Development and characterization of a 144-channel proton counter for particle therapy applications.

A prototype of an innovative beam monitor for particle therapy was developed by University and INFN of Torino, in order to count single protons up to a fluence rate of $10^{8} p/(cm^{2}s)$ in the clinical energy range (60-230 MeV). The designed detector is based on silicon sensors which show a better sensitivity and speed with respect to the state-of-the-art gas ionization chambers. The sensitive area is $2.6 \times 2.6 cm^{2}$, enough to cover the whole area of fix pencil beams, characterized by a FWHM of about 1 cm at the isocenter. The sensor is a $50 \mu m$ thick Low Gain Avalanche Diode segmented in 146 strips with $180 \mu m$ pitch. The readout frontend is based on 6 custom 24-channel ASICs, named ABACUS, able to discriminate proton signals in a wide charge range (3-150 fC) with a maximum dead time of about 10 ns. ABACUS digital outputs are sent to 3 Kintex7 FPGA boards for the counting operations. A LabVIEW program reads counters on the FPGAs, displays the counting rate and saves data for the offline analysis. The results of the proton counter characterization, performed both in laboratory and with proton beams, will be presented.