tritium clock Tritium (T) is a naturally occurring radioactive isotope (³H) of hydrogen (²H), having two neutrons and one proton in the nucleus. The isotope decays (half-life = 12.26 years, see DECAY CONSTANT) by beta emission (see BETA DECAY) to stable helium (³He) and this can be used to measure the age of water samples back to approximately 30 years. Tritium is produced in the upper atmosphere by the interaction of fast cosmic-ray neutrons with stable ¹⁴N. The tritium combines with hydrogen and oxygen to form HTO, which is then dispersed throughout the hydrosphere. The natural production rate of tritium is 15–45 atoms/min/cm² of the Earth's surface. In some experiments, artificially produced tritium has been introduced into ground-water and used to trace and time underground movements. It can also be used to measure and time rates of mixing in oceanic current systems.

tritium clock The decay of the radioactive isotope of tritium (T), which is used to measure the age of water up to about 30 years and to monitor the movement of groundwater. The tritium is produced naturally in the upper atmosphere by the action of fast cosmic-ray neutrons on ¹⁴N and combines with hydrogen and oxygen to form HTO, which is then dispersed throughout the hydrosphere. The tritium has a half-life of 12.26 years.