Abstract
本論文主要探討以高純度鍺偵檢器(HPGe)作為現場快速量測放射性氣體偵 檢系統。一般核反應器在正常運轉時會釋放一些微量放射性氣體Ar、Kr、 Xe。本系統的設計乃針對密閉場內及戶外均勻瀰漫放射性氣體作一度量。 系統是由可攜帶式高純度鍺偵檢器及多頻道分析儀所組成，可作為移動式 偵測系統，且本系統無須利用幫浦抽氣、濾紙吸附等程序，是以可作到定 性、定量、瞬時、線上的量測。論文概分為二部份：(1) 利用自行製備氣 體射源Ar41、Kr85m及Xe125,Xe133,Xe135 均勻瀰漫於密閉室內，對單一 高純度鍺偵檢器作一瀰漫放射性氣體效率校正。由實驗所得之最低可測濃 度和可應用的範圍作一討論。(2) 同時利用三台不同型號高純度鍺偵檢器 作一效率校正，觀察不同型號高純度鍺偵檢器效率和晶體體積之關係。實 驗結果顯示在 (1)效率和能量在對數座標上呈一線性關係可看出實驗的準 確性，且偵檢系統之最低可測濃度遠低於法規規定之最大許可濃度，故可 應用於核災、核戰放射性氣體偵測器，作到事前預警之功效。 (2)三偵檢 器晶體體積和相對效率有一線性相關，故不同型號高純度鍺偵檢器在急需 時，可利用此一線性相關作一效率推導，事後再補以實驗證明。本文中針 對瀰漫放射性氣體度量所建立的實驗方法及不同體積晶體偵檢器效率與體 積關係之推導，均有深入淺出的解說。在單一偵檢器度量部分。吾可發現 加馬能量在200keV以後的偵測效率乃呈一線性關係，可看出實驗準確度相 當不錯。且偵檢器GC1019在單一及三台偵檢器實驗中所得之偵測效率相近 ，可看出再現性佳。是以嚴謹的實驗過程及統計方法的品質管制，乃是本 實驗準確性及再現性的主要關鍵。而在三台不同體積晶體偵檢器，實驗結 果在200keV之後偵測效率均呈線性關係，且實驗斜率值和點射源理論斜率 值相近，可看出實驗準確度佳。此外本實驗的最低可測濃度均遠低於最大 許可濃度，是以可作為環境監測器。如預使最低可測濃度值更低，可使用 效率較佳偵檢器利用本實驗法做一校正。整套偵測系統均為可攜帶式，是 以待發展成熟可作為環測之偵測系統。 The purpose of this study is to examine the applicabi- lity of real-time monitoring of gaseous radionuclide with a high- purity germanium (HPGe) detector. In the case of normal operations, continuous release of gaseous radio- nuclides of tracer amount of isotopes of Ar,Kr and Xe from reactor is found. The system, consisted of portable HPGe and multichannel analyzer (MCA), is designed for the measurement both in sealed chamber and in outdoors sur- rounded with gaseous radionuclide. Besides, quantitative, qualitative, prompt and on-line measurement can be reached with the movable detectors without air sucking pump and filter paper. The research was divided into two major parts as follows : (1) The HPGe detector was calibrated by using of artificial gaseous Ar-41,Kr-85m and Xe-125,133,135 releas- ed to a sealed chamber. Minimum detectable concentration and possible application field monitoring are discussed. (2) Three various types of HPGe detectors were calibrated, the relationship between detectors' efficiency and the crystal volume was observed. The results show : (1)linear relationship between eff- iciency and energy in log coordinate can be obtained. The detector system is available for the measurement of minimum detectable concentration (MDC) far less than legal maximum permissible concentration (MPC), application to detect the gaseous radionuclide of nuclear disaster and nuclear war.(2) There exists a linear relationship between crystal volume and relative efficiency so that the inter- relation between efficiencys with various detectors can be developed in emergenecy.