Response modelling of a-Si:H detector read by TetrAMM picoammeter exposed to a clinical electron beam

The INFN HASPIDE project investigates hydrogenated amorphous silicon (a-Si:H) as an innovative detector technology for dosimetry in FLASH radiotherapy. Conventional dosimeters, such as ionization chambers, show non-linear behavior when exposed to ultra-high dose-per-pulse beams used in FLASH radiotherapy, where several Grays are delivered in microsecond pulses. Thanks to its radiation hardness, mechanical flexibility and compatibility with large-area deposition, a-Si:H is a promising material for in-vivo and surface dosimetry. This work presents the response of a thin a-Si:H detector exposed to a high-dose-per-pulse 10MeV electron beam, together with an analytical model used to describe the single-pulse dynamics and extract quantitative parameters. Measurements were performed at the University of Torino using a modified clinical LINAC operated in Ultra High Dose Rate regime, where the single-pulses satisfy the FLASH criteria. The a-Si:H detector, read out with a TetrAMM picoammeter (100kHz sampling frequency), resolves individual radiation pulses with high repeatability. Both pulse charge and peak current scale linearly with the applied electric field up to 6V (2.4 V/μm), beyond which the readout electronics saturates. The analytical model is validated through direct comparison with raw data, showing excellent agreement in extracted pulse parameters.