Natural carbon-14 (See 'Carbon-14'.) is generated by a (n,p)-reaction of neutrons of Radiation originating directly or indirectly from extraterre... with nitrogen -14 in the upper atmosphere. Measurements of wood from the 19th century resulted in about 230 Unit of activity of a radionuclide named after Henri Becquer... See 'Carbon-14'. per kilogram carbon. This natural (pre-industrial) ratio between the radioactive carbon-14 and the stable carbon-12 in the atmosphere is today influenced by two opposed effects:
The massive generation of CO2 by burning fossil C-14-free Ability to do work or diffuse heat. The unit of energy is th... carriers leads to an increase in the proportion of C-12. Thus the pre-industrial ratio of See 'Carbon-14'. to C-12 is reduced. In the mid-50s, this so-called Suess effect resulted in a five percent reduction of See 'Carbon-14'. Activity is the term used to characterise the number of nucl... per kg carbon in the atmosphere.
Nuclear weapon tests in the atmosphere and disposal from nuclear facilities cause the proportion of See 'Carbon-14'. in the atmosphere to increase.
The natural concentration of See 'Carbon-14'. in the human body leads to a C-14-activity of about 3 kBq. The resulting effective Measure of a radiation effect to be indicated more precisely... amounts to 12 µSv/year.