Activities radionuclides

Both radiometric and mass spectrometric detection approaches have been used in automated radiochemical analysis, depending on the radionuclides of interest and the capabilities of the laboratory involved. The tradeoffs between radiation counting and atom counting have been described.14 16 17 Short-lived fission products may be advantageously detected with radiation detection, whereas long-lived (low specific activity) radionuclides can be determined with better sensitivity using ICP-MS. 

The utilization of gamma spectrometry for the quantitative determination of low level activity radionuclides in the natural environment is limited because the influence of the natural geochemical background is very strong, but the technique is often used in the study of airborne radioactivity [6, 7]. Low-level gamma spectrometry is used principally to determine the activity of nuclides such as Co, Cs, and Pb (Fig. 15.1). 

However, it is unlikely that humans could be exposed at hazardous waste sites to such high specific-activity radionuclides through the routes described in these studies. Table 2-9 lists the genotoxic effects of uranium in vivo and Table 2-10 lists the genotoxic effects of uranium in vitro. 

When employing high specific activity radionuclides, care should be taken to be sure that the iodine atom is in the form of iodide (I ). Oxidized forms of iodine, such as periodate or iodate which commonly occur in commercial preparations, are not incorporated into proteins by the procedures outlined here. 

Injection of a reductant such as sodium dithionite creates a reducing zone that may be effective in immobilizing uranium and other redox-active radionuclides. The technique is known as in situ redox manipulation (ISRM). It has been shown to be moderately effective for chromium and is proposed for use at the Hanford site for remediation of a uranium groundwater plume (Fmchter et al., 1996). 

The intention of this work was to measure the concentration of Li in examples of unirradiated reactor steel from which the likely activity concentration could be calculated using suitable values for the neutron flux. Calculated values could then be compared with the activities measured in examples of steel irradiated in a Magnox reactor. From this it was hoped to ascertain whether, given the concentration of Li, the activity could be reliably calculated or whether the effects of formation from ternary fission and subsequent diffusion would prevent this. Whilst the activity in activated steel was measured in a straight forward manner, the measurement of Li in steel was difficult. The conventional analytical techniques of ICP-OES and ICP-MS respectively failed to achieve an adequate detection limit, so alternative techniques were tried. SIMS was sensitive enough to detect Li but is a microscopic technique and so was prone to large uncertainties when used to predict the bulk concentration. NAA followed by radiochemical determination allowed the determination of but initially suffered interference from another activated radionuclide ( S). 

In the field of radiochemistry, and particularly with the use of high-specific-activity radionuclides, syntheses are almost uniformly done with an excess of unlabeled precursor and reagents with respect to the radionuclide, in this review fluorine-18. For that reason the efficiencies of reactions are generally given in terms of radiochemical yields instead of... 

The primary motivation for predicting the electrochemical properties of the coolant circuits of water-cooled nuclear power reactors has been that of explaining and predicting tenacious operating problems that include SCC and CF, mass transport of corrosion products and subsequent fouling of heat transfer surfaces, activity transport due to the movement of neutron-activated radionuclides from the core to out-of-core surfaces that are not shielded, and, in the case of PWRs, the axial offset anomaly (AOA). This latter phenomenon results from the deposition of boron... 

The specific activity is an important parameter to consider in radiolabehng and in vivo biodistribution of tracers. Cold molecules in low-specific-activity radiopharmaceuticals compete with radioactive molecules and lower the uptake of the tracer in tissues. Similarly, low-specific-activity radionuclides yield poor radiolabeling. 

In drinking water indirect indicators are allowed from the viewpoint of radiology, such as total volume activity alpha and total volume activity beta, which help to assess the occurrence of alpha or beta active radionuclides in waters without the necessity to identify actual radionuclides whose... 

During an DSA measurement, the carrier gas (air, nitrogen or other gas) carries the inert gas released by the sample situated in a reaction vessels into a detector for the inert gas. For example, to measure the a-activity of radon, a scintillation counter, ionization chamber or semiconductor detectors can be used. On the other hand, / -activity measurements of Kr, are made by Geiger-Miiller tubes. Gamma-active radionuclides of xenon can be measured by a gamma-spectrometer. The stable nuclides of inert gases are measured by a mass spectrometer. 

A convenient method for describing the radioactive decay is in terms of half-life , which is the time required for one-half of any starting amount of a radionuclide to undergo rearrangement. At the end of each half-life interval one-half of the starting material will be left unchanged. Also, the activity (the rate of decay, the number of decaying atoms per unit of time) will be one-half of the initial activity. Radionuclides may have half-lives from fractions of seconds to billions of years. 

In order to achieve high specific activity, radionuclides require chemical separation from the target material and induced radioactive byproducts. 

In chronometry, the age of the sample is defined not in terms of the decay of a parent nuclide, but rather as the in-growth of a daughter activity. Radionuclides that are linked to one another by the processes of radioactive decay have relative concentrations that can be calculated with the Bateman equations, which express the simple laws of radioactive decay and ingrowth. If there exists a time at which all the descendant radionuclides have been removed from the mother material, that time can be determined through the measurement of the relative concentrations of the mother and daughter nuclides at a later time. The time interval between the purification of the sample and the subsequent analysis of the sample is defined as the age of the material at the analysis time. The technique does not apply when the half-life of the daughter nuclide involved in the determination is significantly shorter than the elapsed time. 

In addition, the experimental difficulties involved in the analytical determination of very low concentrations of a pure P emitter of low energy in the presence of a large excess of other P , y—active radionuclides have to be mentioned. Since a direct radiation measurement of the activity in such a mixture is not possible, a sophisticated radiochemical separation has to be performed the details of which will be summarized below. The same problems arise in the determination of the content in irradiated nuclear fuel. On the other hand, both radionuclides show similar chemical and radiation properties so that their determination can be carried out using similar analytical procedures. 

Forster, W. O. 1968. Fallout radionuclides (Fe and Mn ) as indicators of salmon migration in the Northeast Pacific relative to neutron activated radionuclide (Zn ). Bull. Ecol. Soc. Am. 49(2) 72. 

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