Radioelement

Alpha counting is done with an internal proportional counter or a scintiUation counter. Beta counting is carried out with an internal or external proportional gas-flow chamber or an end-window Geiger-MueUer tube. The operating principles and descriptions of various counting instmments are available, as are techniques for determining various radioelements in aqueous solution (20,44). A laboratory manual of radiochemical procedures has been compiled for analysis of specific radionucHdes in drinking water (45). Detector efficiency should be deterrnined with commercially available sources of known activity. 

Research into the aquatic chemistry of plutonium has produced information showing how this radioelement is mobilized and transported in the environment. Field studies revealed that the sorption of plutonium onto sediments is an equilibrium process which influences the concentration in natural waters. This equilibrium process is modified by the oxidation state of the soluble plutonium and by the presence of dissolved organic carbon (DOC). Higher concentrations of fallout plutonium in natural waters are associated with higher DOC. Laboratory experiments confirm the correlation. In waters low in DOC oxidized plutonium, Pu(V), is the dominant oxidation state while reduced plutonium, Pu(III+IV), is more prevalent where high concentrations of DOC exist. Laboratory and field experiments have provided some information on the possible chemical processes which lead to changes in the oxidation state of plutonium and to its complexation by natural ligands. 

Wollenberg, H.A., Naturally Occurring Radioelements and Terrestrial Gamma-ray Exposure Rates An Assessment Based on Recent Geochemical Data, Report LBL-18714, Lawrence Berkeley Laboratory, Berkeley CA (1984). 

The ionization of nitrogen, oxygen and trace gas molecules in the air due to the presence of the natural radioelements in the soil and air and the cosmic radiation has a direct effect upon the electrical characteristics of the atmosphere. 

Radiocerium can also gain entry into food crops through irrigation or flooding of fields with waters containing these nuclides. However, only small amounts of radiocerium enter food crops by this route compared to the more soluble radioelements that have been studied. Cerium-144 originating from both the Hanford reactors and worldwide... 

Golchert NW, Iwami FS, Sedlet J. 1980. Determination of actinides in soil. In Lyon WS, ed. Radioelement analysis progress and problems. 23rd conference Analytical Chemistry in Energy Technology, Gatlinburg, TN, Oct 9-11, 1979. Ann Arbor, Ml Ann Arbor Science Publishers, Inc., 215-222. 

Tadmor J. 1986. Atmospheric release of volatilized species of radioelements from coal fired plants. Health Phys 50 270-273. 

See also Fajans, K. Radioelements and Isotopes. Chemical Forces and Optical Properties of Substances, p. 86. New York McGraw-Hill Book Co 1931. 2 Hughes, H. K. Phys. Rev. 72, 614 (1947). 

Actinides, the chemical elements with atomic numbers ranging from 89 to 103, form the heaviest complete series in the Periodic Table. They are radioelements, either naturally occurring or synthesized by nuclear reactions. Their predominant practical application depends on the nuclear properties of their isotopes decay, spontaneous or induced fission. Their chemical and physical properties reflect a very complex electronic structure, and their study and understanding are a challenge to experimentalists and theoreticians. 

To remove radium and other radioactive constituents from pitchblende, Hahn and Meitner treated pulverized pitchblende repeatedly and for long periods of time with hot concentrated nitric acid. From the insoluble siliceous residue they separated a new radioactive substance, which they called protoactinium. This name has subsequently been shortened to protactinium. When they added a little tantalum salt to a solution containing protactinium, the reactions of the new substance so closely resembled those of tantalum that Hahn and Meitner were unable to separate the two substances (118). Since tantalum is not radioactive, the protactinium could thus be obtained free from other radioelements. Since protactinium is not an isotope of tantalum, it should be possible to separate them from each other (119). By working up large quantities of rich pitchblende residues from the Quinine Works at Braunschweig, Hahn and Meitner were able to extract more active preparations of the new element (49). 

Jean-Fr6ddric Joliot, 1900-1958. Physicist and chemist at the Curie Institute. He has made many important researches on the phenomenon of recoil and the conservation of momentum, on the electrochemical behavior of the radioelements, and on the expulsion of atomic nuclei and the existence of the neutron. 

Fig- 2. Radioelement concentrations in solutions contacted with powdered spent fuel (UO2 bum-up 50 MW d/kg U -y-dose rate 10 Mrad/h solid surface/solution volume ratio 1000/m at 25 °C) after sequential filtration (filter pore size 450 nm - white bars filter pore size 1.8 nm -> grey bars) solutions consist of concentrated brine (5 mol/kg NaCl) and simulated granitic groundwater (I = 2.8 x 10 1 mol/L, pH 8) (Geckeis et at. 1998). 

