Tracer scale

P0O3 may have been detected on a tracer scale but has not been characterized with weighable amounts of the element. 

Although the outline of a chemical separation process could be obtained by tracer-scale investigations, the process could not be defined with certainty until study of it was possible at the actual separation plants. Therefore, the question in the summer of 1942, was as follows How could any separations process be tested at the concentration of plutonium that would exist several years later in the production plants when, at this time, there was not even a microgram of plutonium available This problem was solved through an unprecedented series of experiments encompassing two major objectives. First, it was decided to attempt the production... 

Unfortunately, when elements are very hydrolyzable colloidal forms can occur on a tracer scale in the absence of complexing ions such hydrolysis causes the resulting experimental data to be questionable. 

All the early work on plutonium was done with unweighable amounts on a tracer scale. When it became apparent that large amounts would be needed for the atomic bomb, it was necessary to have a more detailed knowledge of the chemical properties of this element. Intensive bombardment of hundreds of pounds of uranium was therefore begun in the cyclotrons at Berkeley and at Washington University in St. Louis. Sepa-ration of plutonium from neptunium was based on the fact that neptunium is oxidized by bromate while plutonium is not, and that reduced fluorides of the two metals are carried down by precipitation of rare earth fluorides, while the fluorides of the oxidized states of the two elements are not. Therefore a separation results by repeated bromate oxidations and precipitations with rare earth fluorides. 

There is tracer scale evidence455 for the formation of the Cf02 ion during ozonization of 249Bk and subsequent jS decay to 249Cf. However, the only compounds isolated in this oxidation state are all americium(V) species. 

Protactinium-233 and neptunium-239 diphthalocyanines are prepared from the corresponding thorium-232 and uranium-238 diphthalocyanines by element transformation [6]. The existence of Pa and Np di-Pcs is proven by repeated sublimation of the irradiated parent compounds using platinum gauze to retain the impurities. Neptunium di-Pc is also synthesized on the tracer scale from irradiated uranium metal, using the normal synthetic method for uranium di-Pc (Example 29) [6], Other actinide phthalocyanines are reported [107-114], Their structures, as well as those of 200 metal phthalocyanines and their derivatives, are classified in an excellent recent review [115]. More recent experimental data on actinide phthalocyanines are absent in the available literature. 

The question is whether the concepts of thermodynamics and kinetics used in classical chemistry are relevant at tracer scale, ultra-traces and for a single atom ... 

The tracer scale covers usually element concentrations ranging from 10 10 to 10 16 M [2], At such low concentrations, the number of entities present in... 

Thus, because the mass action law applies, the behavior of the microcomponent is expected to be the same at normal concentration and at the tracer scale. In ultra diluted systems, the thermodynamical behavior of an element does not depend on concentrations. However, some discrepancies can occur in particular cases, for example as a result of the different degrees of consumption of ligands leading to unusual complexation reactions or in unexpected redox processes [4], Tracer scale chemistry is also characterized by a kinetics hindrance for reactions between two microcomponents in a given system this trend excludes polymerization reactions or... 

Prior to experiments with SHE, systematic studies with homologues at the tracer scale have to be carried out to select the experimental conditions (solvent extraction, ion exchanger, aqueous media,. ..). On line experiments with short lived isotopes of homologues are also necessary to improve the setup, e.g. to evaluate the eventual impact of edge effects (sorption,. ..). Furthermore, on line experiments involving SHE may preferably be performed with homologues since it is the only way to ensure strictly identical experimental conditions for all present elements. 

Experimentally, limitations are mainly imposed by the one-atom-at-a-time concept since the time devoted to the collection of data may be important. The collection of experimental data must also include effects of the media and the temperature (if used). Prior to experiments to be carried out at the level of a single atom, the absence of edge effects must be checked carefully at the tracer scale. 

Both production of and demand for transplutonium elements are relatively stable, and pressurized ion exchange processes that have been used for several years are entirely satisfactory for these requirements. Three general areas can be visualized which could require extension of these methods. These are (a) tracer-scale separations in the shortest possible time for very shortlived isotopes in nuclear research (b) separations similar to those utilized now, but on a much larger scale, perhaps because of radioactive waste processing or production of heat sources ... 

