Vega-Carrillo H R, Villagrana-Muñoz L E, Rivera-Perez E, de Leon-Martinez H A, Soto-Bernal T G, Hernández-Davila V M
Unidad Académica de Estudios Nucleares de la Universidad Autónoma de Zacatecas, C. Ciprés 10, Fracc. La Peñuela, 98068 Zacatecas, Zac., Mexico.
Appl Radiat Isot. 2013 Sep;79:37-41. doi: 10.1016/j.apradiso.2013.04.030. Epub 2013 May 6.
In the aim to design a shielding for a 0.185 TBq (239)PuBe isotopic neutron source several Monte Carlo calculations were carried out using MCNP5 code. First, a point-like source was modeled in vacuum and the neutron spectrum and ambient dose equivalent were calculated at several distances ranging from 5 cm up to 150 cm, these calculations were repeated modeling a real source, including air, and a 1×1×1 m(3) enclosure with 5, 15, 20, 25, 30, 50 and 80 cm-thick Portland type concrete walls. At all the points located inside the enclosure neutron spectra from 10(-8) up to 0.5 MeV were the same regardless the distance from the source showing the room-return effect in the enclosure, for energies larger than 0.5 MeV neutron spectra are diminished as the distance increases. Outside the enclosure it was noticed that neutron spectra becomes "softer" as the concrete thickness increases due to reduction of mean neutron energy. With the ambient dose values the attenuation curve in terms of concrete thickness was calculated.
为设计用于0.185太贝克勒尔（239）钚铍同位素中子源的屏蔽装置，使用MCNP5代码进行了多次蒙特卡罗计算。首先，在真空中对点状源进行建模，并在5厘米至150厘米的多个距离处计算中子能谱和环境剂量当量。对包含空气的真实源以及带有5厘米、15厘米、20厘米、25厘米、30厘米、50厘米和80厘米厚波特兰型混凝土墙的1×1×1立方米围护结构重复进行这些计算。在围护结构内所有点处，能量从10^(-8)直至0.5兆电子伏的中子能谱无论距源的距离如何均相同，显示出围护结构中的室反效应；对于能量大于0.5兆电子伏的情况，中子能谱随距离增加而减弱。在围护结构外，注意到由于平均中子能量降低，随着混凝土厚度增加中子能谱变得“更软”。根据环境剂量值计算了混凝土厚度方面的衰减曲线。
