Tritum has a half-life of 12.3 years. Pretend you started with
100 kilograms of tritium. After 12.3 years (one half-life), only
half (50 kg) of the tritium would be left (yellow lines). After
24.6 years (two half-lives), only one-quarter (25 kg) of the
original 100 kg of tritium would be left (blue lines). Click on
image for full size Original artwork by Windows to the Universe
staff (Randy Russell). Some materials are radioactive. Their
atoms give off radiation. When an atom gives off radiation, it
turns into a different kind of atom. That is called radioactive
decay. Some atoms decay very quickly, in seconds or minutes.
Others take a long time to decay... sometimes millions of years!
Scientists use the term "half-life" to describe how fast or slow
the radioactive decay is. Let's say you had 100 kilograms of
tritium. Tritium is a radioactive form of hydrogen. The half-
life of tritium is about 12 years. After 12 years, half of the
tritium would be "gone". It would have given off radiation and
decayed... and t