Naturally occurring radioisotopes:
Chlorine-36: Used to measure sources of chloride and the age of water (up to 2 million years)
Carbon-14: Used to measure the age of water (up to 50,000 years)
Tritium (H-3): Used to measure 'young' groundwater (up to 30 years)
Lead-210: Used to date layers of sand and soil up to 80 years
Artificially produced radioisotopes:
Used in backscatter gauges, smoke detectors, fill height detectors and in measuring ash content of coal.
Used for radiotracer technique for identification of sources of soil erosion and deposition, in density and fill height level switches.
Silver-110m, Cobalt-60, Lanthanum-140, Scandium-46, Gold-198:
Used together in blast furnaces to determine resident times and to quantify yields to measure the furnace performance.
Used for gamma sterilisation, industrial radiography, density and fill height switches.
Gold-198 & Technetium-99m:
Used to study sewage and liquid waste movements, as well as tracing factory waste causing ocean pollution, and to trace sand movement in river beds and ocean floors.
Strontium-90, Krypton-85, Thallium-204:
Used for industrial gauging.
Zinc-65 & Manganese-54:
Used to predict the behaviour of heavy metal components in effluents from mining waste water.
Iridium-192, Gold-198 & Chromium-57:
Used to label sand to study coastal erosion
Ytterbium-169, Iridium-192 & Selenium-75:
Used in gamma radiography and non-destructive testing.
Used as a tracer to study sewage and liquid wastes.