Answer to Question #12757 Submitted to "Ask the Experts"

Category: Consumer Products — Watches, Clocks, and other Glow-in-the-Dark

The following question was answered by an expert in the appropriate field:


I am curious about what dangers might be associated with a tritium (3H) night sight used on a rifle or gun. If the gun's night sight rested upon the person's body, could this cause cancer? Second question, what is the danger from approximately 2 MBq of 3H being released in an accident, if the night sight was broken?


There is no danger from a tritium night sight resting upon a person. Tritium (3H) used in night sights, and in glow-in-the-dark watches and exit signs, is a radioactive material that only emits a very weak beta particle. The beta particle is an energetic electron ejected from the nucleus of the 3H, which has one proton and two neutrons. When 3H decays it becomes helium-3 (3He), which has two protons and one neutron and is not radioactive. The very weak beta particle from the 3H has such low penetrating power that it will not go through a sheet of paper or even a few millimeters of air.

If the night sight, with 2 MBq of 3H, was broken, the 3H released would not present a danger. Normally the 3H would be released and very little would be ingested, inhaled, or deposited on a person's skin. Any 3H deposited on the skin would be shielded from the beta radiation by the dead layer of skin. However, assume that all 2 MBq were ingested or inhaled by a person and stays inside the person as water (3H2O) and is naturally eliminated over time. The US Nuclear Regulatory Commission, in 10 CFR Part 20, Appendix B, Table 1, states that 80,000 µCi (approximately 3,000 MBq) would result in a "committed effective dose equivalent of 5 rems," equivalent to 0.05 Sv. So, an intake of 2 MBq of 3H might give a maximum dose of 3.3 × 10-5 Sv, which is 3.3% of the annual limit for a member of the public and about the same as a person's average annual dose from natural background radiation.

John P. Hageman, MS, CHP

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
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