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Research ESRIG - Energy and Sustainability Research Institute Groningen Events

ESRIG-EES colloquium: Andrea Scifo, MSc EES student

When:Tu 07-11-2017 at 16:00
Where:5159.0010 (Energy Academy Building, Nijenborgh 6)

Title: The Radiocarbon Signature of Past Radiation Events.

Radiocarbon (14C) is naturally present on Earth due to continuous formation in the upper atmosphere via cosmic ray bombardment; once produced it becomes part of the global carbon cycle. Given its radioactive nature, it has been used for dating purposes since 1949. By measuring the 14C/12C ratio of the sample and correcting it on the basis of the history of changes in atmospheric concentrations of the isotope a date can be produced. Until recent times, it was thought that fluctuations of 14C activity between one year and the next would be insignificant. However, in 2012 Miyake et al. reported a rapid and strong (about 12‰) increase in 14C concentration in Japanese cedar trees between A.D. 774 to 775. This result was soon confirmed by several other laboratories, who analysed different wood samples from different locations, highlighting also the worldwide synchronicity of this event. At the moment, intense Solar Particle Events are thought to be the most probable cause for this kind of event, but there is still uncertainty. In this project, I was provided with two different wood samples. I analysed their radiocarbon content, after pre-treating them with a novel sample preparation method. The first one acted as a test for this method, since it contained growth rings dated between A.D. 770 and 780 via dendrochronology. The results showed an increase almost identical to the one observed by Miyake, confirming the suitability of the pre-treatment method. The second one was previously analysed by Haesaerts et al. (2014), who observed a large fluctuation in the radiocarbon dates they obtained on it. I repeated the measurement, this time with single-year resolution and with higher isotopic precision, in order to understand the reason for this fluctuation. The results showed a very large single-year radiocarbon increase, which suggests that it might be a new candidate for this kind of event, but a more thorough study will be needed in order to confirm that.