Tracer plutonium

To prepare a standardized plutonium tracer for use and compare its activity in 2 detector systems calibrated for alpha-particle counting efficiency. 

In this experiment, an alpha-particle spectrometer is used to determine the concentration of 239 +240pu. (Although both isotopes will be represented in the final determination, for simplicity we will refer to this result as 239Pu for the remainder of this experiment.) An appropriate tracer of plutonium, usually M2Pu, is added to the sample, as discussed in Experiment 6. The activity of the plutonium in the sample can be calculated from the measured 239Pu count rate and the ratio of the plutonium tracer (e.g., 242Pu) activity to its measured count rate. This plutonium concentration is reported in pCi or Bq per unit mass or volume of sample. 

Plutonium tracer solution, standardized. Concentration should be about 0.05 Bq/mL of 242Pu (238Pu tracer is used for some types of samples). 

Tracer techniques, for example, are used to obtain very small but representative and measurable samples of highly radioactive spent fuel solutions. One millilitre of the solution is then spiked with a known amount of uranium and plutonium tracer isotopes. A few microlitres of the spiked solution are dried and shipped to SAL. One to fifty nanograms of uranium or plutonium extracted from this tiny sample are sufficient for a complete analysis representing the composition of half a tonne of irradiated fuel with an accuracy of 0.3 to 0.5%. 

Ten different adsorbents were chosen for the present evaluation. They include four types of adsorbents (1) inorganic activated alumina and bone char adsorbents, (2) macroporous cation exchange resins, (3) macroporous anion exchange resins, and (4) chelating heavy metal removal agents. Equilibrium adsorption of Pu(IV) from actual PFP wastewater spiked with a Pu tracer was measured for each of the adsorbents. The plutonium tracer was required because the activity of plutonium in the wastewater was too low to be measured conveniently. Those adsorbents that adsorbed plutonium strongly were then tested in column flow-through experiments and the rate of plutonium adsorption was measured. 

The uranium purification contains two extraction-stripping stages. Plutonium tracers are removed by a reducing agent, e.g. U(IV) ... 

Release of plutonium from the sample s matrix into solution and the addition of plutonium tracers ... 

Argon-40 [7440-37-1] is created by the decay of potassium-40. The various isotopes of radon, all having short half-Hves, are formed by the radioactive decay of radium, actinium, and thorium. Krypton and xenon are products of uranium and plutonium fission, and appreciable quantities of both are evolved during the reprocessing of spent fuel elements from nuclear reactors (qv) (see Radioactive tracers). 

On the basis of these facts, it was speculated that plutonium in its highest oxidation state is similar to uranium (VI) and in a lower state is similar to thorium (IV) and uranium (IV). It was reasoned that if plutonium existed normally as a stable plutonium (IV) ion, it would probably form insoluble compounds or stable complex ions analogous to those of similar ions, and that it would be desirable (as soon as sufficient plutonium became available) to determine the solubilities of such compounds as the fluoride, oxalate, phosphate, iodate, and peroxide. Such data were needed to confirm deductions based on the tracer experiments. 

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... 

As mentioned above, early tracer work at the University of California in 1941 had established the existence of a lower oxidation state (IV and/or III state) and a higher state (VI and/or higher state), and the ultramicrochemical work late in 1942 and in 1943 had defined the existence of the IV and VI states. The III oxidation state was discovered early in 1944 by Connick and coworkers (1949), who actually worked with about 0.25 milligram of cyclotron-produced plutonium, at the University of California,... 

Studies of ligands which might provide specificity in binding to various oxidation states of plutonium seems a particularly promising area for futher research. If specific ion electrodes could be developed for the other oxidation states, study of redox reactions would be much facilitated. Fast separation schemes which do not change the redox equilibria and function at neutral pH values would be helpful in studies of behavior of tracer levels of plutonium in environmental conditions. A particularly important question in this area is the role of PuOj which has been reported to be the dominant soluble form of plutonium in some studies of natural waters (3,14). 

Pu-242 samples are available in enrichments ranging from 99.9+% to 95% production-grade material ranges from 85% to 95%. Uses are for the study of plutonium physical properties and as a mass spectroscopy tracer and standard. 

