| The fast neutrons and associated particles which are produced by the deuteriumtritium fusion reaction have temporal and spatial correlations.This characteristic can be used to carry out magnetic confinement fusion diagnosis,neutron source intensity measurement and neutron activated element imaging analysis.The neutron activated element analysis method based on associated particle imaging can improve the signalto-noise ratio of prompt gamma energy spectrum,reduce the amount of shielding materials,and achieve three-dimensional elements distribution.It has application potential in fields such as deep space exploration and planetary geological exploration.However,the currently commonly used scintillator-based associated particle detectors have complex photoelectric conversion structures,large volumes and weights,while silicon detectors have poor high-temperature resistance and radiation resistance.The existed associated particle detection technology cannot meet the operational requirements with high environmental adaptability,long life,and high neutrons intensity.Therefore,it is necessary to develop new high-temperature resistant,radiation resistant and compact assoicated particle detection technology.In response to the above problems,this thesis proposes a high-temperatureresistant associated particle measurement scheme that uses a SiC detector as the associated particle detector and SiC-JFET as the input transistor of the preamplifier.This study carried out simulation and experimental preparation of SiC pixel detector,tested its electrical characteristics and particle detection performance at high temperatures,developed an associated particle imaging element analysis system based on SiC detectors.The high temperature characteristics and noise performance of the SiC-JFET was studied when used in the input stage of a charge-sensitive preamplifier.Finally,the experimental preparation and performance testing of SiC-JFET was carried out.The main contents and results of this thesis are as follows:(1)The simulation,preparation and testing of pixel SiC detectors were conducted.The effect of the field plate on the electrical and signal characteristics of the detector was simulated and examined using the TCAD method.According to the simulation results,the field plate aids in lowering the peak electric field at the pixel’s edge,which can lower leakage current,but also distorts the output signal of the incident particle at the edge.A 3×3 pixel SiC detector with 2×2 mm2 pixels was produced.The detector bundled with a ceramic substrate and sintered nano-silver paste could withstand six hours of baking at 300℃.The pixel SiC detector exhibited a leakage current of less than 1μA and could operate steadily at 300℃.The particle detection experiment demonstrate that the packaged detector can output pulse signals steadily at 300℃ and has no loss in energy resolution below 150℃.(2)An associated SiC detector-based particle imaging system was built and tested.The SiC associated particle detectors have an average energy resolution of less than 6.8%for associated particles and less than 1.6%for Am-241 alpha particles.The measurements of the graphite sample demonstrated that the associated particle imaging system can precisely detect the 4.4 MeV prompt gamma ray from fast neutron excited carbon atoms with an energy resolution of less than 3%.The system’s inherent time resolution was less than 2 ns.The system’s spatial resolution in the direction of neutron flight was 10 cm,and it was able to discriminate between numerous samples that were dispersed randomly within the field of vision while also can given the sample’s three-dimensional elemental distribution.(3)The electrical characteristics of a small-signal SiC-JFET and its variation at high temperatures were studied.The noise contribution of SiC-JFET when used as the input transistor of charge-sensitive preamplifier and its sensitivity of the temperature was investigated.According to the TCAD simulation results,SiC-JFET has good high temperature stability and a broad operating temperature range.The transconductance change is less than 31%in the temperature range 25～250℃,and it has normal working ability at 400℃.The noise of SiC-JFET is always lower than that of Si-JFET with the same structure in the shaping time between 0.1～10 μs and temperature between 25～400℃.SiC JFETs have low noise at temperatures above 50℃ when connected with a small-capacitance SiC detector.When combined with a self-developed SiC pixel detector,SiC JFETs have the advantage of low noise at higher temperatures and a shorter shaping time.(4)The preparation and test of SiC-JFET were carried out,and the device preparation process and high-temperature performance test were discussed.At room temperature,the SiC-JFET’s measured transconductance is 0.35 mS,which was around 49%of the theoretical value.The pinch-off threshold voltage for the channel is-5.4 V,and saturation current is 0.78 mA.The crystal defects and significant drain-source series resistance are the main causes of the discrepancy between the measured value and the theoretical value.The transconductance of SiC-JFET is lowered by approximately 34%and the saturated drain current is reduced by approximately 36%from room temperature to 200℃,which is consistent with the simulation results.The gate leakage current density in the working state can reach 1 mA cm-2,but it only multiplies by 1.3 at 200℃,which shows that the noise change of SiC-JFET at high temperature is negligible.The process needs to be further optimized to reduce the gate leakage current at room temperature.To summarize,in this study,a technical solution based on SiC detector and SiCJFET was proposed to address the problem of high-temperature resistance of associted particle detection technology in deuterium-tritium fusion neutron source.The SiC pixel detector was simulated and experimentally prepared.An associated particle imaging system based on SiC detectors was developed and tested.The noise changes of semiconductor detector and front-end electronics at high temperature were comprehensively analyzed,and the electrical characteristics of high-temperature resistant SiC-JFET were simulated and studied,and experimental preparation and testing were carried out.The research results of this study provide a theoretical and experimental basis for the development of high temperature resistant associated particle detection technology,as well as the development of high temperature resistant front-end nuclear electronics special devices and circuits. |
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