GEANT4 used for neutron beam design of a neutron imaging facility at TRIGA reactor in Morocco
GEANT4 used for neutron beam design of a neutron imaging facility at TRIGA reactor in Morocco
复制标题
DOI：
10.1016/j.nima.2011.02.096
复制
发表时间：
2011-09
影响因子：
1.4
通讯作者：
A. Ouardi;A. Machmach;R. Alami;A. Bensitel;A. Hommada
中科院分区：
文献类型：
--
作者：
A. Ouardi;A. Machmach;R. Alami;A. Bensitel;A. Hommada
中子成像具有广泛的应用范围，并在金属基体中的含氢物质的可视化和定量方面发挥了关键作用。随着新的中子成像设备的安装，该领域继续扩展到新的应用领域。在这个范围内，目前正在摩洛哥的Maamora核研究中心围绕2.0 MW TRIGA MARK-II反应堆开发用于计算机断层扫描和实时中子射线照相的中子成像设施（Reuscher等人，1990 [1]; de Menezes等人，2003 [2]; Deinert等人，2005 [3]）。中子成像装置由中子准直器、实时中子成像系统和成像处理系统组成。为了减少中子束中的γ射线含量，选择了切向通道。在功率为250 kW时，在切向通道入口处测得的热中子注量率约为3× 10 ~（11）ncm ~ 2/s。该设施将以锥形中子准直器为基础，该准直器带有两个直径分别为4厘米和2厘米的圆形光阑，分别对应于165和325的长径比。这些隔膜的尺寸允许在良好的通量和有效的L/D比之间达成妥协。采用了会聚-发散准直器几何结构。束线由γ过滤器、快中子过滤器、中子慢化器、中子和γ快门、准直器周围的生物屏蔽和几级中子准直器组成。采用全三维数值代码GEANT 4进行蒙特卡罗计算，以设计中子束线（http：//www.info.cern.ch/asd/geant4/geant4.html [4]）。为了提高中子热束的质量，几种材料，主要是铋（Bi）和蓝宝石（Al 2 O3）分别作为伽马和中子过滤器进行了检查。GEANT 4模拟表明，可以分别使用铋（Bi）和蓝宝石（Al 2 O3）过滤器过滤伽马和超热中子和快中子。为了得到一个好的镉比，GEANT 4模拟被用来定义在辐射通道入口的慢化剂的设计。22 cm厚的石墨块似乎是最佳的中子慢化剂。结果表明，5cm的铋与5cm的蓝宝石的组合允许以相当大的方式过滤伽马射线、超热中子以及快中子，而不影响中子热通量。
Neutron imaging has a broad scope of applications and has played a pivotal role in visualizing and quantifying hydrogenous masses in metallic matrices. The field continues to expand into new applications with the installation of new neutron imaging facilities. In this scope, a neutron imaging facility for computed tomography and real-time neutron radiography is currently being developed around 2.0MW TRIGA MARK-II reactor at Maamora Nuclear Research Center in Morocco (Reuscher et al., 1990 [1]; de Menezes et al., 2003 [2]; Deinert et al., 2005 [3]). The neutron imaging facility consists of neutron collimator, real-time neutron imaging system and imaging process systems. In order to reduce the gamma-ray content in the neutron beam, the tangential channel was selected. For power of 250kW, the corresponding thermal neutron flux measured at the inlet of the tangential channel is around 3×1011ncm2/s. This facility will be based on a conical neutron collimator with two circular diaphragms with diameters of 4 and 2cm corresponding to L/D-ratio of 165 and 325, respectively. These diaphragms' sizes allow reaching a compromise between good flux and efficient L/D-ratio. Convergent–divergent collimator geometry has been adopted. The beam line consists of a gamma filter, fast neutrons filter, neutron moderator, neutron and gamma shutters, biological shielding around the collimator and several stages of neutron collimator. Monte Carlo calculations by a fully 3D numerical code GEANT4 were used to design the neutron beam line (http://www.info.cern.ch/asd/geant4/geant4.html[4]). To enhance the neutron thermal beam in terms of quality, several materials, mainly bismuth (Bi) and sapphire (Al2O3) were examined as gamma and neutron filters respectively. The GEANT4 simulations showed that the gamma and epithermal and fast neutron could be filtered using the bismuth (Bi) and sapphire (Al2O3) filters, respectively. To get a good cadmium ratio, GEANT 4 simulations were used to define the design of the moderator in the inlet of the radiation channel. A graphite block of 22cm thickness seems to be the optimal neutron moderator. The results showed that the combination of 5cm of bismuth with 5cm of sapphire permits the filtration of gamma-rays, epithermal neutrons as well as fast neutrons in a considerable way without affecting the neutron thermal flux.