Lithium Drift Rates and Oxygen Contamination in Germanium

The unpredictable variations in lithium drift rates of various commercially available germanium crystals have made the production of germanium gamma-ray detectors rather difficult. Some asreceived germanium ingots have shown diffusion constants D reduced by nearly three decades. Because drift time varies inversely with D, the time required to drift such germanium to make large-volume detectors can become too long to be practical. The drift rates and lithium precipitation kinetics of such germanium were investigated to determine if they were correlated. We have examined the lithium precipitation kinetics in 24 samples cut from 13 different germanium crystals covering a wide range of drift rates. These samples were cut from both zone-leveled and pulled crystals from three vendors.