Well, why not try this
link for a start. When you're finished with all the sub-links, you're an expert in the field.
Anyway, for the interested bystanders, a short abstract about modern carbon dating, and those hanky panky words.
http://www.bbc.co.uk/history/archaeology/carbondating_1.shtml would pretty much explains the basics.
Carbon dating was developed in the 1950. Ik works simply with measuring heavy radioactive 14C atoms (normal –light- carbon is 12C). These isotopes come into being in the air due to a radiogenic reaction of nitrogen with cosmic radioactivity. It decays again with a half time of some 5700 years Consequently live tissue is supposed to have the same heavy 14C – 12C carbon ratio as the air, while dead tissue starts to loose the 14C, and the 14C – 12C ratio decreases. This can be used measuring it’s age.
In the early days, it was as simple as that. Just have a radioactivity geiger counter, count the ticks, assume that it is decaying 14C that you count. Do the math and there you are, the age of the thing. Well, in fact, the calculation brought anything but the correct age because of numerous complications, that have been neglected or could not be accounted for. The large errors were mostly attributed to sample contamination but this is something that really doesn’t happen that often.
So what are the real problems exactly?
- Other radioactive noise
- Variation of the concentration of carbon dioxide in the air, depending on the activity of sources and sinks
- The ratio of carbon isotopes changes in live tissue. Normally there are less heavy 14C atoms in tissues because the plants have a preference for light isotopes during photo synthetic processes.
- Variation of radiogenic production of heavy 14C. The more cosmic activity, the more 14C
- The temperature dependency of these fractionation processes also change those ratios of heavy atoms in the processes of building that particular tissue.
These problems have been addressed in the recent past resulting in more or less adequate solutions.
So what was done?
radioactive noise: counting 14C nowadays is done with a
mass spectrometer, not with radioactivity anymore, just like all the other isotope counting procedures, a tremendous improvement. (there is also a intermediate method called Liquid Scintillation Counting (LSC) but that has virtually been outdated already.
Now the actual ratio of heavy carbon (14C,) intermediate and stable carbon (13C) and light carbon (12C). Since 13C is also reacting differently to all those fractination processes but only half as explicit as 14C, we can calculate the original 14C content after all those processes.
Variation of carbon dioxide and all the processes that change the 14C concentration in the air are now adjusted by a calibration table that has been build by comparing carbon age with annual layer counting, annual layers of tree rings (dendrochronology) ice cores layers and yearly lake sedimentation layers (lacustrine varves). Differences up to 2500 years are normal in the ice age period.
The way the dating techniques are applied are reflected in the date details. Original geiger counting work is indicated with "carbon years" When the mass spectrometer is used and the 13C fractination technique is used, the age is expressed as for instance 1200 years "BP" (Before Present) And "present" being the year 1950. When also the calibration tables are used then the dating is expressed as 1200 Cal years BP. Curiously enough "cal years" is explained both as "calender years" and "calibrated years". Te correct answer is somewhere in the linx.
Since carbon dating is a very important instrument for basic dating we have put a lot of effort in correcting for all the errors, we could think of. Finally, we have a system with a reasonable degree of accuracy and trustworthiness.
