Radionuclide-based method

Optical imaging offers several key benefits over PET. PET radiopharmaceuticals generally need to be made on-site and require appropriate radiation safety precautions. In contrast, bioluminescence studies are simpler to conduct because the substrates are commercially available and readily prepared. Furthermore, multiple animals can be smdied at the same time, and they can be studied quickly because image acquisition times are typically short. The interval between smdies that involve repetitive imaging is also short, unlike radionuclide-based methods, which require time for radioactive decay. Finally, both the reporter gene products and substrates used in bioluminescence studies (e.g., luciferases and D-luciferin) appear to be nontoxic to mammalian cells. This is a theoretical advantage over radionuclide-based methods, which depend on the use of ionizing radiation (22). 

Radionuclide-based screening for protein kinase substrates is a quick and effective method for determining peptide substrates for protein kinases.28-31 The method presented here is based on the screening of random synthetic combinatorial peptide libraries with a protein kinase and is divided into two main parts (1) the phosphorylation of the peptide bead library and (2) the recovery and characterization of positive beads. 

The last two decades have seen an increased interest in the use of supercritical fluids in separation science. Supercritical C02 has often been employed as a naturally occurring medium for the separation, purification, and determination of organic substances in environmental samples. However, there are only limited reports on the use of supercritical fluid as solvent in the separation of metal ions from solutions as well as various solid matrices. The supercritical fluid extraction (SFE) technology offers several advantages over conventional solvent-based methods, including the ability to extract radionuclides directly from solids, easy separation of solutes from C02, and minimization of waste generation. It can easily be removed from the extracted substances by degasification under atmospheric pressure and temperature. 

Properly, radionuclide concentrations are reported in units consistent with the method used for their determination. A radioanalytical technique such as liquid scintillation or alpha spectrometry yields a result expressible in terms of radioactivity. A mass-based analytical technique, such as laser phosphorimetric determination of U(aq) yields mass-based concentrations such as micromoles per liter. Detection limits using radioactivity measuring methods are often many orders of magnitude lower than those possible with mass-based methods (cf. Krieger and Whittaker 1980). For example, 100 pCi/L of Rn, a concentration easily determined by liquid scintillation, equals 2.93 x 10" M, or approximately 1.76 x 10 atoms/L. At standard temperature and pressure, this amount of radon has a minuscule partial pressure of 6.6 x 10" bar, assuming ideal gas behavior. 

One of the limitations of the portable field survey instruments in the measurement of americium is that their quantitative accuracy depends on how well the lateral and vertical distribution of americium in the soil compares with the calibration parameters used. These methods can provide a rapid assessment of americium levels on or below surfaces in a particular environment however, laboratory-based analyses of samples procured from these environmental surfaces must be performed in order to ensure accurate quantification of americium (and other radionuclides). This is due, in part, to the strong self absorption of the 59.5 keV gamma-ray by environmental media, such as soil. Consequently, the uncertainty in the depth distribution of americium and the density of the environmental media may contribute to a >30% error in the field survey measurements. Currently, refinements in calibration strategies are being developed to improve both the precision and accuracy (10%) of gamma-ray spectroscopy measurements of americium within contaminated soils (Fong and Alvarez 1997). 

Pollution of soils and waters by human activities is an important and widespread problem. This pollution by, organic and inorganic substances can affect individual organisms, human populations, and ecosystems, each in its own unique way. In particular former military installations, often used for weapons production and nuclear power plants represent a ongoing and substantial threat to environment and human health because of the specific pollutants that can be released Solvents, explosives, fuels, radionuclides, heavy metals, and metalloids all have been identified in the environment around these installations. Remediation technologies for these contaminated sites have been developed based on conventional systems utilising physical and chemical treatments, such as excavation and incineration, pump-and-treat methods, ultraviolet oxidation, soil washing, etc. 

