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
Gum over platinum acid, the print is washed in 1% potassium metabisulfite after proper development in water. Interested individuals should read up on the process before attempting, as the chromic acids are very dangerous to work with. The mechanics of the gum portion is not entirely known; what occurs is the exposed gum is hardened and becomes water-insoluble. Upon washing, the unexposed portions wash away, leaving the white paper exposed. The technique is related to platinum printing. Gum over platinum Gum over platinum is a historical chemical photographic process, which was commonly used in art photography. It is a very complex process, in