Charge collection mapping of a novel ultra-thin silicon strip detector for hadrontherapy beam monitoring

In precise hadrontherapy treatments, the particle beam must be monitored in real time without being degraded. Silicon strip detectors have been fabricated over an area as large as 4.5×4.5 cm2 with ultra low thickness of 20 μ m . These offer the following considerable advantages: significantly reduced beam scattering, higher radiation hardness which leads to improved detector lifetime, and much better collection efficiency. In a previous work, the novel sensor has been described and a global macroscopic dosimetry characterization has been proposed. This provides practical information for the detector daily use but not about the local microscopic knowledge of the sensor. This work therefore presents a micrometric-accuracy charge-collection characterization of this new generation of ultra-thin silicon strip detectors. This goal is reached thanks to a 1060 nm-wavelength micrometric-sized laser that can be positioned relatively to the sensor with a submicron precision for the three different axes. This study gives a much better knowledge of the inefficient areas of the sensor and allows therefore optimization for future designs.