請用此 Handle URI 來引用此文件:
http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/32409
標題: | 飛行時間式質譜儀之動態範圍的延伸 Extend the Dynamic Range of Time-of-Flight Mass Spectrometer |
作者: | Kai-Yu Shiao 蕭凱譽 |
指導教授: | 李太楓(Typhoon Lee) |
關鍵字: | 飛行時間,質譜儀,動態範圍,微通道偵測器, TOF,Mass spectrometer,Dynamic range,MCP, |
出版年 : | 2006 |
學位: | 碩士 |
摘要: | 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. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/32409 |
全文授權: | 有償授權 |
顯示於系所單位: | 物理學系 |
文件中的檔案:
檔案 | 大小 | 格式 | |
---|---|---|---|
ntu-95-1.pdf 目前未授權公開取用 | 2.57 MB | Adobe PDF |
系統中的文件,除了特別指名其著作權條款之外,均受到著作權保護,並且保留所有的權利。