中国科学家发明了可屏蔽中子和伽马射线的无铅复合屏蔽材料

诸平

Fig.1 Schematic diagram of shielding mechanism of modified nano composite shielding material. Credit: Huo Zhiping

Fig. 2. (a) Comparison of neutron transmittance between nano/micro composite materials and modified nano/micro composite materials (b) Comparison of neutron transmittance of various composite materials at thickness of 4.5 cm and 15 cm (Image by HUO Zhiping) 

据中国科学院（Chinese Academy of Sciences）2021年12月23日提供的消息，中科院合肥物质科学研究院等离子体物理研究所（Institute of Plasma Physics,  Hefei Institutes of physical science, Chinese Academy of Sciences）的科研人员与中国科技大学（University of Science and Technology of China）的科研人员合作，发明了可屏蔽中子和伽马射线的无铅复合屏蔽材料（Scientists Invent Lead-free Composite Shielding Material for Neutron and Gamma-Ray----Chinese Academy of Sciences）。

来自中国科学院合肥物理科学研究院的霍志鹏博士（Dr. Huo Zhipeng音译）和他的学生赵盛（Zhao Sheng音译）最近开发了一种无铅复合屏蔽材料，该材料对于中子和伽马射线具有高屏蔽性能，并且对环境友好。他们的研究结果于2021年11月23日已经在《核材料与能源》（Nuclear Materials and Energy）杂志网站发表——Zhipeng Huo, Sheng Zhao, Guoqiang Zhong, Hong Zhang, Liqun Hu. Surface modified-gadolinium/boron/polyethylene composite with high shielding performance for neutron and gamma-ray. Nuclear Materials and Energy, Available online 23 November 2021, Volume 29, 101095.  DOI: 10.1016/j.nme.2021.101095. https://doi.org/10.1016/j.nme.2021.101095

通过一系列复杂而全面的实验，对改性氧化钆/碳化硼/高密度聚乙烯(gadolinium oxide/boron carbide/high density polyethylene简称Gd₂O₃/B₄C/HDPE)复合材料进行了安全有效的屏蔽中子和伽马射线的测试。

中子作为一种电中性粒子，具有很强的穿透性，在粒子碰撞过程中会发出二次伽马射线（secondary gamma rays）。科学有效的屏蔽中子方案是同时选择高Z(原子序数)材料、低Z材料和吸中子材料进行复合屏蔽。然而，含铅材料的生物毒性限制了其应用。

稀土元素钆（gadolinium）在自然界中通常以无毒的Gd₂O₃的形式存在，一直表现出较高的平均热中子吸收、耐高温和良好的伽马屏蔽性能。研究人员首先研究了Gd₂O₃的屏蔽机理，然后采用偶联剂对Gd₂O₃表面进行修饰，以改善Gd₂O₃在基体中的界面相容性和分散性。

从事辐射和环境保护多年的霍志鹏博士说：“它是无铅的，对环境和人类都没有威胁。”他进一步解释了辐射屏蔽系统的工作原理。快中子与钆(Gd)发生非弹性碰撞，与氢发生弹性碰撞，直到它们变成为热中子，最后被高Z元素钆和硼吸收。

实验结果（experimental results ）表明，在Cf-252环境下，在15 cm厚度条件下，此复合材料的中子屏蔽率可达98%。在Cs-137和Co-60环境中，在相同厚度下，此复合材料的伽马屏蔽率分别为72%和60%。

其综合屏蔽性能优于常规的硼聚乙烯准直屏蔽（boron-polyethylene collimating shielding），适用于实验先进超导托卡马克(Experimental Advanced Superconducting Tokamak简称EAST)的中子能谱和伽玛能谱诊断系统。据研究人员称，它有望成为一种有前途的中子-伽马混合场辐射屏蔽材料。

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科学岛团队在核辐射防护材料性能研究方面取得新进展

A new polythene-B4C based concrete for shielding  

Highlights

• A series of surface modified-gadolinium/boron/polyethylene composite was prepared.

• The modification of fillers improved the interfacial compatibility and dispersion in HDPE.

• The neutron and gamma shielding performance were significantly improved by modification.

Abstract

A series of surface modified-gadolinium/boron/polyethylene composites composed of surface modified fillers (M−microGd₂O₃ and M−nanoGd₂O₃) are prepared for shielding neutron and gamma radiation. Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray energy spectrometer (EDS) reveal that the surface modification of fillers significantly improved the interfacial compatibility and dispersion in the polyethylene matrix. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and mechanical tensile tests show that the modification of nanoGd₂O₃ and microGd₂O₃ improve the thermal stability and mechanical property of the composites. The T_5% (initial decomposition temperature), T_p(endothermic peak temperatures) and Tensile strength of 10 wt% M-nanoGd₂O₃/20 wt% B₄C/70 wt% HDPE reachs 463.5℃,137.2℃, and 19.6 MPa, which is greatly improved compared with unmodified materials and neat HDPE. The neutron and gamma shielding mechanism of the composites is studied both by experimental measurements and Monte Carlo simulation. The results show that the improved interfacial compatibility and dispersion of fillers in the polyethylene matrix effectively enhances the neutron and gamma shielding rate. The shielding performance of the composite blended with M−nanoGd₂O₃ is significantly better than that of the composite blended with M−microGd₂O₃ and the unmodified materials with the relatively thin thickness. Finally, a superior composite containing 10 wt% M−nanoGd₂O₃/20 wt% B₄C/70 wt% HDPE reaches a neutron shielding rate of 90% at 9.1 cm under Cf-252 environment, and a gamma shielding rate of 70% at 13.7 cm under Cs-137 environment, which have the characteristics of lead free, low specific gravity and high shielding performance and is expected to be a promising radiation shielding materials used in neutron-gamma mixed fields.