SEM Characterization of a Silicon Drift Detector for Electron Spectroscopy

Silicon Drift Detectors, widely employed in X-ray spectroscopy for high-resolution and high-count-rate applications, have found their application also in the β-decay spectroscopy measurements. The detection of electrons, in place of photons, yields to a different response of the detector. Electrons are absorbed in the very superficial layer of the SDD, where the quantum efficiency is not unitary. A novel SDD-based detector system is being developed in the context of the TRISTAN (Tritium Investigation on STerile to Active Neutrino mixing) project which searches for the presence of a keV-scale Sterile Neutrino by the investigation of the tritium β-decay spectrum. A detailed model of the SDD response is required for this specific application. This paper presents the experimental characterization of a single SDD pixel in a Scanning Electron Microscope (SEM) used as a mono-energetic electron source. The experimental data is then compared with Geant4 Monte Carlo simulations computing the interaction between the electrons and the detector's volume. The free parameters, defining the quantum efficiency profile of the entrance window model are then optimized to the values minimizing the difference between the real and the simulated spectra.