A single ion discriminator ASIC prototype for particle therapy applications

In the framework of the development of future advanced treatment modalities in charged particle therapy, the use of silicon sensors is an appealing alternative to gas ionization chambers commonly used for beam monitoring. A prototype of a device, based on Low-Gain Avalanche Diode (LGAD) sensors with 50 μm thickness, is being developed to discriminate and count single beam particles. This paper describes the design and characterization of ABACUS, an innovative multi-channel ASIC prototype for LGAD readout, based on a fast amplifier with self-reset capabilities. The design goals aim at detecting charge pulses in a wide range, from 4 fC to 150 fC, up to 70 MHz instantaneous rates, with a dead time of about 10 ns or less and efficiency larger than 98%. The characterization results indicate that even at the lowest input charge the signal-to-noise ratio is 15, high enough to keep full efficiency and preventing fake counts from the electronics noise. The dead time was found to be in the range between 5 ns and 10 ns, allowing to reach a full counting efficiency up to instantaneous rates of 70 MHz or larger, depending on the input charge.