Livingstone et al. [87] carried out double tracer studies to optimise conditions for the radiochemical separation of plutonium from large volumes of seawater. 

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. 

The work had now progressed from the tracer to the microgram stage. Normally, this stage could have lasted for many years. At this time, however, plans were being made for the construction of a plant to produce plutonium on a large scale, and it was necessary to know the... 

Figure 3 illustrates the distributions found for Pu and Am when a mixed sample of these tracers was infiltrated into a large (30 cm x 30 cm) block of Bandolier tuff (6). The nuclide activities were determined simultaneously by coring sections of the tuff and represent the activity distributions in the rock. It is obvious that although the activities are both normalized at 100% at the surface the increased dispersion of the plutonium concentration during elution leads to an increase of almost an order of magnitude in its activity relative to Am at the 5-6 cm depth. It is highly unlikely that abnormal flow paths or movement of colloidal clay particles would discriminate between americium and plutonium therefore this experimental result tends to discount these possible types of mechanisms. However, a pure Pu polymer could carry the Pu more rapidly downstream. 

Various workers [32-34] have discussed mass spectrometric and other methods for the determination of plutonium in soils. Plutonium in soils has been quantified using 238plutonium as a yield tracer. Hollenbach et al. [36] used flow injection preconcentration for the determination of 230Th, 234 U, 239Pu and 240Pu in soils. Detection limits were improved by a factor of about 20, and greater freedom from interference was observed with the flow injection system compared to direct aspiration. 

The plutonium solubility increased in the presence of increased NaN03, NaOH, and NaA102 concentrations. According to the literature, Pu(V) should be the stable oxidation state in alkaline NOjT-NO solutions (8). It has been observed that the solubility of Pu(V) increases as tne NaOH concentration increases (8.11) probably this occured due to formation of the more soluble anionic hydroxide complexes of Pu(V) such as PuO,(OH)2 (11). Sodium nitrate and NaAlO, may have increased Pu(V) solubility through complexation. Sodium nitrate also may have increased plutonium solubility by oxidizing the less soluble Pu(IV), initially present in the tracer solids, to Pu(V). 

Foti, S. C. Freiling, E. C., "The Determination of the Oxidation States of Tracer Uranium, Neptunium, and Plutonium in Aqueous Media." Talanta 1964 11, 384-392. 

Figure 13.3 Alpha spectrum of oxidised and reduced plutonium species as separated by the neodymium fluoride technique (oxidised yield tracer 236Pu, reduced yield tracer 242Pu).

Foti, S.C. and Freiling, E.C. (1964) The determination of the oxidation states of tracer uranium, neptunium and plutonium in aqueous media. Talanta, 11, 385-392. 

Direct Dilution of a Certified Solution. When standard tracer solutions are purchased from commercial sources, detailed certificates must accompany them (see Section 11.2.6 in Radioanalytical Chemistry). Because the activity of the certified tracer solution usually is greater than needed for tracing individual samples, one or several sequential dilutions must be performed meticulously to produce the solution from which an aliquot will be pipetted into the samples. Dilutions should be prepared in a chemical form identical to the original solution with regard to type and concentration of acids and reagents to assure tracer solubility and stability. The analyst should perform dilutions by weight rather than by volume for precise work. The final dilution is usually planned to obtain a solution from which about 0.05 Bq is pipetted into a sample that contains that amount or less of plutonium analyte. 

This experiment illustrates use of M2Pu, but other suitable isotopes of plutonium (see Fig. 14.1 of this manual) that emit alpha particles may be calibrated. Suitability of tracer is based on the knowledge that the tracer radionuclide is not in the sample, or at a concentration so low - no more than 1 % of the tracer - that it will not interfere with yield determination. 

Compare the activity reported for the tracer solution with the activity obtained with the proportional counter and the alpha-particle spectrometer based on their respective counting efficiency (s) values, adjusted for sample volume and radioactive decay. Discuss whether the differences in activity are significant and decide which values are more reliable and should be associated with the tracer solution for subsequent measurements of plutonium. 

---