Radioactive isotopes in carbon dating

Dedicated at the University of Chicago on October 10, 2016.In 1946, Willard Libby proposed an innovative method for dating organic materials by measuring their content of carbon-14, a newly discovered radioactive isotope of carbon.

He was inspired by physicist Serge Korff (1906–1989) of New York University, who in 1939 discovered that neutrons were produced during the bombardment of the atmosphere by cosmic rays.

Radiocarbon dating would be most successful if two important factors were true: that the concentration of carbon-14 in the atmosphere had been constant for thousands of years, and that carbon-14 moved readily through the atmosphere, biosphere, oceans and other reservoirs—in a process known as the carbon cycle.

In the absence of any historical data concerning the intensity of cosmic radiation, Libby simply assumed that it had been constant.

At the time, no radiation-detecting instrument (such as a Geiger counter) was sensitive enough to detect the small amount of carbon-14 that Libby’s experiments required.

Libby reached out to Aristid von Grosse (1905–1985) of the Houdry Process Corporation who was able to provide a methane sample that had been enriched in carbon-14 and which could be detected by existing tools.

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