Development Of High Purity And Digital Dual Channel Pulse Amplitude Analyzer

The high-purity germanium detector is a commonly used nuclear radiation detector that converts the detected radiation into an electrical pulse signal.Although the detection efficiency is not high,but it has a high energy resolution and plays an important role in X-ray and gamma ray detection.The pulse amplitude analyzer collects and extracts the pulse amplitude and arrival time of the pulse signal output by the detector,which is an indispensable tool in the measurement of nuclear radiation energy spectrum.The traditional two-channel pulse amplitude analyzer is limited by the resolution and conversion speed of the ADC.The analog signal is used to shape and amplify the pulse signal,which leads to the circuit noise of the pulse amplitude analyzer,low pulse count rate,slow response time,etc.Disadvantages.With the continuous improvement of the performance of electronic devices,this paper designs an all-digital dual-channel pulse amplitude analyzer,which adopts high-speed and high-precision ADC technology,avoids the analog signal shaping process,reduces the circuit noise,and improves the pulse count rate.Small system dead time.For each channel,this paper designs two pulse shaping algorithms.The slow pulse shaping includes trapezoidal filtering,baseline recovery,and stack identification to extract the pulse amplitude;rapid pulse shaping includes trapezoidal filtering and threshold discrimination to obtain the arrival time of the pulse.In terms of interaction,Gigabit Ethernet port and energy spectrum analysis software are used for data transmission.This research started from the project,fully researched the research status at home and abroad and focused on the nuclear measurement field CAEN company’s products,experienced the measurement program design,simulation verification,system design,parameter debugging,system function and stability testing process.Finally,an all-digital dual-channel pulse amplitude analyzer with high energy resolution and high stability has been developed,which can fully exploit the advantages of high-purity germanium detectors.The main work of this paper includes:1.High-purity germanium detector readout circuit power supply design.A low-noise±24V and±12V power supply is designed to power the detector readout circuitry with 5mV supply ripple noise.2.Design of analog pulse signal conditioning circuit.Including:front-end program-controlled amplifier circuit,programmable gain adjustment circuit and ADC differential drive circuit,which realizes amplification and conversion of analog pulse signal into differential signal.The pulse gain can be flexibly adjusted and translated by software settings.3.Design of a fully differential analog-to-digital conversion circuit.Using TI’s105M,14Bit analog-to-digital conversion chip ADS5424,the speed and accuracy of the system are guaranteed.4.FPGA-based pulse signal processing scheme.The system adopts FPGA processing architecture,which has simple structure and strong programmability,and mainly implements algorithms such as pulse amplitude extraction and pulse arrival time.5.Gigabit network high speed data transmission circuit design.In order to ensure the speed of spectrum data transmission and interaction,the Ethernet physical layer chip KSZ902RN is used to achieve a transmission speed of 125 MB/s.The chip communicates with the FPGA through the RGMII interface and transmits using the UDP protocol.The system was tested:the analog circuit bandwidth was 20 MHz and the gain fluctuated by 0.1.The linearity of the system is 0.9979 and the maximum pulse count rate is 800Kcpc.For the energy spectrum measurement,the energy peak resolution of the two channels is 0.24%and 0.25%(²²Na radioactive source).The positron is in accordance with the Doppler broadening spectrum measurement,and the two-dimensional conforms to the normal broadening of the spectrum,which is in accordance with the peak-to-valley ratio of 10⁴:1.The stability is measured,and the peak position of the energy spectrum is measured continuously for 8 hours.The peak position is not offset,and the stability of the system is good.