RESUMO
BACKGROUND: The extremely fast delivery of doses with ultra high dose rate (UHDR) beams necessitates the investigation of novel approaches for real-time dosimetry and beam monitoring. This aspect is fundamental in the perspective of the clinical application of FLASH radiotherapy (FLASH-RT), as conventional dosimeters tend to saturate at such extreme dose rates. PURPOSE: This study aims to experimentally characterize newly developed silicon carbide (SiC) detectors of various active volumes at UHDRs and systematically assesses their response to establish their suitability for dosimetry in FLASH-RT. METHODS: SiC PiN junction detectors, recently realized and provided by STLab company, with different active areas (ranging from 4.5 to 10 mm2) and thicknesses (10-20 µm), were irradiated using 9 MeV UHDR pulsed electron beams accelerated by the ElectronFLASH linac at the Centro Pisano for FLASH Radiotherapy (CPFR). The linearity of the SiC response as a function of the delivered dose per pulse (DPP), which in turn corresponds to a specific instantaneous dose rate, was studied under various experimental conditions by measuring the produced charge within the SiC active layer with an electrometer. Due to the extremely high peak currents, an external customized electronic RC circuit was built and used in conjunction with the electrometer to avoid saturation. RESULTS: The study revealed a linear response for the different SiC detectors employed up to 21 Gy/pulse for SiC detectors with 4.5 mm2/10 µm active area and thickness. These values correspond to a maximum instantaneous dose rate of 5.5 MGy/s and are indicative of the maximum achievable monitored DPP and instantaneous dose rate of the linac used during the measurements. CONCLUSIONS: The results clearly demonstrate that the developed devices exhibit a dose-rate independent response even under extreme instantaneous dose rates and dose per pulse values. A systematic study of the SiC response was also performed as a function of the applied voltage bias, demonstrating the reliability of these dosimeters with UHDR also without any applied voltage. This demonstrates the great potential of SiC detectors for accurate dosimetry in the context of FLASH-RT.
RESUMO
In recent times, ion implantation has received increasing interest for novel applications related to deterministic material doping on the nanoscale, primarily for the fabrication of solid-state quantum devices. For such applications, precise information concerning the number of implanted ions and their final position within the implanted sample is crucial. In this work, we present an innovative method for the detection of single ions of MeV energy by using a sub-micrometer ultra-thin silicon carbide sensor operated as an in-beam counter of transmitted ions. The SiC sensor signals, when compared to a Passivated Implanted Planar Silicon detector signal, exhibited a 96.5% ion-detection confidence, demonstrating that the membrane sensors can be utilized for high-fidelity ion counting. Furthermore, we assessed the angular straggling of transmitted ions due to the interaction with the SiC sensor, employing the scanning knife-edge method of a focused ion microbeam. The lateral dimension of the ion beam with and without the membrane sensor was compared to the SRIM calculations. The results were used to discuss the potential of such experimental geometry in deterministic ion-implantation schemes as well as other applications.
