基于光电雪崩二极管的碘化铯能谱读出设计

发布时间：2018-04-04 15:23

本文选题：伽玛测井探头　切入点：雪崩光电二极管　出处：《成都理工大学》2015年硕士论文

【摘要】：随着化石燃料迅速消耗,石油勘探难度日益增大,勘探深度逐渐增加,井液温度和井压随之增高,且探管随之减小,对伽玛能谱测井提出了更高的要求。当前能谱测井仪的探测器主要采用NaI(T1)匹配光电倍增管(PMT)进行探测,其体积较大,对高能射线的探测效率较低,温度稳定性差,仪器分辨率较低,如北京环鼎公司研制的GST数字自然伽玛能谱测井仪,外径较大(约99mm),20℃时仪器分辨率差于12%,175℃时差于15%。为此设计高探测效率、高稳定性、高分辨率的小体积伽玛能谱测井探头具有重要意义。天然伽玛能谱测井是运用核物理学的方法,解决地球科学、环境科学等有关问题的主要手段之一。伽玛能谱测井中能谱仪性能的好坏主要取决于其探头的能量分辨率,灵敏度以及稳定性等因素。当前常用的伽玛能谱仪主要由伽玛辐射探测器、信号处理电路,数据采集器以及数据处理解释算法软件等组成。其中伽玛辐射探测器通常采用NaI(T1)等无机闪烁体与PMT及前放组成,结构上均采用主机和探头分离设计模式,在长期的使用中其表现有如下不足：首先,PMT工作电压为近千伏高压,功耗相对较大,在测井环境中易造成信号短路,若设计或使用不当,存在被电击的风险；其次,PMT为真空易碎器件,实际测井过程中常伴随剧烈震动,易使其损坏；最后,PMT体积相对较大,在小井眼探测领域选型困难。针对测井能谱仪在环境场所测量的实际要求,基于传统井能谱仪的不足,结合对当前市场中测井谱仪的调研,依托电子技术微型化的发展,本文提出了基于雪崩光电二极管(APD)的碘化铯CsI(T1)能谱设计方案。探头采用APD和CsI(T1)闪烁晶体组合方式,利用CsI(T1)闪烁晶体的能量灵敏度大、光产额高、对伽玛射线吸收系数大以及机械性能良好的优势,利用APD与CsI(TI)晶体良好的光谱匹配和光电转换特性以及APD较大内部增益等特点,对被测微弱核信号进行光电转换并放大。设计了低噪声低功耗电荷灵敏前置放大器,以提高系统信噪比和能谱仪的探测效率。利用信号处理电路降噪放大成形,采用高速模数转换器将信号离散化,以资源丰富的FPGA作为微处理器,实现数字多道脉冲幅度分析,主要包含基线估计与复位、计数率校正、脉冲幅度分析、脉冲抗堆积、脉冲波形甄别等功能,提高系统的稳定性和能谱仪的能量分辨率。最后将测量结果传入上位机软件进行详细的测试和分析。经过为期一年多的设计和开发工作,取得了以下成果：1、采用Hammatsu公司的雪崩光电二极管(S8664-1010)与碘化铯CsI(T1)(体积：10mm×10mm×10mm)闪烁晶体组合作为自然伽玛能谱测井仪的探测器,采用硅油进行光学耦合,使Si APD与碘化铯CsI(T1)闪烁晶体在光谱上达到最佳匹配,以保证较高的光学探测效率；2、基于交流耦合—阻容反馈式折叠型的经典结构,设计了低噪声低功耗的电荷灵敏前置放大器,零电容噪声是2599e-,噪声斜率为24e-/pF；3、设计了核信号处理电路、高速模数转换器ADC以及以FPGA为主体的数字脉冲信号处理模块(DMCA);4、搭建实验平台,对仪器在不同偏压、不同温度、不同放射源条件下的出谱情况进行了详细的测试。测试结果如下：1、首先对’37Cs进行不同偏压测试,结果表明偏压增大,探测器输出信号幅值显著增加,且能量分辨率明显变好,370V时,能量分辨率最佳,可达4.98%；2、设置最佳偏压370V,在-20℃～40℃温度范围内以20℃为间隔递增测量137Cs,在-20℃时,能量分辨率最好(约4.77%),随温度升高而变差,40℃时为5.38%,仍然远高于当前测井谱仪能量分辨率,如530SGS型自然伽玛能谱探头,其能量分辨率仅为8.958%；3、分别测量不同放射源60Co、152Eu、226Ra释放的伽玛射线时,其能量特征峰均能被清晰识别。整个系统测试情况充分验证了CsI(Tl)+SiAPD探测组件作为深部伽玛能谱测井探头的合理性与优越性。
[Abstract]:With the rapid consumption of fossil fuels, increasing the difficulty of petroleum exploration, the exploration depth increases gradually, temperature and well liquid pressure increased, and the probe decreases, on gamma ray spectrolog put forward higher requirements. The current spectrum logging detector mainly uses NaI (T1), photomultiplier tube (PMT) detect the large volume, high energy ray detection efficiency of low temperature stability, low resolution, such as GST digital development of Beijing huanding natural gamma spectrum logging company, the larger outer diameter (about 99mm), at 20 C for 12% meter resolution, 175 C in 15%. this time the design of high detection efficiency, high stability, small volume, high resolution gamma energy spectrum logging probe has important significance. The natural gamma ray spectrometry logging method is used to solve the nuclear physics, earth science, one of the main means of issues related to environmental science. Gamma Mary can energy resolution spectrometer performance spectrum logging in mainly depends on the factors of the probe, sensitivity and stability. The current commonly used gamma spectrometer is mainly composed of a gamma radiation detector, signal processing circuit, data acquisition and data processing and interpretation algorithm software etc.. The gamma radiation detector usually adopts NaI (T1) inorganic scintillator and PMT and the composition, structure and adopts host probe separation design pattern, in the long-term use of its performance has the following disadvantages: first, the working voltage is nearly PMT kV high voltage, power consumption is relatively large, easy to cause the short circuit signal in well logging environment, if the design or improper use and there is the risk of electric shock; secondly, PMT vacuum fragile devices, severe vibration often associated with the actual logging process, easy to damage; finally, PMT relatively large volume in slim hole