those that form during chemical reactions without breaking down).The unstable or more commonly known radioactive isotopes break down by radioactive decay into other isotopes.The ratio of the original isotope and its decay product determines how many half-lives have occurred since the sample formed.
The half-life of isotopes from some sample elements: In the illustration above, 50% of the original mother substance decays into a new daughter substance.
After two half-lives, the mother substance will decay another 50%, leaving 25% mother and 75% daughter.
This process begins as soon as a living thing dies and is unable to produce more carbon-14.
Plants produce carbon-14 through photosynthesis, while animals and people ingest carbon-14 by eating plants. Scientists determine the ages of once-living things by measuring the amount of carbon-14 in the material.
When it decays to stable nickel, it emits two relatively high-energy gamma rays.
Today it is being replaced by electron beam radiation therapy systems.
A third half-life will leave 12.5% of the mother and 87.5% daughter.
In reality, daughter substances can also decay, so the proportions of substance involved will vary.
For biological objects older than 50,000 years, scientists use radioactive dating to determine the age of rocks surrounding where the material was found.
By dating rocks, scientists can approximate ages of very old fossils, bones and teeth.
Radioactive dating uses the decay rates of radioactive substances to measure absolute ages of rocks, minerals and carbon-based substances, according to How Stuff Works.