The isotope 242Cm was first isolated among the products of a-bombardment of 239Pu, and its discovery actually preceded that of americium. Isotopes of other elements were first identified in products from the first hydrogen bomb explosion (1952) or in cyclotron bombardments. Although Cm, Bk, and Cf have been obtained in macro amounts (Table 20-2), much of the chemical information has been obtained on the tracer scale. For the later elements, i.e., those with Z > 100, identification of a few atoms of short lifetime has required the use of very rapid separation techniques and detection based on their nuclear properties. 

By analogy with the other members of the chalcogen family, the compound H2P0 should be expected to exist. Such a compound has never been isolated in weighable quantities and only tracer-scale evidence has been ftimished for its existence. Because of the increasing metalhc nature of the elements as one proceeds to the heavier members of a family, such a compound would predictably be extremely unstable. Hydrogen telluride, for example, is itself unstable with respect to its component elements. 

R. Guillaumont, J. P. Adloff, A. Peneloux, Kinetic and Thermodynamic Aspects of Tracer Scale and Single Atom Chemistry, Radiochim. Acta 46, 169 (1989)... 

Tracer-scale amounts of representative tri-, penta-, and hexavalent / elements were deposited on borosilicate glass surfaces to demonstrate the immobilization of small amounts of heavy-metal cations by phosphate anions. Solid samples containing 1.5 x 10 cpm (1.0 X lO mol), (3.1 x 10 mol), or (4.7 x 10 ... 

We have shown that phytic acid readily hydrolyzes to produce phosphate with a projected lifetime of 100-150 years in the absence of microbiological effects, that actinide-phytate compounds are insoluble, and that europium and uranyl phytates are converted to phosphates within a month at 85 °C. Thorium solubility, on the other hand, is controlled by hydroxide or oxide species. Furthermore, the solubilities of radiotracer europium and uranyl are reduced by phosphate dosing of a simulated groundwater solution, even in the presence of citric acid. In the same systems, neptunium(V) solubility is only affected by 0.01 M phosphate at pH greater than 7. The results of these tracer-scale immobilization experiments indicate that phosphate mineral formation from representative deposits is under thermodynamic control. 

Since 1958, more than 20 nuclides of actinides ranging from neptunium to einsteinium were identified and prepared for tracer studies. From neutron-irradiated uranium samples 2 9Np was adjusted to the pentavalent state and separated by TBP extraction from perchloric acid media. Plutonium-239 was separated by TBP extraction from nitric acid solution followed by anion exchange in a system of Dowex-1 resin and nitric acid. Neptunium-237 was separated from a spent fuel solution of JRR-1 (Japan Research Reactor -1) using anion exchange and TBP extraction. The TBP extraction in the hydrochloric acid medium is a simple and effective technique to purify neptunium from plutonium contamination. On the other hand, both anion exchange and solvent extraction with HDEHP could be used to separate tracer scale plutonium from irradiated neptunium targets. 

Excluded here are those techniques relating to tracer-level work (below weighable quantity of sample measurement by radioassay only), for the concern here will be with the determination of bulk properties of these elements. Tracer-scale studies usually reveal directly only one property of the element under investigation, that is, its relative preference for one environment over another, or more simply, its phase distribution. Nevertheless, as each new transuranium element was discovered and was available only in trace quantities, a great deal of chemistry was learned by inference from tracer-scale studies, including the identity of oxidation states, approximate values of oxidation or reduction potentials, the composition and stability of complex ions, and relative volatilities. 

Guillaumont, R., Adloff, J.-P., and Peneloux, A. 1989. Kinetic and thermodynamic aspect of tracer-scale and single atom chemistry. Radiochim Acta 46, 169-176. 

Beyond einsteinium, the amount of chemical information becomes increasingly sparse but significant dataware obtained in exploratory studies at the tracer scale (see, e.g., Silva 1986) for elements up to the last actinide element, lawrencium (103), and the first transactinide elements, rutherfordium (104) and dubnium (105). From curium on, the chemical properties... 

Guillaumont et al. (1989, 1991), in view of this dilemma, have pointed out that chemical speciation of nuclides at the tracer scale is usually feasible with partition methods in which the... 

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