Radionuclides zirconium

The radionuclide zirconium-95 ( Zr) can be found among direct products of nuclear fission. Its radioactive decay leads to the daughter niobium-95 ( Nb). In the determination of Zr and Nb in samples of seawater and sea plants, the samples are mixed with oxalic acid in order that zirconium and niobium complexes can be formed in the presence of nitric acid. The oxalic acid is destroyed with potassium chlorate, and zirconium and niobium are precipitated as zirconium phosphate and niobic acid, respectively. Activities of rare-earth elements are removed, and zirconium is separated as barium hexafluorozirconate and ashed to zirconium pentox-ide. The niobium fraction is ashed to niobium pent-oxide. Both radionuclides are finally determined by y-ray spectrometry. 

NRC has issued an assessment of potential doses to the public associated with the distribution, use, and disposal of exempt products or materials containing low levels of source or byproduct material (Schneider et al., 2001) (see Section 4.1.2.5.2). In a case involving disposal of large volumes of zircon sand produced in processing of zirconium-bearing minerals, the estimated annual dose to a future on-site resident at a disposal site was 100 p.Sv, due to the elevated levels of thorium and uranium. In all other cases, however, the estimated annual dose was substantially less than 10 xSv. Since the volumes of exempt material were large in many cases, this analysis indicates that substantial volumes of waste that contains low levels of radionuclides are potentially exemptible. 

Pulsed research reactors, such as reactors of the Triga type, are especially designed for production and investigation of short-lived radionuclides. In these reactors the neutron flux is increased for about 10 ms to about 10 cm s by taking out the control rods (section 11.5). Due to the negative temperature coefficient of the zirconium hydride moderator, the outburst of power causes a sudden decrease of the moderator properties and shutting off of the reactor. After several minutes the effects have vanished and a new pulse can be started. The activities of radionuclides of various half-lives obtained with pulsed reactors are compared in Table 12.2 with those produced at constant neutron flux densities. The table shows that pulsed reactors are useful for production and investigation of radionuclides with half-lives < 10 s. 

Limitations, (i) As with other radionuclide-based ages, the terrestrial age of the sample must be known, (ii) Concentrations of Kr are quite low in most meteorites, typically just 5 X 10 atomg in chondrites. For this reason, Kr measurements are still scarce and their uncertainties can be relatively large, often —20%. (iii) Production rates for krypton isotopes may vary with the abundances of rubidium, yttrium, and zirconium relative to strontium. It should be understood that the original basis for the calculation of Pgi/Fgs was a set of relative cross-section measurements for the production of krypton from silver (Marti, 1967). 

The presence of high levels of the radionuclides of cerium, zirconium, ruthenium and transuranic elements in foods and environmental materials indicates the presence of hot particles which may be of special importance in considering exposure by inhalation and/or ingestion. 

DE Baetolo D, Cantone MC, Giussani a, Gae-lASCHELLi L, Roth P and Weenee E (2000) Determination ofbiokinetic parameters for ingestion of radionuclides of zirconium in animals using stable tracers. Radiat Environ Biophys 39 53-58. 

Refractory species (such as zirconium oxide) are incompletely atomized at the temperatures of a flame or a muffle furnace. If the radionuclide of interest may be in a refractory form, the material must be mixed with fusion reagents and melted at a high temperature. After cooling, the solidified melt is dissolved in a HNOj solution. Fusion mixtures that have been tested for many types of soil are listed in Table 4.2. Sample masses are limited by practical consideration of the final sample size, taking into consideration the large amounts of fusion reagents added to the sample. 

Based on measurements of air filters from 1965 to 1967 and rainwater samples from 1967, the Tc/ Cs ratio seems to be a factor of 10 higher than expected from the fission yield. The anomalous ratios of fission products observed in the atmosphere may partly be explained by fractionation of radionuclides during the detonation process. The precursors of Cs are gaseous or volatile elements, i.e., xenon and iodine, while the precursors of T c are refractory elements, i.e., zirconium and niobium, which are usually incorporated in radioactive particles. Thus, the Tc/ Cs ratio in the atmosphere may decrease with time after detonation due to the deposition of large radioactive particles. For deposited material releases of Tc with time should be expected due to weathering of particles. Howevei we cannot, at this stage, exclude additional sources contributing to releases of Tc to the atmosphere. 

W/ Re generators were described as early as 1966 using zirconium oxide (Lewis and Eldridge, 1966) and with aluminum oxide in 1972 (Mikheev et al. 1972), in spite of the excellent radionuclidic properties of Re, there was no practical use of this therapeutic... 

An intresting theranostic example of zirconium application was recently presented by McDevitt et A radioimaging probe based on Single Walled Carbon Nanotubes (SWNTs) functionalised with Zr-tagged des-ferrioxamine B [DFO] was synthesised and tested. Such constructed nanocomposite was able to deliver therapeutic and imaging radionuclide specifically to the vessels of a solid tumour and destroy it. 

For determination of the Ao-factor, gold was used as comparator, which was coirradiated as dilute Au-Al wire. This Au-Al wire should be coirradiated with each sample. It can, however, be converted to any comparator that is found suitable for coirradiation and that has been coirradiated with gold before. To determine the epithermal-to-thermal flux ratio, coinadiation of a zirconium monitor is suitable. The Ao-factors for 68 elements and their relevant gamma lines of 135 analytically interesting radionuclides have been determined and published by De Corte and coworkers. For nearly all of them, the uncertainly is <2%. An overview is given in Table 2 [31]-[33]. 

For P measurements with cascade impactors of all types, the radionuclide is isolated from the 0.1 M HCl leachate solution from the plates by precipitation of zirconium phosphate (Mullins and Leddicotte, 1962) and the /8-acAvity is determined using liquid scinAllation techniques. The purity of the P is checked by following the decay rate of the isolated /8-activity. 

The method described was developed by Mortier et al. (38) for the determination of boron in doped zirconium (100, 20, 1 and 0.5 pig/g of boron), in undoped zirconium and in zircaloy. The conditions given can be used for all these materials. For the 100 and 20 f g/g samples, however, shorter irradiation and measuring times may be used and an instrumental determination is feasible if 6 MeV protons are used. Table IV-3 summarises the most important nuclear reactions of zirconium and its impurities or alloying elements with protons. For low boron concentrations Be must be separated chemically from the radionuclides produced. 

Be must be separated from niobium, zirconium and yttrium radionuclides produced from zirconium and from V and Co produced from titanium and iron by the nuclear reactions given in Table IV-3. Anion exchange on Dowex 1 X 8 in 6 M hydrofluoric acid followed by precipitation of yttrium fluoride and barium beryllium fluoride was used. 

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