目的：量測目前國際上尚缺乏之SiemensPRIMUS直線加速器能量15MV光子所產生之光中子污染量，以作為屏蔽設計之參考。材料與方法：本研究之量測分為四部份包括（1）可攜式中子侖目儀（Harwell Co. N91），該偵檢器經影錐法校正，作為治療室周圍環境中子量測工具。（2）中子偵檢核儀模組，為BF?陘顐珥p數器外套直徑9吋與3吋聚乙烯（PE）球，作為治療室內射束外中子能量分布量測工具。（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速器照野內有無中子量。（4）粉狀五氧化二磷(P??0??)，用以度量照野內中子劑量之工具。結果與討論：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（≦0.04μSv/h）。治療室內中子平均能量分布距離等中心虛1、2、3及5公尺處分別為0.50、0.20、0.18及0.17 MeV，快中子通量率在等中心處為1.745x10?掝 cm -2s-1，慢中子通量率為1.258x10?曝cm-2 s-1，Q值經計算為小於2.17x10 ?鼆10 neutron per Gy。結論：Siemens PRIMUS直線加速器能士15MV之光子產生之光中子土為不可忽略士，屏蔽設計時需加以考量。該治療室之屏蔽工程能有效防護治療時產生之光中子污染。

　　　　　Purpose: Measuring the photoneutron contamination of 15 MV X-ray emittedfrom Siemens PRIMUS linear accelerator as to be the reference of radiation safetymanagement.Materials and Methods: This research includes four parts of measurements. (1)Portable neutron remmeter (Harwell Co. N91) which calibrated through shadow conemethod is used for environmental survey in the vicinity of treatment room. (2) Neutrondetection module, including BF3 proportional counter encased by 9 inch or 3 inchdiameter polystyrene (PE) sphere, is used for mean neutron energy distributionmeasurement in treatment room. (3) Neutron activation analysis of gold (Au)foil which is irradiated in the X rays field is administrated to determinate neutroncontamination. (4) Powder P??0?? is used to measure the thermal and fast neutronflux in the X rays field.Results and Discussion: Neutron dose equivalent rate in the points of measurementnear the treatment room is under the detection limit and is in the range of ≦0.04μ Sv/h. The distribution of mean energy of neutrons from the isocenter of 1, 2,3 and 5 m are 0.50, 0.20, 0.18 and 0.17 MeV, respectively in treatment room. Thermaland fast neutron flux at isocenter are 1.258x10?? n cm-2 s-1 and 1.745x10?掝 cm-2s-1, respectively. The Q value is less than 2.17 10 ?鼆10 neutron per Gy.Conclusion: The quantity of photoneutron in the 15 MV X-ray beam of Siemen PRIMUSlinear accelerator is not negligible and is in considerable level of shielding design.The shielding structure of this treatment room is effective for photoneutronshielding.