FPGA-based simulator of HPGe gamma-ray spectra using RFID tokens as sources for educational and calibration applications

The use of ionizing radiation sources spans a wide range of applications; however, it inherently entails significant risks. Consequently, gamma-ray spectroscopy has become an essential tool for radionuclide identification, with high-purity germanium (HPGe) detectors representing one of the most suitable options due to their superior energy resolution. Nevertheless, their implementation in educational, training, and laboratory settings faces several limitations, including high cost, the requirement for cryogenic cooling, and the strict regulations governing the handling of radioactive sources. This work presents the development of a high-purity germanium detector simulator embedded in an FPGA. The system was designed not only to reproduce the nuclear pulses that compose the spectra of various radionuclide sources, but also to control the number of simulated pulses as a function of the type of source employed (Cs-137, Co-60, Ba-133, Eu-152, Na-22) and its distance from the detector. In addition, in the absence of a placed source, the simulator generates pulses corresponding to background radiation. The results demonstrated a strong similarity between the simulated and experimental spectra. Furthermore, three calibration procedures, based on energy, time, and distance, yielded correlation coefficients close to unity. The FPGA-based simulator thus constitutes a viable and cost-effective alternative for teaching gamma-ray spectroscopy, effectively overcoming the limitations of purely computational simulations. Its implementation enables the reproduction of calibration exercises, spectrum analysis, and demonstrations of fundamental physical phenomena without the need for real radioactive sources, thereby contributing to training in nuclear instrumentation and the development of accessible educational resources.