In a small neutron radiography system such as DIANE, which is basedo n a sealed-tube neutron generator, the maximum possible efficiency of fast neutron thermalization must be achieved, consistent with realistic industrial and manufacturing practices. To this end, MCNP simulations and experiments have been performed for further enhancing the performance of the moderator/collimator assembly in the DIANE. These calculations and experiments have shown that a fast neutron reflector/multiplier can be useful in increasing the number of fast neutrons entering the moderator. Various heavy metals with high inelastic cross sections for fast neutrons and low capture cross sections have been tested. Results indicate that the best moderating materials for this application are beryllium, zirconium hydride, and high-density polyethiene, and the best reflector/multiplier material for this use is tungsten. The MCNP calculations incdicate that for a fast neutron output of 4 x 10~(11) n s~(1-) in 4 #pi# steradians, a DIANE can be fabricated which produces a thermal netron beam for radiography having a flux of approximately 2.1 x 10~5 n cm~(-2) s~(-1) at an effective collimator ratio of 30, or about 7.5 x 10~4 n cm~(-2) s~(-1) at a collimator ratio of 50.
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机译：在诸如Diane的小中子放射线照相系统中，必须实现快速中子热化的最大可能效率，与现实的工业和制造实践一致。为此，已经进行了MCNP模拟和实验，以进一步提高Diane中的主持人/准直器组件的性能。这些计算和实验表明，快节奏反射器/乘数可以用于增加进入主持人的快节空间的数量。已经测试了具有快速中子和低捕获横截面的具有高非弹性横截面的各种重金属。结果表明，该申请的最佳调节材料是铍，氢化锆和高密度聚烯烯，以及用于此类使用的最佳反射器/乘法器材料是钨。 MCNP计算中的快速中子输出为4×10〜（11）ns〜（1-）在4＃pi＃steradians中，可以制造一个侧田，其产生用于射线照相的热网束，其通量约为2.1 x 10〜5 n cm〜（-2）s〜（-1）以有效的准直器比为30，或约7.5×10〜4 n cm〜（-2）s〜（-1）的准直器比50。
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