Isotopic analysis of germanium by thermal ionization mass spectrometry

Abstract

Detectors of high purity germanium enriched in the isotope 76 are employed to detect neutrino double-β decay. To better characterize the isotope composition of ⁷⁶Ge-enriched materials a new sample loading method has been developed for isotope ratio measurements of germanium using thermal ionization mass spectrometry (TIMS). Ge powder is mixed with commercial cellulose nitrate adhesive previously diluted with acetone and loaded on the rhenium filament (about 0.3 mg of germanium). The advantage of this solid Ge loading method is that it avoids difficulties with Ge dissolution encountered in other mass spectrometric techniques. In the absence of certified reference material of known isotopic composition, a sample of natural germanium, assuming that it has the representative isotopic composition of natural germanium published by IUPAC, was measured to calculate the mass fractionation factor which was applied to the analysis of two enriched samples (84.10 and 82.60% of ⁷⁶Ge respectively). For the ⁷⁶Ge/⁷⁴Ge isotope ratio, the relative standard deviation (RSD) is about 0.2–0.3%, based on the analyses of six samples.