Ar and Kr concentrations in nitrogen as a measure of the 39Ar and 85Kr activities in connection with the solar neutrino experiment BOREXINO

Among other radionuclides, Ar-39 and Kr-85 are potential background sources in the solar neutrino detector BOREXINO. The expected low event rate requires that the nitrogen used in the experiment needs to have lower concentrations than 0.5 muBq/m(3) for Ar-39 and 0.2 muBq/m(3) for Kr-85, corresponding to volume concentrations in N-2 of 0.4 x 10(-6) m(3)/m(3) for Ar and 0.2 x 10(-12) m(3)/m(3) for Kr. Applying gas mass spectrometry and special care in the sampling technique we succeeded in finding the required purity. In addition, we studied the possibility to purify nitrogen from Kr by the adsorption method. (C) 2004 Elsevier Ltd. All rights reserved.