Tübingen 2003 – wissenschaftliches Programm
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HK: Physik der Hadronen und Kerne
HK 15: Poster-Sitzung: Kern- und Teilchen-Astrophysik
HK 15.3: Poster
Dienstag, 18. März 2003, 13:30–15:30, Foyer
Investigations of Ar and Kr in nitrogen for the Borexino experiment — •Grzegorz Zuzel, Gerd Heusser, Jürgen Kiko, and Hardy Simgen — Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany
39Ar and 85Kr are β-emitters and their continuous spectra overlap the expected spectrum of the electrons scattered by neutrinos in the Borexino detector. Since both isotopes can enter the detector through the trace amounts present in nitrogen they pose an important potential source of background (nitrogen is mainly used to remove 222Rn from the liquid scintillator). To get low background in the detector the activity of 39Ar and 85Kr should not exceed 1 count per day. Taking into account the abundance of 39Ar in Ar (about 1.4 Bq/m3) and 85Kr in Kr (about 1 MBq/m3) and their solubilities it is possible to find that we can tolerate 0.36 ppm Ar and 0.16 ppt Kr in nitrogen. Our goal is to find such pure gas on the market or develop suitable purification method. The latest is based on the liquid/gas chromatography on molecular sieve (of different pore sizes) or on charcoal. Commercially available and purified nitrogen is investigated by special tuned mass spectromer. The whole apparatus consists of a system of getter pumps for sample purification, ions source, ions focusing system and ions counting system. Measuring 1 ccm of nitrogen we can achieve the detection limit at the level of 1 ppb for Ar and 0.1 ppt for Kr. If necessary the sample volume can be increased to 5 or 10 ccm.