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 turned into helium. Only 50 kg of tritium would be left. After another 12 years (a second half-life), half of what was left would decay. There would only be 25 kg of tritium left after 24 years from the start. That's one-quarter (half of half) of the 100 kg we started with.
Different radioactive materials have different half-lives. Carbon-14 has a half-life of nearly 6,000 years. The half-life of uranium-235 is more than 700 million years! On the other hand, the half-life of nitrogen-13 is less than 10 minutes!
Shop Windows to the Universe Science Store!
Our online store
includes issues of NESTA's quarterly journal, The Earth Scientist
, full of classroom activities on different topics in Earth and space science, as well as books
on science education!
You might also be interested in:
The text for this level hasn't been written yet. Please check the "Intermediate" or "Advanced" level of this page (click on the bar near the top of this page)....more
Isotopes are different "versions" of an element. All atoms of an element have the same number of protons. All hydrogen atoms have one proton, all carbon atoms have 6 protons, and all uranium atoms have...more
Some materials are radioactive. They give off radiation. When an atom of a radioactive substance gives off radiation, it becomes a new type of atom. This change is called radioactive decay. There are two...more
An element (also called a "chemical element") is a substance made up entirely of atoms having the same atomic number; that is, all of the atoms have the same number of protons. Hydrogen, helium, oxygen,...more
Carbon-14 is an isotope of the element carbon. All carbon atoms have 6 protons in their nucleus. Most carbon atoms also have 6 neutrons, giving them an atomic mass of 12 ( = 6 protons + 6 neutrons). Carbon-14...more
Carbon-14 dating (also called "radiocarbon dating") is used to determine the age of materials that contain carbon that was originally in living things. It is often used in archeology and some...more
Looking for online content that can be used for a climate change education course or module? Pages linked below can be used to support an introductory climate change education for either a unit or a full...more