detection field selection Difficult. According to the logging spectrometer in the actual requirements of environment measurement, shortcomings of traditional wells spectrometer based on the combination of research in the current market logging spectrometer, relying on the development of miniaturized electronic technology, is proposed in this paper based on avalanche photodiode (APD) iodide (T1) spectra of cesium CsI design using APD and CsI program. The probe (T1) scintillation crystal combination, using CsI (T1) scintillation crystal energy sensitivity, high light yield, high absorption coefficient and good mechanical properties of the advantages of gamma rays, using APD and CsI (TI) spectra of crystal good matching and photoelectric conversion characteristics and APD the larger internal gain characteristics of photoelectric conversion and amplification of weak signal to be measured. Nuclear design of low power low noise charge sensitive preamplifier, in order to improve the SNR and spectrum detection efficiency. Using the signal processing circuit and noise amplification High speed analog-to-digital converter, the signal discretization, with FPGA rich as the microprocessor to realize digital multi-channel pulse height analysis, including baseline estimation and reduction, count rate correction analysis, pulse amplitude, pulse pile up, pulse shape discriminator function, improve the system stability and energy resolution of the spectrometer will last. The measurement results to the host computer software is tested and analyzed in detail. Through the design and development for more than a year of work, and achieved the following results: 1, the avalanche photodiode Hammatsu company (S8664-1010) and CSI CsI (T1) (volume: 10mm * 10mm * 10mm) detector as a combination of natural gamma scintillation crystals spectrum logging, using silicone and optically coupled to the Si APD CsI (T1) and cesium iodide scintillation crystal to achieve the best match in the spectrum, in order to ensure the optical high detection efficiency; 2, The classic structure of AC coupled resistive and capacitive feedback type folding type based on the design of low power low noise charge sensitive preamplifier, zero capacitor noise is 2599e- noise, the slope is 24e-/pF; 3, design the nuclear signal processing circuit, high-speed ADC ADC and with FPGA as the main body of digital pulse signal processing module (DMCA); 4, build the experimental platform, the instrument in different voltage, different temperature, different sources under the conditions of the spectral detail test. The test results are as follows: 1, the first test of different bias' 37Cs, results show that the voltage increases, the amplitude of the output signal of the detector was significantly increased, and the energy resolution is much better 370V, when the best energy resolution, up to 4.98%; 2, setting the optimum bias voltage of 370V, in the -20 to 40 DEG C temperature range to 20 DEG C for increasing interval measurement 137Cs, at -20 DEG C, the best energy resolution (about 4.77 %) but decreased, with the increase of temperature at 40 DEG C for 5.38%, still much higher than the current log spectrum energy resolution, such as natural gamma energy spectrum 530SGS probe, the energy resolution is only 8.958%; 3 were measured in different sources of 60Co, 152Eu, Gamma Ray released by 226Ra, the characteristic peak energy can be clearly identified. The test cases CsI (Tl) has verified the rationality and superiority of +SiAPD detection module for deep gamma spectrum logging probe.

【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P631.817

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