HIGH-PURITY ISOTOPICALLY ENRICHED GE-70 AND GE-74 SINGLE-CRYSTALS - ISOTOPE-SEPARATION, GROWTH, AND PROPERTIES

Ge-70 and Ge-74 isotopes were successfully separated from natural Ge a nd zone purified. Several highly enriched, high purity Ge-70 and Ge-74 single crystals were grown by the vertical Bridgman method. The growt h system was designed for reliable growth of low dislocation density, high purity Ge single crystals of very small weight (approximately 4 g ). A Ge-70 and a Ge-74 crystal were selected for complete characteriza tion. In spite of the large surface to volume ratio of these ingots, b oth Ge-70 and Ge-74 crystals contain low electrically active chemical net-impurity concentrations of approximately 2 X 10(12) cm-3, which is two orders of magnitude better than that of Ge-71 crystals previously grown by two different groups.1,2 Isotopic enrichment of the Ge-70 an d the Ge-74 crystals is 96.3% and 96.8%, respectively. The residual do nors and acceptors present in both crystals were identified as phospho rus and copper, respectively. In addition, less than 10(11) cm-3 galli um, aluminum, and indium were found in the Ge-70 crystal.