With MCNP/4B code, the influence of cut-off energy, flux tallies, nuclear databases and perturbation on the reaction rate s calculation with neutron-activation method are analysed.

• 用MCNP／4B程序,对核活化法反应计算中的截断能量、通量计数方式、数据库、阈探测器之间的扰动等因素的影响作了分析。