Natural carbon-14 (C-14See 'Carbon-14'.) is generated by a (n,p)-reaction of neutrons of cosmic radiationRadiation originating directly or indirectly from extraterre... with nitrogen -14 in the upper atmosphere. Measurements of wood from the 19th century resulted in about 230 BecquerelUnit of activity of a radionuclide named after Henri Becquer... C-14See '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 energyAbility 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 C-14See 'Carbon-14'. to C-12 is reduced. In the mid-50s, this so-called Suess effect resulted in a five percent reduction of C-14See 'Carbon-14'. activityActivity 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 C-14See 'Carbon-14'. in the atmosphere to increase.
The natural concentration of C-14See 'Carbon-14'. in the human body leads to a C-14-activity of about 3 kBq. The resulting effective doseMeasure of a radiation effect to be indicated more precisely... amounts to 12 µSv/year.