Design Of Anti-coincidence ? Spectrometer Based On FPGA

The influence of natural background and compton scattering in?-radiation measurement makes it difficult to detect low activity nuclides,so the anti-coincidence measurement method is introduced to improve it.In this design,?95×145×80mm annular NaI?Tl?crystal is used as anti-coincidence detector,and Binsong 3-inch NaI?Tl?detector is used as main detector.The main working principle of the system is as follows:the nuclear pulse signal at the output end of the main probe is processed by signal conditioning and ADC acquisition,and then it is processed with the peripheral anti-coincidence signal,and the identified signal is used to form?energy spectrum.When the main detector picks up the pulse signal and the ring detector has no signal,FPGA will keep the pulse signal of the main detector and process it with digital nuclear pulse signal to get the energy spectrum data.In hardware,this paper mainly introduces the design of hardware circuit with FPGA as the core,and introduces circuit design,including impedance matching circuit,program control gain circuit,amplifying and filtering circuit,high-speed ADC acquisition circuit,anti-conforming plastic circuit,FPGA digital signal processing circuit and USB data transmission circuit.The design of FPGA internal hardware design,mainly including digital clock module,nuclear signal acquisition and storage module,anti-coincidence discrimination module,trapezoid forming module,energy spectrum forming and USB data transmission module.The experimental results show that the anti-coincidence measurement system designed in this paper runs stably and can achieve the expected anti-coincidence effect.Through the analysis and comparison of the Geant4 simulated background data and the actual background data measured by spectrometer,it is found that the spectrometer measurement has good consistency with the simulated data,and the anti-coincidence measurement has a good suppression effect on the low energy background.Through the ¹³⁷Cs point source test,it is verified that the anti-coincidence measurement system not only has a certain inhibitory effect on the background,but also has a good Compton inhibition ability.