Determination of dead-layer variation in HPGe detectors

•We performed a top dead-layer topography of two HPGe detectors.•We identified a non-uniform dead-layer thickness along the surface of one of them.•We built a Monte Carlo model able to reproduce the measurements results.•We estimated an effect on the activity calculation for low energy γ-ray emitters of ~50%.

The dead-layer uniformity of the top surface of two high purity germanium detectors has been studied using a novel automated scanning set-up that allows a fine-grained topography of a detector's top and lateral surfaces. Comparisons between measurements and Monte Carlo simulations allowed implementation of a dead-layer variation into the detector model, which reproduces the measurements results. The effect of the non-uniform dead-layer on activity determinations based on low-energy γ-rays (i.e. below ~100 keV) has been determined to be of the order of 10% or more.