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采用蒙特卡罗方法,利用MCNP程序计算了在中子能量为0.5—20 MeV,235U核热中子裂变源条件下,厚度为3—9 cm、碳化硼含量5%—15%的铝基碳化硼复合材料在空气、水、200—1400 ppm(1 ppm=10 6)硼酸溶液介质中的中子透射系数.结果表明:B4C/Al复合材料的透射系数随碳化硼含量和材料厚度的增加而减少,随中子能量的升高而增大,而硼酸浓度的改变对中子透射系数影响不大.B4C/Al复合材料在水中比硼酸中更能发挥其屏蔽效果,在空气中屏蔽特性显现出“反转”现象,中子能量高于5 MeV时透射系数几乎没有变化.在裂变源条件下的B4C/Al复合材料中子透射系数均比稳定源20 MeV低.介质的中子屏蔽效果是硼酸溶液>水>空气,水介质的中子透射系数与介质厚度呈指数下降关系,裂变源和稳定源条件下分别近似为e 0.71x和e 0.669x,x为厚度(cm).
The MCNP program was used to calculate the carbonization of aluminum carbide with the thickness of 3-9 cm and the content of boron carbide from 5% to 15% with the neutron energy of 0.5-20 MeV and 235U nuclear thermal fission source by Monte Carlo method. The results show that the transmittance of B4C / Al composites increases with the increase of the content of boron carbide and the thickness of the material Decreases with the increase of neutron energy, and the change of boric acid concentration has little effect on the neutron transmission coefficient.B4C / Al composites can exert its shielding effect in water more than boric acid, showing the shielding characteristics in the air When the neutron energy is higher than 5 MeV, there is almost no change in the transmission coefficient.The neutron transmission coefficient of B4C / Al composites under the fission source is lower than that of the stable source of 20 MeV.The medium of neutron The shielding effect is boric acid solution> water> air. The neutron transmission coefficient of aqueous medium decreases exponentially with respect to the thickness of the medium. The fission source and the steady source are approximately e 0.71x and e 0.669x respectively, and x is the thickness (cm).