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Dating Groundwaters with Tritium

Ground Water Hydrology

  1. Stephen M. Testa

Published Online: 15 JUL 2005

DOI: 10.1002/047147844X.gw151

Water Encyclopedia

Water Encyclopedia

How to Cite

Testa, S. M. 2005. Dating Groundwaters with Tritium. Water Encyclopedia. 5:69–72.

Author Information

  1. Mokelumne Hill, California

Publication History

  1. Published Online: 15 JUL 2005


Tritium (3H) is one of the most common radioisotopes used to identify the presence of modern groundwater recharge and estimate apparent groundwater ages (1). Tritium, a short-lived radioactive isotope of the element hydrogen, has one proton and two neutrons. Tritium emits only a very weak beta particle and has a half-life of 12.43 years. Although tritium can occur as a gas, its most common form is in water because, like nonradioactive hydrogen, radioactive tritium readily reacts with oxygen to form water, which allows groundwater to be dated. As tritium replaces one of the stable hydrogens in the water molecule, (H2), it is referred to as the molecule HTO, or tritiated water (T20). Similarly to water, tritium is colorless and odorless.

Tritium is produced naturally in both the atmosphere and hydrosphere of the earth when cosmic rays strike air molecules, notably by the interaction of 14N with cosmic ray neutrons.


  • chlorofluorocarbons;
  • groundwater;
  • groundwater age dating;
  • helium;
  • hydrogen;
  • meteoric water;
  • nuclear weapons;
  • radioisotope;
  • recharge;
  • source identification;
  • tritium;
  • tritium unit