The Carbon-14 within a living organism is continually decaying, but as the organism is continuously absorbing Carbon-14 throughout its life the ratio of Carbon-14 to Carbon-12 atoms in the organism is the same as the ratio in the atmosphere.
Once an organism dies it stops taking in Carbon in any form.
Smoke alarms contain a weak source made of Americium-241.
Alpha particles are emitted from here, which ionise the air, so that the air conducts electricity and a small current flows.
Half of the remaining Carbon-14 then decays over the next 5730 years leaving one fourth of the original amount.
By measuring the ratio of Carbon-14 in a sample and comparing it to the amount in a recently deceased sample its date can be determined.
The age of a rock can be calculated if its ratio of uranium to lead is known.
This is unstable and eventually decays to lead, which is stable.
We choose a source with a long half-life so that it does not need to be replaced often.There's a small amount of radioactive carbon-14 in all living organisms.When they die no new carbon-14 is taken in by the dead organism.The carbon-14 it contained at the time of death decays over a long period of time.By measuring the amount of carbon-14 left in dead organic material the approximate time since it died can be worked out.Radiocarbon or Carbon-14 dating is a technique used by scientist to date bones, wood, paper and cloth. It is produced in the Earth’s upper atmosphere when Nitrogen-14 is broken down to form the unstable Carbon-14 by the action of cosmic rays.