Radioactive tracer such as a cell or tissue, or as a flow tracer to track fluid flow. Radioactive tracers are also used to determine the location of fractures created by hydraulic fracturing in natural gas production. Radioactive tracers form the basis of a variety of imaging systems, such as, PET scans, SPECT scans and technetium scans. Radiocarbon dating uses the naturally occurring carbon-14 isotope as an isotopic label. Isotopes of a chemical element differ only in the mass number. For example, the isotopes of hydrogen can be written as H, H and H, with the mass number at top left. When the
Isotope analysis re-using of metals from different sources, limited reliable data and contamination of samples can be difficult problems in interpretation. All biologically active elements exist in a number of different isotopic forms, of which two or more are stable. For example, most carbon is present as C, with approximately 1% being C. The ratio of the two isotopes may be altered by biological and geophysical processes, and these differences can be utilized in a number of ways by ecologists. The main elements used in isotope ecology are carbon, nitrogen, oxygen, hydrogen and sulfur. Analysis of the ratio of O to O