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What is tritium?
Tritium is a hydrogen atom that has an additional 2 neutrons in the nucleus. The Earth's atmosphere contains small amounts of tritium produced naturally when cosmic rays strike air molecules. Although tritium can be a gas, its most common form is in water. A weak radionuclide that decays into ordinary helium and beta particles, tritium has a half-life of 12.3 years. Small amounts of tritium are routinely produced here at Fermilab during particle beam collisions in our experiments.

What are the health risks of tritium?
As tritium decays into ordinary helium, it emits a low-energy beta particle. Beta particles deposit energy in the body. The beta particle from tritium has such low energy that it cannot penetrate the outer layer of human skin. Therefore, the main hazard associated with tritium is internal exposure through ingestion. The body excretes ingested tritium in about two weeks. Thus, tritium is only harmful if it is ingested in large amounts over long periods of time. High doses of tritium over a sustained period can cause cancer. To keep people safe, federal agencies set limits on the amount of tritium in water. Federal surface water standards set a limit of 2,000 picocuries per milliliter. The water of Indian Creek is surface water, not drinking water. Federal drinking water standards set a limit of 20 picocuries per milliliter.

How much tritium did we find?
We measured levels of tritium at 3.3 picocuries per milliliter in the water of Indian Creek just inside the Fermilab property. A picocurie is the unit used to specify how many tritium particles in a water sample decay into helium particles each second. Standard tests can detect levels of tritium in water that are larger than about 1 picocurie per milliliter.

Where did this material come from?
Tritium is a byproduct of accelerator operations here at Fermilab. Water with low levels of tritium is pumped out of the accelerator tunnels and used in our onsite industrial cooling systems and cooling ponds.

How did it get into the creek?
Indian Creek is a small creek that originates on the Fermilab site and leaves the lab at its southwest corner. We believe that a pipe connecting two cooling ponds near Indian Creek allowed water to escape from these ponds and ultimately to reach the creek. Samples taken from the cooling ponds adjacent to Indian Creek have shown low levels of tritium, comparable to those found in the creek. The investigation is ongoing.

What are we doing about it?
We are taking every possible step to make sure that we have identified all pathways of water containing tritium with the objective of reducing the level of tritium in Indian Creek to the lowest possible level.