# What is the length of decay of carbon-14?

Jul 25, 2016

""^14C has a half life of $5730$ years $\pm 40$ years.

#### Explanation:

The half life of ""^14C is approximately $5730$ years $\pm 40$ years.

That means that in $5730$ years, half of a sample of ""^14C decays by beta emission into ""^14N, electrons and electron antineutrinos.

A small proportion of the nitrogen in our upper atmosphere is continuously being converted into ""^14C by cosmic rays. This is then included in the carbon compounds in living plants and animals. When they die, they stop absorbing carbon from the atmosphere, so the proportion of ""^14C to ""^12C starts to decrease, in accordance with the $5730$ year half life. So the proportion of ""^14C to ""^12C can be used to calculate the approximate time since a living organism died.

This assumes we have a good estimate for the proportion at the time the plant or animal was living. This has to be calibrated in order to give good estimates, but radiocarbon dating can provide useful dating for organic artefacts up to about $70 , 000$ years old.