- 期刊
LiF:Mg，Cu，P熱發光劑量計能量依持性與角度依持性研究
Investigation of Energy and Angular Dependence for LiF: Mg, Cu, P Thermo Luminescent Detectors
摘要
LiF:Mg，Cu，P熱發光劑量計(Thermo luminescent detectors)以近似人體組織的等效原子序、劑量回饋線性、迴火程序簡便、穩定度高等優點成爲近年來各研究單位使用頻率非常高的一項度量工具。除了行之有年的美國Harshaw熱發光劑量計外，中國DML（Solid Dosimetric Detector & Method Laboratory，固體劑量探測器和方法研究實驗室）研究團隊也發展出另一以GR系列命名的LiF:Mg，Cu，P熱發光劑量計。即便相同製造商、同一批次的LiF:Mg，Cu，P熱發光劑量計，每一顆劑量計所含有的活化劑比例並不完全相同，因此也難保劑量計本身對於輻射線的敏感度、再現性等特性參數有相同輸出結果。本實驗使用此二廠商：GR與Harshaw的LiF:Mg，Cu，P熱發光劑量計進行能量依持性與角度依持性的特性研究。輻射源使用核研能研究所國家游離輻射標準實驗室之中能量X射線系統及銫－137與鈷－60射源來評估兩劑量計面對不同光子能量時的能量依持反應；並藉台北三軍總醫院放射腫瘤部之直線加速器以6MV與15MV兩種高能光子能量，搭配旋轉角度來觀察角度依持性。實驗結果指出，即便GR-200熱發光劑量計本身因敏感度較高而使得在低能量區段有高估的情形，但面對不同入射光子能量時，能量依持反應的範圍與變異係數較TLD-100H來的小；截然不同地是，GR-200在面對不同入射角度時，因光子能量變化幅度較大，使得角度大於±60°以上對其依持性就有明顯變化。即使兩劑量計對能量或角度依持特性有近似的反應行爲，但GR-200的高敏感度容易對實際情形有誤判的可能，此點對使用者應謹慎考慮。
並列摘要
The characteristics of energy and angular dependence dependences of two types of commercial LiF: Mg, Cu, P detectors, GR-200 and TLD-100H are examined in this study. The energy dependence was determined performing irradiation with the X-ray beams M80, Ml00, M120, M150, IW200, IW300 and with the gamma reference radiation of l37Cs and 6OCo. To angular dependence of the TLDs was determined for the angles 0 , ±15°, ±30°, ±45 , ±60° and ± 75° using 6 MV and 15 MV X-ray fields. The energy dependence irradiations were performed at the National Radiation Standard Laboratory, Taiwan and the angular dependence irradiations were performed at Tri-Service General Hospital, Taipei. For energy and angular dependence, there was no significant difference between the types of commercial TLD. In addition, there was also no significant difference within each type with respect to the doses delivered or energies irradiated. In all the results of measurements, the thermo luminescent sensitivity of GR-200 was higher than TLD-100H by 10% to 28%.