Dead layer characterization of a well-type HPGe detector by iterative Geant4 Monte Carlo adjustment: from constant to variable thickness profiles

Accurate modelling of the dead layer is essential for reliable Monte Carlo efficiency calculations of HPGe detectors, in particular at low γ energies. In this work, an iterative Geant4 approach was applied to characterize the effective dead-layer distribution of a well-type HPGe detector using experimental efficiencies from a 137 Cs point source. A constant-thickness model was first adjusted, followed by a spatially variable model in which the inner, outer, and top dead layers were segmented and fitted according to source position. The variable model improved the agreement at 32 keV, reducing the maximum simulation-to-experiment deviation from 15.4% to 3.2%. At 662 keV, both models produced comparable agreement, indicating a lower sensitivity to local dead-layer variations. The results demonstrate the importance of accounting for spatial dead-layer variations at the well HPGe response in low-energy.