Characteristics of Coaxial Ge(Li) Detectors through Warm-Up and Re-Drift Cycles

Studies have been made of several cylindrical coaxial Ge(Li) detectors through various cycles of warming to room temperature and subsequent 'cleanup' redrift - all in high vacuum. Conventional double-openend detectors with an n+-layer on the outside and a p-type core were used. Using the gamma-ray scanning technique it was observed that (1) When not fully cleaned up (capacitance decreasing with increasing voltage) the i-layer thickness increased from the n-layer towards the p-core as voltage was increased. (2) After a warm-up period, part of the i-layer nearest the core was lost with a reduction in efficiency (18% at 500V for one detector after an 8 hour warmup period). (3) Cleanup re-drift following a warm-up period restored the original characteristics but the cleanup time varied with the crystal from which the detector was made.