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Concrete enclosure for shielding a neutron source

机译：混凝土外壳，用于屏蔽中子源

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In the aim to design a shielding for a 0.185 TBq 239PuBe 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 5cm up to 150cm, these calculations were repeated modeling a real source, including air, and a 1×1×1m3 enclosure with 5, 15, 20, 25, 30, 50 and 80cm-thick Portland type concrete walls. At all the points located inside the enclosure neutron spectra from 10-8 up to 0.5MeV were the same regardless the distance from the source showing the room-return effect in the enclosure, for energies larger than 0.5MeV 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.
机译：为了设计用于0.185 TBq 239PuBe同位素中子源的屏蔽，使用MCNP5代码进行了几次蒙特卡洛计算。首先，在真空中对点状源进行建模，并在从5cm到150cm的几个距离上计算中子谱和等效环境剂量，然后重复这些计算以对真实源（包括空气）和1×1×1m3进行建模。带有5、15、20、25、30、50和80厘米厚的波特兰型混凝土墙的外壳。在外壳内部，从10-8到0.5MeV的中子光谱的所有点都是相同的，无论与源之间的距离如何显示外壳中的房间返回效应，对于大于0.5MeV的能量，中子光谱都会随着距离的增加而减小增加。在外壳外部，注意到由于平均中子能量的减少，随着混凝土厚度的增加，中子光谱变得“更软”。使用环境剂量值，可以计算出混凝土厚度的衰减曲线。

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