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Description
About two tons of ultra pure copper has been produced as a material for construction of an internal shield of a low-background gamma spectrometer. Aurubis A.G. (Germany) has prepared a dedicated casting mould, selected the best possible raw material and cast the 2-ton block. In order to minimize the cosmic exposure the block was immediately transported and stored underground, 150 m below the surface in the Wieliczka Salt Mine (Poland). It was taken out only for short time for forging cutting and fabrication of the shield components.
The purity level of the coper was determined by analyzing the long lived U/Th isotopes with an ICP mass spectrometer, Ra-226 and other gamma emitters by high-sensitivity germanium spectrometry and Pb-210 by a dedicated technique based on Po-210 separation form Cu and determination of its activity. The results showed very high purity of the material and disequilibrium between different part of the U-chain.
