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A big effort is addressed on developing alternative detectors able to maintain a linear response  at ultra-high dose-rate (UHDR), as ionization chambers suffer of ion recombination effects. Moreover, in the perspective of a clinical translation, QA measurements under the FLASH conditions imply the delivery of a huge amount of total dose per day, leading  to significant radioprotection issues, especially if beam profiles are scanned with a single point like detector. In this framework, the use of high radiation hard silicon carbide (SiC) detectors for the beam dosimetry and online monitoring of UHDR beams has been experimentally investigated in the perspective to design and develop a 2D SiC array allowing the measurement of the transversal beam profiles on a single shot basis.

A collaboration involving the INFN Catania Division and the start-up ST-Lab (Catania) has been established for developing a new generation of SiC detectors of different thicknesses (0.2- 20 um thick) and areas (1-10 mm2), including a never explored configuration based on ultra-thin “free standing membranes” where the bulk substrate is removed. The response of the SiC detectors, was studied with UHDR electron beams using the SIT Sordina ElectronFLASH accelerator available at the Centro Pisano for Flash Radio Therapy (CPFR) in Pisa, Italy. The measurements were carried out placing the different types of SiC detectors in air at the position of 9 MeV build-up (13 mm water equivalent depth) and measuring the charge collected by the SiC detectors with a Keithley 6517A electrometer coupled with an external RC circuit (R=2KΩ , C=1uF) needed to avoid saturation of the electrometer due to the extremely high peak current (up to 100’s of mA). Doses per pulse (DPP) ranging from few cGy up to 5 Gy were delivered on a pulse duration ranging from 1 us up to 4 us (up to 1.2 MGy/s  instantaneous dose rate).

Figure 1 (left) shows an optimal linearity (R2=0.999) of the SiC detector (5x5 mm2 and 10x10 mm2, 10 um thick) response as a function of the DPP. Alanine detectors were employed as a dose rate independent reference for the measurement of the delivered dose. Pulse shape time measurements at high time resolution (ns) were also performed (Figure 1, right), by connecting the detectors to a fast oscilloscope showing the high sensitivity of such detectors to the eventual intra-pulse small variations of the instantaneous dose rate which is one of the crucial parameters for the preclinical investigations of the FLASH effect. 

The results clearly demonstrated the dose-rate independence of  newly developed SiC detectors at FLASH regime and their capability of providing the intra-pulse real-time monitoring of the instantaneous dose rate  at high time resolution. Moreover, both large area SiC sensors and 2D configurations with high spatial resolution can be easily realized representing a unique a promising perspective for the QA and dosimetry measurements of UHDR beams.