3DHZETRN-v2 includes a detailed three dimensional (3D) treatment of neutron/light-ion transport based on a quasi-elastic/multiple production assumption allowing improved agreement of the neutron/light-ion fluence compared with results of three Monte Carlo (MC) codes in the sense that the variance with respect to the individual MC results is less than the variance among the MC code results. The current numerical methods are no longer the main limitation to HZETRN code development and further changes in the nuclear model are required. In a prior study, an improved quasi-elastic spectrum based on a solution of the transport approximation to nuclear media effects showed promise, but the remaining multiple-production spectrum was based on a database derived from the Ranft model that used Bertini multiplicities. In the present paper, we will implement a more complete Serber first step into the 3DHZETRN-v2 code, but we retain the Bertini–Ranft branching ratios and evaporation multiplicities. It is shown that the new Serber model in the 3HZETRN-v2 code reduces the variance with individual MC codes, which are largely due to nuclear cross section model differences. The code will be available through the software system, OLTARIS, for shield design and validation and provides a basis for personal computer software capable of space shield analysis and optimization.

3DHZETRN-v2包括基于准弹性/多重生产假设的中子/轻离子输运的详细三维（3D）处理，与三个蒙特卡洛（MC）的结果相比，可以改善中子/轻离子通量的一致性相对于各个MC结果的方差小于MC代码结果之间的方差的意义上的代码。当前的数值方法不再是HZETRN代码开发的主要限制，需要对核模型进行进一步的更改。在先前的研究中，基于对核介质效应的运输近似解的解决方案，改进的准弹性谱显示出了希望，但其余的多重生产谱是基于使用Bertini多重性的Ranft模型得出的数据库。在本文中，我们将在3DHZETRN-v2代码中实现更完整的Serber第一步，但我们保留了Bertini-Ranft分支比和蒸发多重性。结果表明，3HZETRN-v2代码中的新Serber模型减少了单个MC代码的方差，这主要是由于核横截面模型的差异。该代码可通过软件系统OLTARIS获得，用于屏蔽设计和验证，并为能够进行空间屏蔽分析和优化的个人计算机软件提供基础。