Conventional vs ams radiocarbon dating
Measuring 14C To obtain the radiocarbon age of a sample it is necessary to determine the proportion of 14C it contains.Originally this was done by what is known as “conventional” methods, either proportional gas counters or liquid scintillation counters.These newly formed 14C atoms rapidly oxidize to form 14CO..Photosynthesis incorporates 14C into plants and therefore animals that eat the plants.The radiocarbon age is determined by the equation where -8033 represents the mean lifetime of 14C (Stuiver and Polach, 1977), Asn is the activity in counts per minute of the sample and Aon is the counts per minute of the modern standard.
de Vries also postulated that the fluctuations were due to the production of 14C and how it changed during variations in cosmic ray production.
Three isotopes of carbon are found in nature; carbon-12, carbon-13 and carbon-14.
Carbon-12 accounts for ~99.8 % of all carbon atoms, carbon-13 accounts for ~1% of carbon atoms while ~1 in every 1 billion carbon atoms is carbon-14.
All radiocarbon ages are normalized to a 13C of -25‰ relative to PDB.
Calibration In the 1950s it was observed that the radiocarbon timescale was not perfect.