Radioactive test, characterization

The Characterization of Radioactive Particles from Nuclear Weapons Tests... 

Like all first-order processes, radioactive decay is characterized by a half-life, f]/2, the time required for the number of radioactive nuclei in a sample to drop to half its initial value (Section 12.5). For example, the half-life of iodine-131, a radioisotope used in thyroid testing, is 8.02 days. If today you have 1.000 g of I, then 8.02 days from now you will have only 0.500 g of remaining because one-half of the sample will have decayed (by beta emission), yielding 0.500 g of MXe. After 8.02 more days (16.04 total), only 0.250 g of will remain after a further 8.02 days (24.06 total), only 0.125 g will remain and so on. Each passage of a half-life causes the decay of one-half of whatever sample remains, as shown graphically by the curve in Figure 22.2. The half-life is the same no matter what the size of the sample, the temperature, or any other external condition. 

There are currently several methods for analysis of the amplified target DNA. For HIV-1, liquid hybridization with radioactively labeled probes is used (K12). Tests for HLA genes and sickle cell anemia utilize the reverse dot-blot format with a nylon membrane (S3). Each clinical research format has a well-characterized detection method defining the optimum probe concentration, the hybridization times and temperatures, as well as the concentrations of indicator reagents. Table 5 describes the optima and tolerances of a nonradioactive dot-blot assay that uses biotinylated probes and detection by a chemiluminescent substrate and a strepta-vidin-HRP conjugate. 

The use of hypothesis testing to define the LLD has been evaluated previously (1-4), Two states of any measurement system composed of normally distributed random uncertainties are considered the null hypothesis state in which the samples contain no net radioactivity and the distribution about the net count of zero is characterized by the Hean (v ) and the standard deviation (Oq) and, the LLD state (Currie s "alternate hypothesis" in the NUREG) in which the distribution about the net counts at the LLD is characterized by the mean (vq) and the standard deviation (oq). The ultimate question for any sample data is "Which state is most, consistent with the data ". In making this decision, there is a chance that we will falsely conclude the data is part of the distribution about the LLD or that we will falsely conclude the data is part of the distribution about the net count of zero. These risks are defined by the probabilities a and P respectively. These risk probabilities may be chosen at any level... 

In preclinical studies, histopathology has traditionally been the primary method of demonstrating GI injury. While this remains the most reliable way to detect and characterize tissue damage at the conclusion of a study, the need for realtime detection remains. The literature abounds on biomarkers of GI disease, though most are nonspecific and/or insensitive. The field is improving, however, and we describe several biomarkers here that have some possible or demonstrated utility in preclinical species. Many orally administered probe tests, such as the sucrose breath test, are not considered to have utility in preclinical studies due to the requirement for radioactive tracers and are therefore not covered. 

In 1948 chemists working for Glaxo in England and for Merck in the United States isolated a crystalline compound from liver that clinical tests proved to be the extrinsic factor. Because the factor proved to be a nutritional requirement, the Americans called it vitamin B12. Isolation of vitamin B12, the discovery that it contains cobalt, and the substitution of radioactive cobalt for the stable isotope made characterization of the intrinsic factor much easier, for it was no longer necessary to find a patient in relapse and then to exhaust his usefulness in one time-consuming test of a single preparation. ... 

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