医院中子照射器分析室剂量场研究

Dose Field Research of Analysis Room for In-Hospital Neutron Irradiator

医院中子照射器建成后,对分析室内及其屏蔽门外的γ剂量率和中子剂量当量率进行了测量,测量结果显示:分析室内局部γ剂量率与设计值相差较大,分析室屏蔽门外γ剂量率超过原设计监督区限值7.5μSv/h,因此需对分析室内部及其屏蔽门进行屏蔽改造。根据蒙特卡罗程序模拟计算结果及实际使用情况给出最终屏蔽方案,即在分析室束流孔道所在墙面加装厚度为16cm的铅屏蔽材料屏蔽γ射线,对四周墙面及屏蔽门内侧加装厚度为1cm的含锂聚乙烯板屏蔽散射中子。改造后分析室剂量最高点γ剂量率下降277倍,中子剂量当量率下降5.8倍,屏蔽门外γ剂量率下降近90倍。

Neutron equivalent dose rate and γ ray dose rate inside the analysis room of the in-hospital neutron irradiator（IHNI） and outdoor were measured.The results show that γ ray dose rate inside the analysis room exceeds calculation value many times and γ ray dose rate outdoor is higher than supervision region dose limit of 7.5 μSv/h.According to the measurement results and the Monte Carlo simulation,the following shielding plan was adopted.Lead shielding with thinkness of 16 cm was installed on the wall,which faces the neutron beam,to shield γ ray,and lithium polyethylene plate with thinkness of 1 cm was installed on all the wall（not including ceiling and floor） to shield scattering neutron.After shielding transformation,the highest γ ray dose rate point inside the analysis room decreased 277 times,the neutron equivalent dose rate decreased 5.8 times,and the outdoor γ ray dose rate decreased nearly 90 times.