Comparing proton and neutron induced SEU cross section in FPGA

Single event upsets (SEU) are induced by an electric charge deposited in the material of the chip. The origin of the charge can be either from outside of the chip or it can be generated inside as a result of a nuclear reaction. We have measured the cross section of SEUs in FPGA using protons (directly ionizing particles) and neutrons (indirectly ionizing particles). Used energies up to 34 MeV are in the range, where the differences in the proton's ionizing power are most significant thanks to the Bragg peak. Measurements have shown, that the direct ionization is not the dominant effect causing SEU.