A two-in-one gamma-ray spectrometer and random pulse generator based on FPGA

Abstract

The gamma-ray spectrometer (GRS) is a powerful tool to acquire energy spectra. For the traditional analog GRS based on commercial modules and the digital GRS based on ultra-fast digitization, it is difficult to meet the requirements of high resolution and high throughput simultaneously, and the energy spectrum cannot be obtained in real-time. Besides, energy spectra experiments require the use of radioactive sources. Prolonged exposure to the sources will harm the human body. In this paper, we introduce a digital GRS based on an ordinary analog-to-digital converter (ADC). To avoid human body exposure to radiation in spectra tests, we integrated a digital-to-analog converter based random pulse generator (RPG) on the board to simulate the real nuclear pulses. The algorithms were accomplished by a field-programmable gate array (FPGA). The electronic test results show that the effective number of bits of ADC reaches 11.78 bit, and the spectrometer works well when the average frequency of the input pulse is under 3 MHz. The energy resolution of the 511 keV photopeak reaches 4.05% when using LaBr3:5% Ce3+ scintillator and 22Na source. The energy spectrum is obtained through FPGA in real-time and can be delivered to the personal computer via Ethernet or displayed on the local screen. The RPG can generate simulated nuclear pulses with Gaussian distributed energy. The mean and sigma of the Gaussian curve and the event rate of output pulses can be configured.