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Abstract:
Experiments in sub-MeV particle astrophysics pose stringent requirements on the radioactive background. During the development of BOREXINO major progress was achieved in the reduction and determination of the background, especially that due to Ra-226 and Rn-222. Employing charcoal adsorption and internal proportional counting Rn-222 activities in the range of 50 muBq are routinely detected. Solid, liquid or gaseous samples as well as large volumes in the detector periphery are analysed.