Determination of homogeneity of the top surface deadlayer in an old HPGe detector

A collimated source of 241Am was scanned over the endcap of a 21 year old coaxial HPGe-detector that had spent about 75% of its life at room temperature (and the remaining time at 77 K). The detector response was recorded and used as a measure of the relative thickness of the top deadlayer. This thickness was not homogeneous and was thicker near to the outer surface of the crystal compared to the centre, which could be a result of increased diffusion of Li atoms during times the detector was kept at room temperature. The results were compared with two newer HPGe-detectors that proved to have homogeneous top deadlayers. •The top deadlayer of three HPGe-detectors were investigated.•One detector had been kept at room temperature for about 15 years.•The top deadlayer of this detector exhibited a heterogeneous structure.•The strange structure is presumably due to diffusion of Li-atoms.