Tracer actinide

Figure 3. Percentage of actinide tracers electrodeposited in mercury as a function of time and passed charge. Current density used in this experiment was...

The later chemical work of Silva et was done with the Berkeley 65 s, 261 isotope, and this longer half-life enabled a rapid cation-exchange operation to be undertaken. The material was loaded on to Dowex 50 resin and eluted with ammonium a-hydroxyisobutyrate. Despite complications caused by the daughter No having a very similar alpha spectrum to Rf, it was concluded that Rf eluted in much the same fraction as Hf and Zr tracers, in contrast to actinide tracers which were not eluted in these conditions. 

Tracer studies using 253Es show that einsteinium has chemical properties typical of a heavy trivalent, actinide element. 

Isotopes sufficiently long-Hved for work in weighable amounts are obtainable, at least in principle, for all of the actinide elements through fermium (100) these isotopes with their half-Hves are Hsted in Table 2 (4). Not all of these are available as individual isotopes. It appears that it will always be necessary to study the elements above fermium by means of the tracer technique (except for some very special experiments) because only isotopes with short half-Hves are known. 

Special techniques for experimentation with the actinide elements other than Th and U have been devised because of the potential health ha2ard to the experimenter and the small amounts available (15). In addition, iavestigations are frequently carried out with the substance present ia very low coaceatratioa as a radioactive tracer. Such procedures coatiaue to be used to some exteat with the heaviest actinide elements, where only a few score atoms may be available they were used ia the earHest work for all the transuranium elements. Tracer studies offer a method for obtaining knowledge of oxidation states, formation of complex ions, and the solubiHty of various compounds. These techniques are not appHcable to crystallography, metallurgy, and spectroscopic studies. 

Electrodeposition of Pa metal has been performed from both aqueous and nonaqueous solutions. An isopropanol solution of 10-20 p,gmL Pa from 8M HCl/0.01 M HE/Pa stock was employed for quantitative electrodeposition [41]. The cell consisted of a gold-plated A1 cathode and a Pt wire anode. During deposition the current was maintained at 1 mA, which produced a potential of 400-600 V during the 90-min electrolysis. The progress of the electrolysis was externally monitored by alpha-counting of the electrolysis solution before and during the electrodeposition. Deposition studies of metal from aqueous solutions are more common. Pa was electrodeposited on platinum in 95% yield at tracer concentrations from an electrolyte of [NH4]C1/HC1 [42]. Electrochemical and chemical conditions of the plating process were described for Pu solutions, which served as a model for the other actinide elements studied. Another tracer... 

Under given conditions, colloids do not have an impact on the migration of Sr(II), U(VI) and Np(V), which display only weak or no interaction with the colloids. While Sr(II) migrates as a weak sorbing tracer, the oxidized actinides U(VI) and Np(V) are partly eluted together with the conservative tracer, that is, without retardation. A second part of U(VI) and Np(V) appears slightly retarded probably due to the weak reversible interaction with surfaces of the fracture infill. 

Studied through the use of tracer quantities, the chemical properties of californium indicate that its chemical properties are analogous to those of the tripositive actinides and lanthanides, showing the fluoride and the oxalate to be insoluble in acid solution, and the halides, perchlorate, nitrate, sulfate and sulfide to be soluble. 

Harvey, B.R. and Lovett, M.B. (1984) The use of yield tracers for the determination of alpha-emitting actinides in the marine environments. Nucl. Instr. Meth. Phys. Res., 223, 224—234. 

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. 

In laboratory tests using simulated HLW solution spiked with fission product tracers, Am and Cm, the denitration step proved to be a sensitive process, but Am/Cm recoveries of ca. 90% in the aqueous supernate could be realized under optimized conditions. Decontamination factors (DF) > 1000 for Zr, Nb, Mo, and 100 for Ru and Fe were obtained in the precipitation step. The solvent extraction cycle gave > 98% recovery of Am/Cm and DF > 10 for rare earths, Sr and Cs. Appreciable decontamination was also obtained for Zr/Nb (DF = 20), Ru (50), U (650), Pu (250), Np (800) and Fe (420). The ion exchange cycle served mainly for Am-Cm concentration and for removal of DTPA and lactic acid based on tests with europium as a stand-in for trivalent actinides, concentration factors of about 50 could be expected under optimized conditions. 

One possible application in which large amounts of rare earths and actinides would be processed occurs in some schemes for nuclear waste management. If it should prove to be advantageous to remove transplutonium elements from nuclear waste, for example, the recovery of Am and Cm from the much larger amounts of rare earths would be required. This problem has been investigated by the author in tracer tests with rare earth mixtures typical of fission products, using a heavy rare earth such as holmium as a stand-in for Am and Cm (Fig. 5). It is clear that the bulk of the holmium can be recovered in reasonable purity, and that the bulk of the lighter rare earths is effectively separated from the very small amount of heavy rare earths, Am, and Cm. 

The succeeding actinides (Cm, Bk, Cf, Es, Em, Md, No, Lr) mark the point where the list of isolated compounds tends to involve binary compounds (oxides, halides and halide complexes, chalcogenides, and pnictides) rather than complexes. Those studies of complexes that have been made are usually carried out in solution and, from Em, onwards, have been tracer studies. 

R. Guillaumont, J. P. Adloff A. Peneloux, P. Delamoye, Sub-tracer Scale Behaviour of Radionuclides, Application to Actinide Chemistry, Radiochim. Acta 54,1 (1991)... 

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. 

First, the trivalent actinide and lanthanide elements are separated from the other elements in the waste. In the second step, americium and curium are then separated from the lanthanide elements. Experimental studies have largely been laboratory-scale in which synthetic waste solutions and tracer levels of radioactivity were utilized. A few laboratory-scale experiments were made in hot cells on the coextraction of trivalent actinides and lanthanides. The two most promising methods investigated for co-removal of trivalent actinides and lanthanides are ... 

The differences in sorptive behavior of Th, Pu, U, and Np are evident by examining Table II. Plutonium and thorium isotopes at tracer concentrations (parts per billion, element mass/clay mass) were equilibrated for 24 hours with the < 2-pm fraction (clay) of a silt loam soil. The pH of the equilibration solutions was 6.5 and the aqueous phase contained Ca at a concentration of 5 mM. Both tetravalent actinides failed to remain 1n solution. Whether this is a direct function of sorption mechanisms or simply related to the solubility of the ions in solution is not distinguished by the results. Uranyl ion was not removed to the same extent as the tetravalent species. Neptunium(V) sorbed very poorly. It should be noted that while Np(V) is a mono-charged cation, Np02+ does not sorb like Na+. 

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