Improved Resolution Of ? Spectrometer At High Count Rates Based On FPGA

Currently,nuclear analysis method are widely used in the filed of industry,agriculture,environment,safety,medinine,archaeology,aerospace,energy and materialogy.Spectral acquisition and analysis techniques can accurately and quantitatively analyze target substances,and they are highly dependent on the acquisition of relevant high-resolution nuclear energy spectra.With the rapid improvement of digital signal processing technology,high speed and resolution ADC and high performance digital signal processing devices,the multi-channel pulse analysis technique has gradually developed toward digital signal processing,and digital nuclear spectrum acquisition has become the mainstream today.The dissertation mainly focuses on the work of NaI?Tl?scintillator detectors at high counting rate environments.And how to improve the resolution of digital gamma spectrometers as far as possible is concerned.First of all,theoretical analysis and experimental testing demonstrate the feasibility of using the area analysis method to obtain the nuclear energy spectrum for the nuclear pulse output by the emitter follower,and also prove that the method has significant effect to suppress the signal noise compared to the traditional amplitude analysis method.Afterwards,a novel method of pulse width analysis method was applied to real-time digital discriminate and reject the pile-up nuclear pulse at high counting rate.The method can recognize the accumulation of front and rear edge of the pulse in the real time and improve the status of unidentifiable pulse front accumulation.Finally,method of obtaining baseline on dynamic real-time average method was used to reduce the influence of baseline drift on energy spectrum acquisition system.Experimentally,signal source of imitating nuclear radiation pulse was generated through combining the arbitrary function generator of Tektronix AFG3102 with the ArbExpress software.The influence of pulse signal noise,amplitude and sampling points on area analysis and amplitude analysis method was tested and analyzed.In the meantime,under the condition of radioactive source with counting rate of approximately 20000 s^-1,the pulse pile-up rejection and baseline recovery algorithms were tested using area analysis and amplitude analysis methods.And The gamma spectrum resolution results obtained by these two methods were compared and analyzed.Finally,the effects of sampling points on the gamma spectral resolution were experimentally analyzed in terms of changing the signal processing clock frequency at high count rates and adjusting the pulse width at low counting rates.