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To determine the uranium content, several methods have been used.One method is by neutron irradiation, where the sample is irradiated with thermal neutrons in a nuclear reactor, with an external detector, such as mica, affixed to the grain surface.Using a form of krypton, a chemical element created when cosmic rays hit the planet, scientists have developed a new technique to more accurately date ancient Antarctic ice which could help them understand the forces that have triggered ice ages, according to a study published in Proceedings of the National Academy of Sciences.“The ultimate thing we would like to know is what the climate was like in the past…because that helps us understand what the climate might be like in the future,” said Edward Brook, co-author of the report.Studying the contents of very old ice could help scientists understand how the relationship between greenhouse gases, which speed up global warming, and climate has evolved over time, he added.Radiometric krypton dating uses krypton-81, a radioactive isotope of krypton—one of the rarest particles on Earth—that is produced by cosmic rays blasting into the Earth, which are stored in air bubbles within Antarctic ice.The gas traveled from Antarctica to Switzerland, where experts separated the krypton from the rest of the air, and then to the Argonne lab, where scientists measured the krypton isotopes, according to Brook.
Other techniques to date old ice use the ice around a sample to approximate the age, and are not as accurate, said Brook.The answer might have implications for how scientists understand and predict the future of climate.“Dating old ice accurately will help us build a better picture of how global warming might evolve,” said Brook.Fission-track dating is a relatively simple method of radiometric dating that has made a significant impact on understanding the thermal history of continental crust, the timing of volcanic events, and the source and age of different archeological artifacts.Now, scientists can begin looking for more ancient ice than the oldest available ice core that has been found so far, which is approximately 800,000 years old, according to Christo Buizert, a postdoctoral researcher at Oregon State University and the lead author of the study.
Scientists are hoping that the new technology will help them more accurately date ice back as far as 1.5 million years.
Because etched tracks are relatively large (in the range 1 to 15 micrometres), counting can be done by optical microscopy, although other imaging techniques are used.