李太楓臺灣大學：物理研究所蕭凱譽Shiao, Kai-YuKai-YuShiao2007-11-262018-06-282007-11-262018-06-282006http://ntur.lib.ntu.edu.tw//handle/246246/54633為了研究由美國太空總署從外太空帶回來的彗星粉塵樣本之同位素豐度。本實驗室計畫建造一台高性能的質譜儀做為我們研究的儀器。由我們比較得知，飛行時間式質譜儀是最適合我們研究彗星樣本的儀器。 　　飛行時間式質譜儀中由偵測器負責記錄各種離子抵達的時間以及此種離子的個數。本實驗室預定採用微通道板偵測器，然而此種偵測器的動態範圍只有一兩百，大大限制了我們所能測量的同位素比例的範圍以及儀器的效能，所以若能增加儀器的動態範圍對我們的研究將會有很大的幫助。本論文先介紹三種可能延展動態範圍的方法。這三種方法分別為：１、離子束切換法；２、採用裝置於Element Ⅱ® 電漿質譜儀（由Thermo Electron Corporation公司製造），擁有動態範圍達一萬以上的，可以同時輸出兩種不同放大倍率的偵測器；３、由與我們有合作關係的美國阿崗實驗室的華立．卡拉威博士所構想出的快速切換放大倍率法。 本論文的主要工作既是對這三種方法做電腦模擬或實驗。首先是用軟體Simion® 模擬離子束切換方法；接著是去實際量測Element Ⅱ® 電漿質譜儀的偵測器之切換時間；最後是建構出切換放大倍率法的實驗平台並且進行實驗。由以上的模擬及實驗結果顯示，這三種方法皆很有可能增加飛行時間式質譜儀的動態範圍。且由以上的工作我們可以得到這三種方法的優缺點。Our laboratory is developing an ultra-sensitive mass spectrometer nick-named “Dust-buster”. Its purpose is to study isotope ratio variations in individual dust grains collected by the STARDUST spacecraft from comet Wild-2. The conclusion of our preliminary study was that the best apparatus for our research is to combine laser ionization (LI) of secondary neutrals (SN) and TOF-SIMS (Time of Flight Secondary Ion Mass Spectrometry). Such an instrument will have the full mass spectrum capability of TOF while achieving 10-1000 times higher sensitivity than SIMS across the periodic table because vast majority of the sample mass loss is as neutral not ion when sputtered by primary ions. The detector is a major part of the “Dust-buster” which is responsible for recording the flight time and the intensity of each ion species. The detector we plan to use in the “Dust-buster” is micro-channel plate (MCP) detector. A potential problem is the limited dynamic range for the MCP detector which otherwise has many desirable characteristics. Three possible ways to extend the dynamic range are (1) beam-switching method, (2) using simultaneous detector which has much longer dynamic range than MCP detector, and (3) gain-switching method which was proposed by our collaborators at Argonne National Lab, Dr. Wallis Callaway. The objective of my MS thesis research is thus to check whether these methods work. The first work is the computer simulation of the beam-switching method. The second is measuring the switching time of the simultaneous detector used in the Element Ⅱ® ICP-MS manufactured by Thermo Electron Corporation. The third is to implement the idea of the gain-switching method. The approach I took was to use a Behlke switch to fast change the voltage difference across the MCP surfaces. The gain of MCP is mainly controlled by the difference of the bias voltages applied to its front and rear surfaces. Behlke switch is a type of MOSFET switch that can switch high voltage signal thousands of volts in less than 30 nano-seconds. Thus we should be able to change the voltage difference hence the gain of the MCP at high speed thus increasing its dynamic range. From the computer simulation and experiments, we know that these methods are capable of extending the dynamic range. Also from the works we can explore the out comings and short comings of each methods.誌 謝 I 中 文 摘　要 II ABSTRACT III CONTENTS V FIGURE CAPTIONS VI TABLE CAPTIONS VII CHAPTER I INTRODUCTION 1 1.1 “STARDUST” MISSION [] 1 1.2 “DUST-BUSTER” PROJECT [] 3 THE BASELINE DESIGN OF “DUST-BUSTER” WAS THAT OF MIKE PELLIN’S GROUP AT ARGONNE NATIONAL LAB. 6 1.3 DYNAMIC RANGE AND THE METHODS TO EXTEND IT 6 CHAPTER II STARDUST AND THE DYNAMIC RANGE 7 2.1 THE SIGNIFICANCE OF STARDUST 7 2.2 BENEFITS AND TRADEOFF FROM EXTENDING THE DYNAMIC RANGE 10 CHAPTER III METHODS OF EXTENDING THE DYNAMIC RANGE 13 3.1 BEAM SWITCHING 13 3.2 THE SIMULTANEOUS DETECTOR 14 3.3 GAIN-SWITCHING DETECTOR 16 CHAPTER IV EXPERIMENT EXPLORATION 22 4.1 BEAM SWITCHING: COMPUTER SIMULATION USING THE “SIMION®” PROGRAM 22 4.2 THE SIMULTANEOUS DETECTOR: PRELIMINARY CHARACTERIZATION OF THE DETECTOR ON THE ELEMENT Ⅱ® ICP-MS 25 4.3 GAIN-SWITCHING DETECTOR 27 4.3.1 Dynamic Range of Different VMCP Experiment. 27 4.3.2 Switching Time Experiment 45 CHAPTER V CONCLUSION 50 CV OF KAI-YU SHIAO 52 REFERNCE 532634522 bytesapplication/pdfen-US飛行時間質譜儀動態範圍微通道偵測器TOFMass spectrometerDynamic rangeMCPthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/54633/1/ntu-95-R93222053-1.pdf