Uses of radiation dating
Animals and plants have a known proportion of Carbon-14 (a radioisotope of Carbon) in their tissues.
When they die they stop taking Carbon in, then the amount of Carbon-14 goes down at a known rate (Carbon-14 has a half-life of 5700 years).
The amount of carbon-14 in the atmosphere has not changed in thousands of years.
Even though it decays into nitrogen, new carbon-14 is always being formed when cosmic rays hit atoms high in the atmosphere.
When it decays it forms thorium-234 which is also unstable.
Finally, after a series of radioactive isotopes are formed it becomes lead-206, which is stable.
The age of the ancient organic materials can be found by measuring the amount of Carbon-14 that is left.
The most common tracer is called Technetium-99 and is very safe because it only emits gamma rays and doesn't cause much ionisation.
The method was developed by Willard Libby in the late 1940s and soon became a standard tool for archaeologists.The idea behind radiocarbon dating is straightforward, but years of work were required to develop the technique to the point where accurate dates could be obtained.Research has been ongoing since the 1960s to determine what the proportion of in the atmosphere has been over the past fifty thousand years.Some cancers are easier to treat with radiotherapy than others - it's not too difficult to aim gamma rays at a breast tumour, but for lung cancer it's much harder to avoid damaging healthy cells.Also, lungs are more easily damaged by gamma rays, therefore other treatments may be used.
Libby received the Nobel Prize in Chemistry for his work in 1960.