Nitrogen and argon radiopurity investigations for the Borexino and GERDA experiments

Borexino will look for low energy solar neutrinos while GERDA is designed to search for neutrinoless double beta decay of 76Ge. Radioactive noble gases of atmospheric origin present as traces in nitrogen or argon can significantly contribute to the background in these experiments. The most important are 39Ar, 85Kr and 222Rn. Nitrogen is used in Borexino for scintillator purification and blanketing, LAr will serve in GERDA as a passive/active shield and as a cooling medium for the Ge crystals. Concentrations of 39Ar, 85Kr and 222Rn in nitrogen must be below 0.5, 0.2 and 7 μBq/m3 (STP), respectively. Rn concentration in the argon used in GERDA should be below 0.5 μBq/m3 (STP). We found such extremely pure nitrogen on the market and simulated experimentally the supply chain between a supplier and a customer in order to prove that it is possible to keep the purity under control. We discuss the obtained results and applied measurement techniques. Results of Ar purification tests from 222Rn, its oncentration measurements in a gas of different quality are also shown and compared with those obtained for nitrogen. Rn emanation from storage tanks is also discussed. (orig.)