Radiocarbon dating sample processed
This discovery meant that there are three naturally occurring isotopes of carbon: Whereas carbon-12 and carbon-13 are stable isotopes, carbon-14 is unstable or radioactive.
Carbon-14 is produced in the upper atmosphere when cosmic rays bombard nitrogen atoms.
AMS technology has allowed us to date very small samples (such as seeds) that were previously undatable.
Since there are practical limits to the age range of the method, most samples must be younger than 50,000 years and older than 100 years.
Many laboratories now use liquid scintillation counters with the samples being converted to benzene.
All of these counter types measure the C-14 content by monitering the rate of decay per unit time.
Gas proportional counters soon replaced the solid-carbon method in all laboratories, with the samples being converted to gases such as carbon dioxide, carbon disulfide, methane, or acetylene.
Working with several collaboraters, Libby established the natural occurrence of radiocarbon by detecting its radioactivity in methane from the Baltimore sewer.