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在中国原子能科学研究院的高压倍加器上利用中子飞行时间方法测量了2.8 Me V中子引起~(238)U裂变的瞬发中子能谱,通过增大样品量和设计合适的屏蔽体提高了效应/本底比,使得测量数据的不确定度满足预期目标(在5.5～14 Me V能区内,能量间隔为0.5 Me V条件下能谱的不确定度小于10%)。将实验几何、中子源能量分布及角分布、探测效率、束流的时间结构等实验条件输入到MCNP程序里,模拟了出射的中子谱,模拟结果与测量结果在不确定度范围内一致,验证了在入射中子能量较低时~(238)U的裂变瞬发中子谱评价数据的可靠性。
The neutron energy spectrum of ~ (238) U fission caused by 2.8 Me V neutrons was measured by the neutron time-of-flight method at the high voltage doubler of China Institute of Atomic Energy. By increasing the sample size and designing a suitable shield The effect / background ratio is increased so that the uncertainty of the measured data meets the expected target (the uncertainty of the energy spectrum is less than 10% in the 5.5-14 MeV energy range with an energy interval of 0.5 MeV). Experimental conditions such as experimental geometry, energy distribution and angular distribution of neutron source, detection efficiency and time structure of beam are input into the MCNP program to simulate the outgoing neutron spectrum. The simulation results agree well with the measurement results in the uncertainty range , The reliability of the fission instantaneous neutron spectrum evaluation data of ~ (238) U at low incident neutron energy is verified.