Improving the ATTA technique for krypton isotopes

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  • Published: Apr 11, 2014
  • Author: Steve Down
  • Channels: Atomic / UV/Vis Spectroscopy
thumbnail image: Improving the ATTA technique for krypton isotopes

A refined ATTA procedure for measuring radioactive krypton in small volumes of air will be useful in nuclear safety inspections, groundwater dating and atmospheric studies.

Krypton-81 is an isotope of krypton that is produced in space but not on Earth, neither naturally nor anthropogenically, and has been used to date groundwater and glacial ice which is 5000-1,000,000 years old. In contrast, krypton-85 is produced by nuclear fission and appears in the atmosphere mainly during nuclear fuel reprocessing. This isotope is useful for dating younger groundwater 2-50 years old, testing atmospheric transport models and tracing covert plutonium separation.

To measure these trace isotopes, they must be concentrated from large sample volumes to get sufficient sample but one recent technique, developed at Argonne National Laboratory in the US, has allowed the volume of the initial and refined samples to be reduced. It is atom trap trace analysis (ATTA), in which the krypton isotopes are captured in a magneto-optical trap and counted individually using their laser-induced fluorescence signals.

Now, Chinese scientists have refined the process further by developing a purification system built on closed-circuit cryogenic distillation combined with gas chromatography. It was described in Analytical Chemistry by senior reporter by Shui-Ming Hu from the University of Science and Technology of China, Hefei. This reduced the initial volume of air to as little as 1 L and the final volume of krypton gas to a few microlitres and provided recoveries from air of more than 90%. The technique was illustrated by analysing krypton-81 and krypton-85 in ambient air and in air extracted from air-solvated seawater, ice and deep and shallow groundwater.

One of the key advantages of the improved method is that the first step, cryogenic distillation, can be carried out in the field, facilitating subsequent transport since a pressurised container would not be required. The second principal advantage is the reduction in sample sizes.

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