tailieunhanh - Encyclopedia of Global Resources part 70

Encyclopedia of Global Resources part 70 provides a wide variety of perspectives on both traditional and more recent views of Earth's resources. It serves as a bridge connecting the domains of resource exploitation, environmentalism, geology, and biology, and it explains their interrelationships in terms that students and other nonspecialists can understand. The articles in this set are extremely diverse, with articles covering soil, fisheries, forests, aluminum, the Industrial Revolution, the . Department of the Interior, the hydrologic cycle, glass, and placer mineral deposits. . | 638 Isotopes radioactive Global Resources beled and unlabeled analytes compete for limited amounts of a molecule that binds the analyte very specifically. RIA is used worldwide in the determination of hormones drugs and viruses. The technique is so specific that concentrations in the picomolar region can be measured. Another major use of radioisotopes is as tracers that determine metabolic pathways transport processes and reaction mechanisms. A compound labeled with a radioactive isotope is introduced into the process and the radioactivity allows the compound to be followed through the mechanism. Pharmacokinetics is the study of the rates of movement and biotransformation of a drug and its metabolites in the body. Many kinetic parameters such as a drug s half-life in the body can be determined by using radiolabeled drugs and measuring radioactivity after some type of chromatographic separation of the parent drug from its metabolites. Radiopharmaceuticals are substances labeled with radionuclides that are used in the visualization of organs the location of tumors and the imaging of biochemical processes. This usage is based on the fact that a substance that is found in a healthy cell at a certain concentration has a different concentration in damaged cells. The particular isotope used depends on the organ or biochemical process under study. Radioisotopes are used in many ways in industr y. Gamma rays from cobalt 60 are used to examine objects for cracks and other defects. Radioisotopes can be used to measure thickness of all types of rolled materials and as tracers in locating leaks in pipes carr ying liquids or gases. The fill level of closed containers is monitored by absorption or scattering of radiation. In the chemical industry radioisotopes are used to indicate the completeness of a precipitation reaction. A radioisotope of the element to be precipitated is added to the solution to be precipitated. When the filtrate is free of radioactivity precipitation is .