, atomic numbers 93 to 116) have been generated in laboratories. 

At one time it was considered extremely unlikely that there would be any significant chemistry for elements with atomic numbers greater than about 100. The nuclear stability of the transuranium elements decreases with atomic number, so that the half-lives for the heaviest elements (Table 14.5) become too short for fruitful chemical studies (i.e., /j seconds).6o However, advanced chemical techniques have helped... 

The separation of actinides has been studied for various purposes in Japan Atomic Energy Research Institute (JAERI). The works which have been carried out so far, are classified into four categories preparation studies of actinides nuclides, separation chemistry for chemical analysis, separation of actinides from radioactive waste, and studies on reprocessing of spent nuclear fuels. The present work is to review studies of actinide separation performed in JAERI, emphasizing the need of the separation for the main purpose of individual. Concern is focussed on the separation of transuranium elements and studies on thorium and uranium are put aside. 

Hahn, Otto. (1879-1968). A German physical chemist who won the Nobel Prize for chemistry in 1944 for atom splitting and the principle of the chain reaction. Well-known for work on nuclear fission he discovered protactinium and transuranium elements with atomic numbers 94,95, and 96. After receiving his doctorate at the University of Munich, he worked in Canada before returning to Europe. 

Seaborg went on to the University of California at Berkeley for graduate work, obtaining his Ph.D. in 1937. It was around this time that his interest in transuranium elements (elements of higher atomic number than uranium) took shape. His research interest was in nuclear physics but, as he once said, one could get a chemistry Ph.D. in those days doing nuclear physics. ... 

The use of the actinide elements fall into three categories (i) for imderstanding fundamental chemistry and the nature of the periodic system, (ii) as products, in the large scale use of nuclear energy, and (iii) miscellaneous applications, where the particular physical, chemical or nuclear properties are valuable. Only the last aspect is discussed here, the others are treated elsewhere in this book. The availability of transuranium element isotopes suitable for experiments is listed in Table 16.4. 

We simply define radiochemistry and nuclear chemistry by the content of this book, which is primarily written for chemists. The content contains fimdamental chapters followed by those devoted to applications. Each chapter ends with a section of exercises (with answers) and literature references. An historic introduction (Ch. 1) leads to chapters on stable isotopes and isotope separation, on unstable isotopes and radioactivity, and on radionuclides in nature (Ch. 2-5). Nuclear radiation - emission, absorbance, chemical effects radiation chemistry), detection and uses - is covered in four chapters (Ch. 6-9). This is followed by several chapters on elementary particles, nuclear structure, nuclear reactions and the production of new atoms (radio-nuclides of known elements as well as the transuranium ones) in the laboratory and in cosmos (Ch. 10-17). Before the four final chapters on nuclear energy and its environmental effects (Ch. 19-22), we have inserted a chapter on radiation biology and radiation protection (Ch. 18). Chapter 18 thus ends the fimdam tal part of radiochemistry it is essential to all students who want to use radionuclides in scientific research. By this arrangement, the book is subdivided into 3 parts fundamental ladiochemistry, nuclear reactions, and applied nuclear energy. We hope that this shall satisfy teachers with differrat educational goals. 

Between 1944 and 1958, Seaborg and his coworfcers also identified various products of nuclear reactions as being the elements having atomic numbers 95 through 102. aD these elements are radioactive and are not found in nature they can be synthesized only via nuclear reactions. For their efforts in identifying the elements beyond uranium (the transuranium elements), McMillan and Seaborg shared the 1951 Nobel Prize in Chemistry. 

Abstract This chapter reviews the historical perspective of transuranium elements and the recent progress in the production and study of nuclear properties of transuranium nuclei. Exotic decay properties of heavy nuclei are also introduced. Chemical properties of transuranium elements in aqueous and solid states are summarized based on the actinide concept. For new application of studying transuranium elements, an X-ray absorption fine structure (XAFS) method and computational chemistry are surveyed. 

Experiences with aqueous chemistry and behavior of the transuranium elements obtained in nuclear fuel reprocessing and plutonium processing are only of limited relevance for PWR primary coolants with the extremely low concentrations of these elements in a boric acid—LiOH solution of varying composition. The plutonium polymers which are formed in less acid and neutral solutions and which have been reported to show the highest plate-out potential (e. g. Wilkins and Wisbey,... 

We have already described two applications of nuclear chemistry. One was the preparation of elements not available naturally. We noted that the discovery of the transuranium elements clarified the position of the heavy elements in the periodic table. In the section just completed, we discussed the use of radioactivity in dating objects. We will discuss practical uses of nuclear energy later in the chapter. Here we will look at the applications of radioactive isotopes to chemical analysis and to medicine. 

The discovery and identification of element 101 (mendelevium, Md) was a landmark experiment in many ways [ 1 ]. It was the first new transuranium element to be produced and identified on the basis of one-atom-at-a-time chemistry and it is also the heaviest element (to date) to be chemically identified by direct chemical separation of the element itself. All of the higher Z elements have been first identified by physical/nuclear techniques prior to study of their chemical properties. In fact, one of the criteria for chemical studies is that an isotope with known properties be used for positive identification of the element being studied. Due to relativistic effects [1] chemical properties cannot be reliably predicted and a meaningful study of chemical properties cannot be conducted with both unknown chemistry and unknown, non-specific nuclear decay properties ... 

The fate of actinide elements introduced into the environment is of course not merely a scientific issue. The disposal of the by-products of the nuclear power industry has become a matter of public concern. For each 1000 kg of uranium fuel irradiated in a typical nuclear reactor for a three-year period, about 50 kg of uranium are consumed. In addition to a large amount of energy evolved as heat, 35 kg of radioactive fission products and 15 kg of plutonium and transplutonium elements are produced. Many of the fission-product nuclides are stable, but others are highly radioactive. All of the fission products are isotopes of elements whose chemical properties are well-understood. The transuranium elements produced in the reactor by neutron capture, however, have unique chemical properties, which are reasonably well-understood but are not always easily inferred by extrapolation from the chemistry of the classical elements. Plutonium is fissile and can be recycled as a nuclear fuel in conventional or breeder reactors, but the transplutonium elements are not fissile to the extent of supporting a nuclear chain reaction, and in any event they are produced in amounts too small to be of interest for large-scale uses. The transplutonium elements must therefore be secured and stored. 

Seaborg, Glenn Theodore (1912-99) An American chemist noted as one of the discoverers of plutonium (plutonium-238 and plutonium-239). Gaining his doctorate in 1937 from the University of California, he was appointed professor of chemistry in 1945. He was responsible for nuclear chemical research at the Lawrence Radiation Laboratory and headed the Manhattan Project group from 1942 to 1946 that devised the chemical extraction processes used in the production of plutonium. He codiscovered nine other transuranium elements, including the element seaborgium, atomic number 106, which is named after him. He was awarded the Nobel Prize in Chemistry in 1951. 

In 1934, nuclear physics was young and the neutron had only just been discovered, yet the transuranium project was approached with a remarkable degree of confidence. The concepts from chemistry and nuclear physics that framed and guided the investigation were never seriously questioned, even though the synthesis and identification of new elements was, by definition, a leap into the unknown. Similarly, researchers were relatively unconcerned about the limitations of their small-scale experiments, even though the experiments themselves were notoriously difficult due to the tiny quantities of radioactive material. 

---