Extraction of single 71Ge atoms from the gallium target of a Ga-Ge neutrino detector

Abstract

A method has been developed for the extraction of single 71Ge atoms from the gallium target of a Ga-Ge neutrino detector. The key features of this chemical process stem from the extremely low content of the element to be extracted in the sample (n × 10−27 at %), the large sample weight (up to n × 103 kg), the limited time available for the extraction and measurement of the extracted atoms (≤20 h), and small permissible loss (≤0.1%) of the target material at high degrees of 71Ge extraction (≥90%). The method involves forced generation and maintenance of a disperse system of liquid gallium droplets with an oxide surface film in an acid-peroxide solution. The small droplet size ensures a rapid 71Ge transfer from the bulk target to a small amount of gallium oxide. The 71Ge passes from the oxide film to the solution, is concentrated, and converts to germane, which is delivered to a proportional counter. We have assessed the completeness of germanium extraction in relation to process conditions. The results, in particular the completeness of extraction, have been verified in experiments with Ga + Ge mixtures at germanium concentrations of 10−4 and 10−17 to 10−16 wt %. The adequacy of the approaches used to develop the technology of the Ga-Ge detector is supported by satisfactory agreement between the solar neutrino fluxes obtained with gallium and gallium-chloride detectors.