First results from the Zurich Sea Water (ZSW) 236U intercomparison

Dr Marcus Christl1, Dr. Arne Bratkič6, Prof. Núria Casacuberta1, Dr Maxi Castrillejo1, Dr Elena Chamizo2, Dr Laura Fantozzi7, Dr Karin Hain3, Dr Joze Kotnik5, Dr Mu Lin4, Dr Mercedes López-Lora2, Dr Jixin Qiao4, Prof Hans-Arno Synal1, Dr Anne-Marie Wefing1

1ETH Zurich, Laboratory of Ion Beam Physics, Zurich, Switzerland, 2Centro Nacional de Aceleradores, Universidad de Sevilla, Seville, Spain, 3Faculty of Physics, University of Vienna, Vienna, Austria, 4Technical University of Denmark, Department of Environmental Engineering, Roskilde, Denmark, 5Jozef Stefan Institute, Department of Environmental Sciences, Ljubljana, Slovenia, 6University of Liège, Chemical Oceanography Unit, Liège, Belgium, 7National Research Council of Italy, Water research institute, Verbania, Italy

During the Fenice11 expedition to the Tyrrhenian Sea in 2011 several samples totaling more than 350L seawater were collected in for 236U/238U at ETH Zurich. Due to a chain of unfortunate circumstances the sample labels were not readable any more when they arrived at LIP (ETH Zurich). We decided not to discard the seawater but instead to prepare a large volume intercomparison sample for 236U.

All samples collected in 2011 were pumped through 0.45mm filters into a 400L plastic tank and then slightly acidified to pH3. After homogenization the seawater was filled into 35 ten liter plastic cubitainers. One or two cubitainers were sent out to each lab that intended to participate in the intercomparison study. The labs were asked to apply their standard sample processing procedures. The AMS labs were primarily asked to provide information on the 236U/238U ratio and (if possible) on the 236U and 238U concentrations of the sea water sample.

So far, several batches of the ZSW intercomparison samples were processed in four different chemistry labs and measured on four different AMS systems. While all four AMS labs returned information on the 236U/238U ratio of the intercomparison sample and most of them provided 236U and 238U concentrations, some additionally reported 233U/238U ratios and shared their results on Pu-, Am-, and Np-isotopic composition of the seawater sample.

While not all participating labs have yet reported their results this contribution intends to present the current status of the intercomparison study. A preliminary analysis shows that the different AMS labs reported very consistent results on the U-isotopic composition of the sea water sample. A preliminary consensus value for the 236U/238U ratio and the 236U and 238U concentrations will be presented. Also the results for the other actinides will be presented but the number of contributing labs is still too small for providing a consensus value.

The fact that the ZSW has been characterized by many different AMS labs makes the ZSW sample a valuable internal standard for quality control for the analysis of anthropogenic U-isotopes in seawater.


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Date

Nov 17 2021

Time

WEDNESDAY
1:00 pm - 1:25 pm