A SCINTILLATOR PURIFICATION SYSTEM FOR A LARGE-SCALE SOLAR-NEUTRINO EXPERIMENT

An on-line purification system for a large-scale low-background liquid scintillation detector has been tested with the 5 t liquid scintillat ion detector, the Counting Test Facility at Gran Sasso. Counter-curren t water extraction removes polar and charged impurities such as ions a nd metal salts. Vacuum distillation of the entire scintillator has bee n applied to remove both radioactive impurities and chemical impuritie s that affect the optical properties of the scintillator. Filtration w ith a 0.05 mu m particulate filter removed suspended dust particles th at may contain U, Th and K, Nitrogen stripping was employed to remove dissolved water and noble gases (e.g. Kr-85) from the scintillator. Th e system has effectively reduced the internal back in the 5 t liquid s cintillation detector from 470 +/- 90 events/d to the detection limit of the detector (+/- 45 events/d) in the energy window 250 < E < 800 k eV. (C) 1998 Elsevier Science B.V. All rights reserved.