Fig. 3, Evolution of Am(HI), Eu(III) and U concentrations with time in spent fuel pellet leaching experiments (leachate 5 mol/kg NaCl solution anaerobic conditions) radionuclides found in ultrafiltered samples (uf filter pore size 1.8 nm) arc considered as truly dissolved radionuclide concentrations found in filtered samples (f filter pore size 450 nm) are attributed to truly dissolved + colloidal species the grey shaded area marks the fraction of colloidal radioelement species in solution the black arrow indicates the pH increase in solution during the leaching experiment (Geckeis et al. 1998).

Bagnall, K. W., Chemistry of the Rare Radioelements. Butterworths, London, 1957. 

Dupuis, M., "Distribution and Evolution of Radioelements After a Nuclear Explosion," UCRL-Trans-10617-5, Lawrence Livermore Laboratory, (1972), from Bull. Infor. Sci. Tech., 149, 41 (1970). 

In this equation, the term in parentheses is called the saturation factor. This factor tends rapidly to 1 when t is increased. Thus, for t = 6r, the activity reaches a value of 98%. Experimentally, the time of irradiation never exceeds 4 to 5t. This method is usually reserved for radioelements with short half-lives. 

For certain samples, the radioelement under analysis can be isolated using its stable isotope and a training technique. A similar treatment carried out on the reference sample allows the extraction yield to be determined. The result is then normalised to 100%. 

Although care must always be exercised to avoid undue exposure to various radioisotopes, these materials have found wide acceptance in analytical chemistry, medicine, radiocarbon and other radioelement dating (geology, archaeology, etc.), and other special situations—for example, as a fuel source in spacecraft. 

Radiochemistry is defined as the chemical study of radioactive elements, both natural and artificial, and their use in the study of chemical processes (Random House Dictionary, 1984). Operationally, radiochemistry is defined by the activities of radiochemists, that is, (a) nuclear analytical methods, (b) the application of radionuclides in areas outside of chemistry, such as medicine, (c) the physics and chemistry of the radioelements, (d) the physics and chemistry of high-activity-level matter, and (e) radiotracer studies. We have dealt with several of these topics in Chapters 4, 13, 15, and 16. In this chapter, we will discuss the basic principles behind radiochemical techniques and some details of their application. 

The chemical components with the most effect on radioelement solubility and sorption were NaOH, NaA102, EDTA, and HEDTA. The EDTA and HEDTA increased Co, Sr, and Am solubility and decreased sorption for almost all radioelements studied. Sodium hydroxide and NaA102 increased Pu solubility and decreased Np and Pu sorption. Sodium nitrite decreased Np solubility, while Na2C03 and HEDTA increased it. These observations give evidence for the formation of radioelement complexes which are soluble and are not strongly sorbed by the sediments near the waste tanks. 

High-level defense waste solutions resulting from plutonium recovery and waste processing activities currently are stored in mild steel-lined concrete tanks located underground at the U.S. Department of Energy s Hanford Site. Low radioelement solubility and extensive radioelement sorption on surrounding sediment help maintain isolation of hazardous radionuclides from the biosphere in the event of tank failure. 

Chemical components in the waste solutions potentially could affect radioelement solubility and sorption reactions, and thus enhance or reduce radionuclide transport. The effects of 12 chemical components on the solubility and sorption of cobalt, strontium, neptunium, plutonium, and americium were studied to... 

The 12 waste components were selected for study based on their quantities in the Hanford HLW solutions and their abilities to complex, or influence the complexation of metallic radioelements. The range of chemical component concentrations studied, given in Table I, was broadly representative of concentrations found in HLW. 

Five radioelements were selected for study cobalt,... 

Each sorption experiment was conducted by adding 5.0 mL of the appropriate traced solution, prepared as described above, to a weighed (-1 g) portion of Hanford sediment. To simulate advancement of a radioelement plume from a failed tank through previously waste-wetted sediment, each sediment sample was preequilibrated twice with the relevant untraced solution prior to introduction of the traced solution. Each pre-equilibration lasted at least 2 hr. Following a 7-day equilibration with the traced solution, each sediment-solution mixture was centrifuged, the solution was filtered through an ultrafilter, and the radionuclide solution concentration was determined. Distribution coefficients and fractions of radionuclides sorbed were determined for each sorption experiment. The distribution coefficient, Kd, is the activity per gram of sediment divided by the activity per mL of solution at equilibrium. 

Radioelement NaN03 NaN02 NaOH NaA102 Na2C03 Na2S04 Na3P04 NaF HEDTA EDTA Sodium hydroxy -acetate Sodium citrate... 

The oxidation-reduction behaviors of neptunium, plutonium and americium in basic solution have been determined via polarographic and coulometric studies (6-9). These studies, which showed that the more soluble (V), (VI), and (VII) oxidation states of these actinides are stable in alkaline solution under certain redox conditions, helped identify possible actinide species and oxidation states in our experiments. Actual identification of radioelement oxidation states was not done in the present experiments. 

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