~(226)Ra, ~(210)Pb, ~(210)Bi and ~(210)Po deposition and removal from surfaces and liquids

摘要

Deposition of ~(226)Ra from water on nylon was investigated. Measurements performed for different pH and different radium concentrations in the water gave similar absolute activities deposited on the foil surface. Obtained results were used to estimate the amount of ~(226)Ra plated-out on the nylon scintillator vessel in the solar neutrino experiment BOREXINO during filling of the detector. Another problem studied in the frame of BOREXINO was the removal of ~(210)Pb from its organic liquid scintillator by applying distillation and water extraction. After several tests had been performed for both methods it was found that after the water extraction the initial lead content in the scintillator sample was reduced only accordingly to the ratio of the volumes of the applied liquids (simple dilution). In contrast to this, distillation was very effective providing in the best case a ~(210)Pb reduction factor higher than 100. Removal efficiencies of the long-lived ~(222)Rn daughters during etching from surfaces of standard and high purity germanium were investigated in the frame of the GERDA experiment, which aims to search for neutrino-less double beta decay of ~(76)Ge. The standard etching procedure of Canberra used during production of high purity n-type germanium diodes was applied to germanium discs, which had been exposed earlier to a strong ~(222)Rn source for its progenies deposition. In contrast to copper and stainless steel, ~(210)Pb, ~(210)Bi and ~(210)Po was removed from germanium very efficiently. An evidence of a reverse process was also observed-the isotopes were transferred from the etchant to the clean germanium surface.