Evidence for low-energy electron contribution to vacuum Compton detector intrinsic sensitivity under bias fields

Abstract

Intrinsic sensitivity is a key parameter for vacuum Compton detectors (VCDs), enabling the quantitative analysis of pulsed γ-radiation fields. Since VCDs are insensitive to the emitted electron energy, traditional calibration of intrinsic sensitivity has generally neglected the contribution of low-energy electrons. In this work, a zero-bias Monte Carlo (MC) simulation with and without low-energy electron transport using the Geant4 toolkit gave nearly the same net yield and intrinsic sensitivity. To test whether an applied electric field can still enhance the detector response beyond this zero-bias baseline, an experimental VCD system incorporating bias electrodes was designed. By applying an electric field across the emitter, the signal was enhanced by over 10% under 60Co irradiation, with Al reaching a maximum increase of 15%. Further analysis of the derivative of the signal-voltage curve revealed that this enhancement mainly originated from electrons below 20 eV, which is consistent with the energy range of true secondary electrons. When the vacuum bias field is included in the Monte Carlo calculation, the predicted sensitivity remains essentially unchanged relative to the zero-bias case. The measured gain is therefore attributed to near-surface processes that are not included in the present vacuum-transport framework. This study provides experimental evidence that low-energy secondary electrons can measurably enhance VCD intrinsic sensitivity under bias-assisted conditions, identifies a concrete modeling gap at the surface under bias, and suggests a practical route for sensitivity enhancement.