Age of Rocks. In the table of nuclides given under Chemical Elements, there are listed a number of naturally occurring radionuclides with long half-lives. From these known half-lives, the geological age of a rock may be calculated. One method of making this estimate is based upon the amount of radionuclide and its daughter nuclide contained in the rock. This method is based upon various assumptions, which may be stated as follows ... 

The dating methods discussed up to now have been based on the use of long-lived radionuclides that are present in nature. Dating is also possible using extinct radionuclides, that is, nuclei whose half-lives are so short that if they existed at the time of formation of our solar system, they would have decayed away essentially completely by now. The nuclides 129I t /2 = 1.57 x 107 y) and 244Pu t /2 = 8.08 x 107 y) are noteworthy examples of this type of nuclide. 

Column-based separation approaches are well suited for the isolation of radionuclides from complex sample matrixes in a rapid automated format. The development of automated radioanalytical methods is, in fact, closely coupled to the availability of extraction chromatographic materials. In this review, we will focus on the... 

The development of solvent-impregnated resins and extraction-chromatographic procedures has enabled the automation of radiochemical separations for analytical radionuclide determinations. These separations provide preconcentration from simple matrices like groundwater and separation from complex matrixes such as dissolved sediments, dissolved spent fuel, or nuclear-waste materials. Most of the published work has been carried out using fluidic systems to couple column-based separations to on-line detection, but robotic methods also appear to be very promising. Many approaches to fluidic automation have been used, from individual FI and SI systems to commercial FI sample-introduction systems for atomic spectroscopies. 

Risk Index for Mixtures of Hazardous Substances. For the purpose of developing a comprehensive and risk-based hazardous waste classification system, a simple method of calculating the risk posed by mixtures of radionuclides and hazardous chemicals is needed. The method should account for the linear, nonthreshold dose-response relationships for radionuclides and chemical carcinogens (stochastic effects) and the threshold dose-response relationships for noncarcinogenic hazardous chemicals (deterministic effects). 

The basic framework for the waste classification system developed in this Report is depicted in Figure 6.1. Starting with the objectives that the classification system should apply to any waste that contains radionuclides or hazardous chemicals and that all such waste should be classified based on risks to the public posed by its hazardous constituents, the fundamental principle of the proposed system is that hazardous waste should be classified in relation to disposal systems (technologies) that are expected to be generally acceptable in protecting public health. This principle leads to the definitions of three classes of waste, and to quantification of the boundaries of the different waste classes based on considerations of risks that arise from different methods of disposal. The boundaries normally would be specified in terms of limits on concentrations of hazardous substances. At the present time, nearly all hazardous and nonhazardous wastes are intended for disposal in a near-surface facility or a geologic repository, and these are the two types of disposal systems assumed in classifying waste. The three waste classes and their relationship to acceptable disposal systems are described in more detail in Section 6.2. 

However, given the current state of knowledge and methods of dose-response assessment for substances that cause stochastic responses, there appear to be important technical and institutional impediments to the use of either incidence or fatalities exclusively. Data on radiation-induced cancer incidence and chemical-induced cancer fatalities for use at the low doses and dose rates relevant to health protection are not readily available, and current regulatory guidance calls for calculation of cancer incidence for hazardous chemicals. Since use of a common measure of response for all substances that cause stochastic responses may not be practical in the near term, both measures (fatalities for radionuclides and incidence for hazardous chemicals) could be used in the interest of expediency. The primary advantage of this approach is that the measures of stochastic response for radionuclides and hazardous chemicals would be based on the best available information from studies in humans and animals, and it would involve the fewest subjective modifying factors. This approach also would be the easiest to implement. 

Exempt Waste. The class of exempt waste embodies the concept that there are amounts of hazardous substances in waste which are so low that the associated risks to the public for any method of disposal generally would not be of concern. Thus, if waste that contains radionuclides were classified as exempt, the waste could be disposed of as if it were nonradioactive, and similarly for waste that contains hazardous chemicals or mixtures of the two. Further, mixed wastes that contain exempt amounts of radionuclides could be managed based on their hazardous chemical content, and vice versa. 

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