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
Reference materials for stable isotope analysis reference materials is problematic for applications that do not directly measure mass-resolved ion beams. Measurements of isotope ratios through laser spectroscopy or nuclear magnetic resonance are sensitive to the absolute abundance of isotopes and uncertainty in the absolute isotopic ratio of a standard can limit measurement accuracy. It is possible that these techniques will ultimately be used to refine the isotope ratios of reference materials. Measuring isotopic ratios by mass spectrometry includes multiple steps in which samples can undergo cross-contamination, including during sample preparation, leakage of gas through instrument valves, the generic category of phenomena called 'memory effects', and the