Tracer radionuclides

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. 

Laboratory-fortified blanks and matrix spikes both test the analyst s ability to obtain the expected result. The extent to which the net radionuclide concentration of the fortified blank (corrected for yield and radioactive decay) deviates from the expected value for the tracer radionuclide concentration is a measure of analytical bias. Any consistent deviation from the expected value should be investigated to eliminate the cause. Typical causes are the wrong counting efficiency, an analytical problem with interchange between carrier and tracer, unreliable yield determination, or erroneous tracer radionuclide concentration. 

The tests of a capsule design may be performed with simulated radioactive material. The term simulated means a facsimile of a radioactive sealed source, the capsule of which has the same construction and is made with exactly the same materials as those of the sealed sonrce that it represents, but contains, in place of the radioactive material, a substance with mechanical, physical and chemical properties as close as possible to those of the radioactive material and containing radioactive material of tracer quantities only. The tracer should be in a form soluble in a solvent which does not attack the capsule. One procedure described in ISO 2919 [1] utilizes either 2 MBq of Sr-90 and Y-90 as soluble salt, or 1 MBq of Co-60 as soluble salt. When possible, shorter lived nnclides should be used. However, if leaching assessment techniqnes are used, care needs to be taken when interpreting the results. The effects of scaling will have to be introduced, the importance of which will depend upon the maximum activity to be contained within the capsule and also the physical form of the intended capsule contents, particularly the solubility of the intended capsule contents as compared with the tracer radionuclide. These problems can be avoided if volumetric leakage tests are used (see paras 603.3 and 603.4). Typically, tests for special form radioactive material are performed on full scale sealed sources or indispersible soUd material because these are not expensive and the results of the tests are easy to interpret. 

The massive production of radionuclides (radioactive isotopes) by weapons and nuclear reactors since World War II has been accompanied by increasing concern about the effects of radioactivity upon health and the environment. As illustrated in Figure 4.15 and by the specific examples shown in Table 4.7, radionuclides are produced as fission products of heavy nuclei of such elements as uranium or plutonium and are also produced by the reaction of neutrons with stable nuclei. The ultimate disposition of radionuclides formed in large quantities as waste products in nuclear power generation poses challenges with regard to the widespread use of nuclear power. Artificially produced radionuclides are also widely used in industrial and medical applications, particularly as tracers. Radionuclides may enter aquatic systems from both artificial and natural sources, and their transport, reactions, and biological concentration in aquatic ecosystems can be a water pollution concern. 

Studies with tracer radionuclides of the lighter homologs. Based on these results, new chromatographic column separations with ARCA II were elaborated [79]. In these experiments, most of the amines tested in the HCl system showed slow kinetics for back extraction into the aqueous phase, resulting in elution peaks with an unacceptable tailing of the radioactivities into the subsequent fraction, a feature that was not observed in the mixed HCl/HF system [75]. An acceptable... 

The U.S. Postal Service has many restrictions on the shipment of radioactive materials by mail for example, no package may contain more than 0.1 millicuries of the most common tracer radionuclides (Transport Groups III and IV, see Table App. 3.2), and the exposure rate at the surface of the package must be less than 0.5 milliroentgens per hour. The package must also have no significant surface contamination (defined as less than 220 dpm per... 

Decay products of the principal radionuclides used in tracer technology (see Table 1) are not themselves radioactive. Therefore, the primary decomposition events of isotopes in molecules labeled with only one radionuclide / molecule result in unlabeled impurities at a rate proportional to the half-life of the isotope. Eor and H, impurities arising from the decay process are in relatively small amounts. Eor the shorter half-life isotopes the relative amounts of these impurities caused by primary decomposition are larger, but usually not problematic because they are not radioactive and do not interfere with the application of the tracer compounds. Eor multilabeled tritiated compounds the rate of accumulation of labeled impurities owing to tritium decay can be significant. This increases with the number of radioactive atoms per molecule. 

In the marine environment, the numerous radionuclides can be classified into three broad categories based on their production or origin (1) those derived from the weathering of continental rocks, the primordial radionuclides, (2) those formed from cosmic radiation, the cosmogenic radionuclides, and (3) those artificially introduced into nature, the anthropogenic or transient radionuclides and tracers. The primordial radionuclides (e.g. Th, and U) were... 

The abundance of a trace element is often too small to be accurately quantihed using conventional analytical methods such as ion chromatography or mass spectrometry. It is possible, however, to precisely determine very low concentrations of a constituent by measuring its radioactive decay properties. In order to understand how U-Th series radionuclides can provide such low-level tracer information, a brief review of the basic principles of radioactive decay and the application of these radionuclides as geochronological tools is useful. " The U-Th decay series together consist of 36 radionuclides that are isotopes (same atomic number, Z, different atomic mass, M) of 10 distinct elements (Figure 1). Some of these are very short-lived (tj j 1 -nd are thus not directly useful as marine tracers. It is the other radioisotopes with half-lives greater than 1 day that are most useful and are the focus of this chapter. 

These are the most basic equations needed in order to utilize U-Th series radionuclides as time-dependent tracers. In turn, they can provide an apparent age of a process or a geochronological framework. 

For a radionuclide to be an effective oceanic tracer, various criteria that link the tracer to a specihc process or element must be met. Foremost, the environmental behavior of the tracer must closely match that of the target constituent. Particle affinity, or the scavenging capability of a radionuclide to an organic or inorganic surface site i.e. distribution coefficient, Kf, is one such vital characteristic. The half-life of a tracer is another characteristic that must also coincide well with the timescale of interest. This section provides a brief review of the role of various surface sites in relation to chemical scavenging and tracer applications. 

Radioactive particle tracking (RPT) can be used to map the velocity field by tracking the position of a single radioactive tracer particle in a reactor. The particle which may consist of a polypropylene shell contains a radionuclide that emits y-rays. 

Pfutzner, W. et al.. Intraoperative labeling of sentinel lymph nodes with a combination of vital dye and radionuclide tracer results in sentinel lymph node-positive patients, J. Deutsch. Dermatol. Ges., 4, 229, 2006. 

Cochran JK, Masque P (2003) Short-lived U/Th-series radionuclides in the ocean tracers for scavenging rates, export fluxes and particle dynamics. Rev Mineral Geochem 52 461-492 Cohen AS, O Nions RK (1991) Precise determination of femtogram quantities of radium by thermal ionization mass spectrometry. Anal Chem 63 2705-2708 Cohen AS, Belshaw NS, O Nions RK (1992) High precision uranium, thorium, and radium isotope ratio measurements by high dynamic range thermal ionization mass spectrometry. Inti J Mass Spectrom Ion Processes 116 71-81... 

---