Radioactivity: A Very Short Introduction (Very Short Introductions) by Tuniz Claudio

Author:Tuniz, Claudio [Tuniz, Claudio]
Language: eng
Format: epub, mobi
Publisher: Oxford University Press
Published: 2012-07-25T21:00:00+00:00

Dating cells

Atmospheric nuclear weapons tests in the 1950s and 1960s injected a large amount of radiocarbon into the environment. During 1963–4, carbon-14 concentrations reached a level in the northern hemisphere that was 100% higher than that of the pre-nuclear era. After the signature of the Nuclear Test Ban Treaty in 1963, the concentration of radiocarbon has been decreasing with a half-life of 15 years, due to the exchange of carbon with the biosphere and the oceans. In a few years, environmental radiocarbon will return to pre-nuclear era levels. The features of this ‘bomb-pulse’ have been determined by reading the record of carbon-14 in the atmosphere, tree rings, sediments, and ice cores. This effect is somewhat reduced in the southern hemisphere.

Scientists use the radiocarbon bomb pulse to measure cell turnover rates on the timescale of years and decades in organisms that have lived after the 1950s. The chromosomes in cells incorporate carbon-14 from the environment, and the concentration of carbon-14 in a living cell corresponds to the level of carbon-14 in the atmosphere at the time it formed. The genomic DNA, which remains stable after the last mitosis, is used for AMS radiocarbon analysis.

The dating of brain cells through the carbon-14 bomb spike has shown that neurons are not generated after birth in the human cerebral neocortex, where language and intelligence is located. This conclusion is valid within the detection limits of the method, which is based on the analysis of the DNA extracted from 15 million cells, necessary to obtain 30 micrograms carbon for the AMS measurement at better than 1% precision. The method has the potential to map cell renewal for the whole human body and answer questions about the response of critical organs to ageing.

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