关键词: 
飞行时间法 /
聚乙烯 /
泄漏中子谱 /
MCNP-4C程序 /
有效面积

摘要: 采用飞行时间技术测量了氘氚（D-T）源中子穿过不同厚度板状聚乙烯样品后40°方向的泄漏中子时间到达谱，样品的长和宽均为100 cm， 厚度分别为4.5， 9， 18和27 cm。 本底谱测量采用了无样本底测量和无样堵孔本底测量2种方案， 利用MCNP-4C程序模拟了相同实验条件下的泄漏中子时间到达谱， 模拟过程中考虑了源中子的能谱与角分布、脉冲中子束宽度、 探测器的效率以及样品的有效面积。通过比较发现， 采用无样测量谱作为本底时，计算值/实验值（C/E）值大于1， 并且随着样品厚度的增加而偏离1；而本底谱采用无样堵孔测量谱时， C/E小于1， 并且随着样品厚度的增加而接近1。通过对两套本底谱的分析， 并结合蒙特卡罗模拟， 计算求得了相应样品厚度下比较接近实际的本底谱，采用该模拟计算本底谱后，C/E值有了明显的改善。The neutron leakage spectrum were measured at 40° by timeofflight method for polyethylene slabs with the thicknesses of 4.5， 9，18 and 27 cm，respectively. The experimental results were compared with the MCNP-4C simulations， which carefully considered many effects， such as the angle and energy distributions of the source neutrons，the width of the beam pulse，the detection efficiency and the effective measured area. The sample out and collimatorfilled spectra were measured as the background， and the results showed that C/E values were larger than 1 when using the sample out background spectra，but smaller than 1 when using the collimatorfilled background spectra. Combine these two different background spectra， a new method was used to calculate the background spectrum，and the results have a better agreement with the simulations.