| 摘要： | 中文摘要PDF ; 英文摘要PDF
| 且且: 量測目前國際上尚缺乏之S i e m e n s PRIMU S 直線加速器能量的M V 光子所產生之光中子污染量， 以作為屏蔽設計之參考。
姐姐盟主法: 本研究之量測今為四部份包括( 1 ) 可攜式中子侖自儀( H a附e ll Co. N91 ) ，該偵檢器經影錐法校正， 作為治療室周圍環境中子量j貝IJ 工具。( 2 ) 中子偵檢核儀模組， 為B F， 比例計數器外套直徑9吋與3吋聚己倫( P E ) I芋， 作為治療室內射束外中子能量至于布量測工具。( 3 ) 金片，做為中子活化分析工具， 利用中子活化分析之高靈敏度確定加遠器照野內有無中子量。( 4 ) 粉狀五氯化二磷( P， 0 5 ) ，用以度量fl!l野內中子劑量之工具。
益基盟主立益. 經可攜式中子侖目儀量測，治療室外中子等效劑量率皆與背景值相當( 星0 . 0 4μ卻I h ) 。治療室內中子平均能量分布距離等中心處l 、2 、3 及5 公尺處勞別為0 . 5 0 、。鈞、0 . 1 8及0 . 1 7 MeV ﹒ 快中子通量率在等中心處為1.7 4 5 X 104 n em" 5,1 . 慢中子通量率為1. 2 5 8 x 10' n em"5, 1 , QlL直經計算為小於2 .17 X l Ol l neutronper Gy 。
益益S i e m e n s PRIMUS 直線加速器能量1 5 MV 之光子產生之光中子量為不可忽略量， 屏蔽設計時需加以考量。該治療室之屏蔽工程能有效防議治療時產生之光中子污染。 |
| Purpose : Measuring the photoneutron contamination of 15 MY X-ray emitted from Siemens PRIMUS linear accelerator as to be the reference of radiation safety management.
Materials and Methods: This research includes four parts of measurements. (1) Portable neutron remmeter (Harwell Co. N91) which calibrated through shadow cone method is used for environmental survey in the vicinity of treatment room. (2) Neutron detection module, including BF3 proportional counter encased by 9 inch or 3 inch diameter polystyrene (PE) sphere, is used for mean neutron energy distribution measurement in treatm ent room. (3) Neutron activation analysis of gold (Au) foil which is irradiated in the X rays field is administrated to determin ate neutron conta minatio n. (4) Powder P20 S is used to measure the thermal and fast neutron flux in the X rays field.
Results and Discussion: Neutro n dose equivalent rate in the points of measurement near the treatment room is under the detection limit and is in the range of ~ 0.04)..l Sv/h. The distributi on of mean energy of neutrons from the isocenter of I, 2, 3 and 5 m are 0.50, 0.20, 0.18 and 0.17 MeY, respectiv ely in treatment room. Thermal and fast neutron flux at isocenter are 1.258 x io' n ern" s' and 1.745 x 104 n ern" s', respectively. The Q value is less than 2.17 x io" neutron per Gy.
Conclusion: The quantity of photoneutron in the 15 MY X-ray beam of Siemen PRIMUS linear accel erator is not negligibl e and is in considerable level of shielding design. The shielding structure of this treatment room is effective for photoneutron shielding. |
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