226Ra, 210Pb, 210Bi and 210Po deposition and removal from surfaces and liquids.

M Wójcik,G Zuzel

doi:10.1007/s10967-012-2180-5

Abstract

Deposition of 226Ra 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 226Ra 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 210Pb 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 210Pb reduction factor higher than 100. Removal efficiencies of the long-lived 222Rn 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 76Ge. 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 222Rn source for its progenies deposition. In contrast to copper and stainless steel, 210Pb, 210Bi and 210Po 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.

Highlights

Natural radioactive isotopes form the 238U chain pose in many cases the most relevant background source in experiments looking for rare nuclear processes, like interactions of lowenergy neutrinos, interactions of cold dark matter particles or neutrino-less double beta decay
Removal efficiencies of the long-lived 222Rn 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 neutrinoless double beta decay of 76Ge
Since the radon diffusion length in PC is relatively short [9] practically all atoms would decay close to their origin, which is the surface of the Inner Vessel

Summary

Introduction

Natural radioactive isotopes form the 238U chain pose in many cases the most relevant background source in experiments looking for rare nuclear processes, like interactions of lowenergy neutrinos, interactions of cold dark matter particles or neutrino-less double beta decay. One of its sources could be 222Rn produced by decays of 226Ra deposited on the IV surface during filling of the detector with ultra-pure water with the specific 226Ra activity of about 1 mBq/m3 [3]. It was filled with ultra-pure water, to which in the following step known activity of 226Ra (coming from a certified solution) was added. For the investigation of deposition efficiencies (transfer of isotopes from the etchant to the surface) of lead, bismuth and polonium on a clean high purity germanium surface the water to be used for preparation of the etching solution was contaminated by exposing it to a 222Rn-rich gas.

Results and discussion

Conclusions

Methods