Today in class we talked about radioactive decay. Nearly all elements have radioactive isotopes. This means that the atom is unstable, and will eventually decay by emitting a particle, transforming the nucleus into another nucleus, or into a lower energy state. Decays happen in half-life’s. When a half-life passes (5730 years for carbon-14) only half of the material that was there in the start still exists. Here’s an example: Imagine carbon-14 was just made. At its half life, its mass will reduce to half the size it was when it was created. So, in turn, at the next half life carbon-14 would be only 25% of its original mass because at each half life, half the isotope has vanished. A chain of half-life’s occur (each depleting 50% of the isotope every half-life) until a stable nucleus is reached. When that stable nucleus is reached, many uses of radioactivity become unusable or unreliable, such as carbon-14 dating.
Carbon-14
Carbon-14 dating is commonly used in items that are 1,000 to 40,000 years old. This is how it works:
As the Earth’s atmosphere is bombarded by cosmic radiation, nitrogen is broken down into carbon-14. It falls through the atmosphere and is picked up by Earth’s atmosphere and spread around. Because it reacts identically to carbon-12 and carbon-13, carbon-14 becomes attached to plants using photosynthesys and becomes part of their molecular makeup. Animals eating those plants in turn absorb carbon-14 as well as the stable isotopes. This process of ingesting C-14 continues as long as the plant or animal remains alive. When the animal or plant dies, the carbon-14 decays, but because they are not radioactive carbon-12 and carbon-13 stay whole. By measuring how much of each isotope there is in the item in question, the age can be determined.
A very good calculator for finding values of half-lives is located here.
