醫用迴旋加速器中子劑量

Medical Cyclotron Neutron Dose

宋主名

指導教授 ： 鍾堅

國立清華大學/原子科學院/原子科學系/碩士(2006年)

摘要

英國物理學家查德威克（James Chadwich）在1932年進行一系列實驗證明了中子的存在。中子質量與質子大約相同，提供原子核內束縛的內聚力，中子不帶電的性質，使之不受庫侖靜電力場的作用，能輕易穿透原子核。
近年來，正子斷層掃描（Positron Emission Tomography , PET）以飛快的速度崛起，成為醫學上一項重要的診斷造影模式，主要被用來確定癌症的發生與嚴重性、神經系統的狀況，及心血管方面的疾病。正子斷層掃描所需的短半衰期放射性核種由迴旋加速器負責生產，但加速器運轉過程中，核反應產生的中子會對工作人員造成傷害。雖然迴旋加速器已有完善的輻射屏蔽，但中子穿透力強，極不易衰減，可以預期仍有少量的中子會滲漏出來，所以中子對工作人員的健康影響是不能忽視的。
在花蓮慈濟醫院，迴旋加速器運轉時，我們使用不同靈敏度的氣泡式中子偵檢器在迷道內量測中子的劑量率，中子劑量率的強度可高達3650μSv/h。藉由MATLAB我們把迷道內空間劑量率的分佈顯示出來，可以觀察到迷道內空間劑量分佈並不均勻，在靠近加速器室的滑門附近有高劑量區。
使用BF3比例式中子偵檢器量測製藥室、迷道、機房和主任辦公室。我們發現迴旋加速器運轉時，中子劑量率都有增加的趨勢。2005年7月到10月有五個颱風經過花蓮，我們使用BF3比例式中子偵檢器來量測宇宙中子，並觀察宇宙中子與氣壓、雨量的關係。

關鍵字

醫用迴旋加速器 ； 中子劑量 ； 宇宙中子 ； 中子偵檢器

並列摘要

Abstract
The radiopharmaceuticals used in positron emission tomography(PET) are very short lived and generally must be produced in the hospital using a medical cyclotron. An essential byproduct during the cyclotron operation, from the point of health concern on medical personnel, is
neutron emitted from (x,yn) reactions. So neutron for medical personnel health reasons cannot be ignored.
The neutron dose rate in maze pathway of the Tzu Chi Medical Cyclotron was measured using bubble neutron dosemeters with various sensitivity during cyclotron operation, resulting a various intensity up to 3650μSv/h. Spatial distribution of neutron dose rate in the maze pathway is visualized by use of MATLAB graphical representation, reflecting the weakness of neutron shield on the slide door at the far end of the cyclotron maze pathway.
The BF3 proportional neutron counter was also utilized for measure the neutron doses in the adjacent pharmacy room, maze pathway, utility room and Director's office. We discovered neutron dose rate is surging up during cyclotron operation. In Hualien from July of 2005 to October, five typhoons passed, we also used BF3 proportional counter to measure cosmic neutron in typhoon in order to find the relation to atmospheric pressure and rainfull.

參考文獻

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