A FPGA-based software for microdosimetric data processing

The tissue equivalent proportional counter (TEPC) is the most accurate device for measuring microdosimetric properties of particle beams. Since microdosimetric quantities span over several decades, the electronic and acquisition chain should meet specific requirements. In order to cover the wide dynamic range of the signals generated by the TEPC, the output signal from the preamplifier is fed in parallel to three linear amplifiers which shape and amplify the signal with different gains. Very low-energy deposition events are filtered in the high-gain stage, and high-energy deposition events are processed in the low-gain stage. A new system with high acquisition performance and compact hardware was developed for this purpose. The analog-to-digital conversion is performed by a commercial acquisition system that includes a FPGA. Thanks to the FPGA a parallel high-speed acquisition on three channels can be performed. The software merges signals together from the three electronic chains and computes a real time microdosimetric spectrum giving a prompt information about the irradiation field. This acquisition system, which performs analog-to-digital conversion and signal processing at a sampling rate up to 15 MS/s, was tested by irradiating a TEPC with an Am-Be fast neutron field, an intense quasi-monoenergetic neutron beam and a 62 MeV/u helium ion beam.