Exhibit Hall | Forum 4
Purpose: The University and INFN Torino are studying thin silicon sensors and associated readout electronics for electron beam monitoring in high dose-rate regimes.
Methods: Inversely polarized thin silicon sensors, segmented in strips, are readout by a TERA08 chip, originally developed to readout gas monitors in charged particle therapy. One strip signal is split into 64 chip channels, whose counts gave the measured current. First tests were performed with electrons from an Elekta SL18 LINAC, entirely dedicated to research, which will undergo an upgrade to produce high dose-rate electron beams (~1 Gy/μs pulse) in the next months. Varying beam energies (4-10 MeV), distance to the source, sensor position in the beam field and dose-rates in the conventional range, the performance of sensor and readout in measuring the beam flux are being evaluated.
Results: Preliminary tests with electrons of 4, 6, 10 MeV up to 8 cGy/s conventional dose-rate confirmed the reproducibility of the system and the possibility to study beam profile and flatness. The present configuration of TERA08 (current to frequency converter with a charge quantum of 200 fC and a maximum output frequency of 20 MHz/channel) can sustain up to 256 μA instantaneous current in the pulse and is expected to be linear up to ten kGy/s dose-rate. The measured current is in agreement with the simulations of 6 MeV electrons interacting with thin silicon sensors (2.2 mm² x 45 μm thickness), resulting in instantaneous currents of few mA for 10⁵ Gy/s instantaneous dose-rates. An accurate calibration of the beam and the upgrade of the LINAC is ongoing.
Conclusion: The preliminary tests demonstrated the capability of silicon sensors with reduced active area and thickness and a TERA08 chip to measure the flux of electron beams in conventional dose-rates and promise to withstand dose-rates approaching FLASH ones.