| Ionization chambers are often applied in nuclear physics experiments for the identification of charged particles,and energy resolution is an important parameter to characterize their performance.In general,the factors affecting the energy resolution of gas detectors are mainly the statistical fluctuations of the ionization process,the electronic noise of the detector output loop,etc.The statistical fluctuations of the ionization process of the incident particles determines the intrinsic energy resolution of the detector,related to the measured particles and the working medium.Therefore,the energy resolution is often improved by improving the signal-to-noise ratio of the detection system.The noise of the system mainly originates from the detector and the preamplifier.The signal-to-noise ratio can be improved by using a preamplifier with lower electrical noise;and by optimizing the detector design to reduce its output capacitance,but this method is more demanding in terms of electronics.The energy resolution of the ionization chamber needs to be further improved for the detection of particles with deposition energies of several hundred ke V due to the influence of the electronics noise.This paper focuses on improving the energy resolution of the ionization chamber through both detector structure optimization and waveform processing algorithms.The detector in this paper is improved on the basis of the Frisch-grid ionization chamber.The multi-wire proportional chamber is added to the signal readout end to improve the energy resolution of the detector for lower energy deposited particles by enhancing the signal amplitude and increasing the signal-to-noise ratio through the avalanche amplification of electrons near the anode.The optimal operating voltage of the detector is related to the energy of deposition of the incident particles in the drift region;the lower the deposition energy,the higher the corresponding optimal operating voltage and the higher the gain of the detector.The energy resolution of alpha particles of 5.486 Me V can reach about 1.45%.The analog circuits were digitized using four different methods.A detailed simulation of the pulse height loss due to capacitive discharge in the detector output loop was performed,and the signal height loss due to capacitive discharge is not negligible when the duration of the current signal is not negligible with respect to the time constant of the detector output loop(about 2.5% amplitude loss when the time constant of the detector output loop is25 times the duration of the current).The correction of the amplitude of the single exponential decay signal and quasi-Gaussian filtering and shaping were realized on the basis of the digital circuit.The digital waveform processing algorithm is verified with experimental data obtained by oscilloscope sampling.Compared with the analog circuit,the digital waveform processing method can improve the signal-to-noise ratio and the energy resolution of the detector(from 10% to about 5%). |
