Carbon dating work
They also sampled artifacts from museums such as a piece of timber from Egyptian pharaoh Senusret III’s funerary boat, an object whose age was known by the record of its owner’s death.
In 1949, Libby and Arnold published their findings in the journal Science, introducing the “Curve of Knowns.” This graph compared the known age of artifacts with the estimated age as determined by the radiocarbon dating method.
Theoretically, if one could detect the amount of carbon-14 in an object, one could establish that object’s age using the half-life, or rate of decay, of the isotope.
In 1946, Libby proposed this groundbreaking idea in the journal Physical Review.
Top of page Carbon-14 was first discovered in 1940 by Martin Kamen (1913–2002) and Samuel Ruben (1913–1943), who created it artificially using a cyclotron accelerator at the University of California Radiation Laboratory in Berkeley.
Further research by Libby and others established its half-life as 5,568 years (later revised to 5,730 ± 40 years), providing another essential factor in Libby’s concept.
Finally, Libby had a method to put his concept into practice. The circular arrangement of Geiger counters (center) detected radiation in samples while the thick metal shields on all sides were designed to reduce background radiation.
The concept of radiocarbon dating relied on the ready assumption that once an organism died, it would be cut off from the carbon cycle, thus creating a time-capsule with a steadily diminishing carbon-14 count.Based on Korff’s estimation that just two neutrons were produced per second per square centimeter of earth’s surface, each forming a carbon-14 atom, Libby calculated a ratio of just one carbon-14 atom per every 10 carbon atoms on earth.Libby’s next task was to study the movement of carbon through the carbon cycle.Living organisms from today would have the same amount of carbon-14 as the atmosphere, whereas extremely ancient sources that were once alive, such as coal beds or petroleum, would have none left.For organic objects of intermediate ages—between a few centuries and several millennia—an age could be estimated by measuring the amount of carbon-14 present in the sample and comparing this against the known half-life of carbon-14.He reasoned that a state of equilibrium must exist wherein the rate of carbon-14 production was equal to its rate of decay, dating back millennia.