FPGA based signal processor for nuclear measurements

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Supervisor:
Szántó Péter
Department of Measurement and Information Systems

The purpose of my thesis was to develop a measuring system for a nuclear de-tector. Each hardver componenets were prvovided by developer boards. A Zynq-7000 System on Chip which includes two Cortex-A9 processors and FPGA within a one chip was used for the implementation. It integrates the software programmability of Cortec processors and the hardvare programmability of FPGAs.

After giving an overview on the basis of nuclear measurement technology both for analog and digital systems, I briefly discuss the theoretical background of our analysis. Then I describe the scintillation crystal detectors which were used to measure the radioactivity. The output of the detectors is a double-exponential time constant sig-nal whose amplitude is propotional to the detected particle’s energy and the rising time constant is typical to the source of radiation, so we can separate various types of radiati-on. To measure these signals precisely, I implemented trapez-filter in the FPGA logic. As a result of the measurement, a gamma spectrum is produced, which is typical to a given radioactive isotopes. If more than one isotopes were measured at the same time their spectrums overlapped. In order to identify the original isotopes and estimate their intensities I used response matrix deconvolution method. According to the method the problem can be reduced to solve an ill-posed linear equation system with iterative loss minimization. To optimise the runtime of the deconvolution I used SIMD library and implemented a hardware acceleration core in the FPGA for matrix multiplication which was designed in Vivado HLS.

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