The level of bomb carbon was about 100% above normal levels between 19.
The level of bomb carbon in the northern hemisphere reached a peak in 1963, and in the southern hemisphere around 1965.
Details Calibration of a radiocarbon age of 6550 ± 40 BP of a terrestrial sample from the Northern Hemisphere, using Int Cal04 calibration curve and Ox Cal program version 3.10.
Radiocarbon is a naturally occurring radioactive isotope of carbon.
Atoms of radiocarbon behave in the same way as any other carbon atoms except that they weigh slightly more and, after an average of some 5000 years decay to nitrogen.
The result is that radiocarbon and calendar ages are not identical, and the radiocarbon ages have to be converted to calendar ages using a calibration curve, which describes the atmospheric C concentration in the past measured in precisely and independently dated materials.
The current internationally-ratified calibration curve for terrestrial samples (e.g., woods, charcoals and macro-fossils) from the Northern Hemisphere is Int Cal04, which covers the past 26,000 calendar years (cal yr) (Fig. This curve is based on dendrochronologically-dated tree rings for the period 0-12,400 cal yr before present (BP, with 0 BP being AD 1950).