Absolute isotopic composition and atomic weight of germanium

Gravimetric synthetic mixtures prepared from highly enriched isotopes of ge rmanium in the form of oxides of well defined purity were used to calibrate a thermal ionization mass spectrometer. Measurements on natural germanium samples yielded an absolute isotopic composition of 20.38(10) at. % Ge-70, 27.34(9) at. % Ge-72, 7.75(5) at. % Ge-73, 36.71(9) at. % Ge-74, and 7.82(4 ) at. % Ge-76, and the atomic weight of germanium as 72.639(7) both with an uncertainty given on the basis of 95% confidence limit. No isotopic fracti onation was found in terrestrial normal germanium materials. (Int J Mass Sp ectrom 189 (1999) 205-211) (C) 1999 Elsevier Science B.V.