粘结碳化硼材料中子屏蔽性能及制备工艺研究

中子准直器在中国散裂中子源(CSNS)的谱仪上起着限制束流截面与发散度的作用,准直器的结构设计中通过在中子飞行管上间隔设置B4C阻挡块可以起到阻挡、吸收屏蔽杂散中子的作用,为此研制了粘结碳化硼中子阻挡块,并对其成型工艺进行了研究,确定了成型最佳粉体尺寸、粘结剂含量和固化温度.对该中子屏蔽材料的中子衰减系数计算结果表明,波长为0.1×10-10、1×10-10和15×10-10m中子通过该材料的线性衰减系数分别为3.42、30.4和449.9 cm-1.力学冲击和热重实验结果也表明该材料符合在CSNS谱仪中子束线屏蔽使用中的性能要求.     

中子源强度基准装置

中子源强度基准装置采用锰浴法绝对测量放射性核素中子源的中子发射率,可以开展中子发射率的量值传递。基准装置由内部直径110cm的球形锰池、具有2路NaI探测器的伽马测量系统以及配套的溶液循环系统和屏蔽铅室组成,改造后的基准装置参加了国际计量局组织的中子发射率国际比对(BIPM CCRI(III)-K9.AmBe.1),比对结果等效,为实现中子发射率测量结果的国际互认提供了技术依据。     

B对Pb-Mg-Al-B屏蔽功能材料的显微组织与屏蔽性能的影响

利用立式高频感应炉制备出铸造Pb-Mg-Al-B屏蔽材料,并对其显微组织和屏蔽性能进行了研究。结果表明,随着B的添加,材料组织中AlB2颗粒增多;室温抗拉强度可达105MPa,布氏硬度为160;厚度为20mm、B含量为2.0%(质量分数)的Pb-Mg-Al-B屏蔽材料对能量为250、118和65keV的X射线屏蔽率分别为90.29%、99.22%和97.9%,对γ射线的屏蔽率达到49.75%(137Cs源)和34.21%(60Co源),对中子的屏蔽率高达92.7%,说明屏蔽材料具有强度高、X(γ)射线与中子屏蔽性能优异,具备结构-功能(屏蔽)一体化的特点。     

中子和伽马射线综合屏蔽材料研究进展

核屏蔽设计的主要任务是屏蔽中子和γ射线,因此,兼具中子和γ射线综合屏蔽性能的屏蔽材料无疑是核屏蔽设计时的最佳选择。本文主要针对中子和γ射线综合屏蔽材料的种类、基质材料和性能进行了分析和综述,探讨了现有中子和γ射线综合屏蔽材料存在的主要问题,认为屏蔽材料的屏蔽性能与其他性能(如力学性能、耐热性等)之间的矛盾是屏蔽材料需要解决的关键问题。最后,展望了未来中子和γ射线综合屏蔽材料的研究方向,指出结构功能一体化屏蔽材料的研究应用是未来一大发展趋势。     

橄榄岩防辐射混凝土的试验研究

在辐射屏蔽混凝土中氢元素含量对于中子屏蔽具有重要作用,水中含有较大比例的氢元素,因此材料中的结晶水含量在辐射屏蔽混凝土制造中是一个关键因素。以富含结晶水(质量分数m6%)的橄榄岩为混凝土的粗、细集料,完成了混凝土配合比试验,配制了C30等级的防辐射混凝土。中子和γ射线屏蔽试验结果表明,同普通混凝土相比,橄榄岩混凝土中子辐射屏蔽性能明显增强,γ射线屏蔽性能也比较优异。     

新型柔性硼基苯基硅橡胶中子屏蔽材料的制备和性能研究

研制了一种新型柔性硼基苯基硅橡胶中子屏蔽材料,重点研究了不同B4C含量对复合材料的力学性能、热学性能及中子屏蔽性能的影响。结果表明:复合材料的断裂拉伸应变和拉伸强度随着B元素含量的增加有短暂的减小;复合材料的耐热性能随着B元素含量的增加而增强;复合材料的中子屏蔽性能随着B元素含量的增加而增加;纳米复合材料相比于微米复合材料在力学性能、热学性能和中子屏蔽性能方面都有一定的提高。该新型苯基硅橡胶柔性中子屏蔽材料具备应用到结构复杂、形状各异的核技术场地中的潜力,有很大的应用前景。     

纳米金涂覆微纳光纤的倏逝场氨气检测研究

本文基于TDLAS技术,采用设计制备的微纳光纤气体吸收池,搭建了一套全光纤的NH3浓度检测系统.NH3检测系统的核心部分气体传感通过1.51μm的微纳光纤完成,该系统检测结果表明,NH3在20000 ppm～100000 ppm浓度范围内,解调的二次谐波幅值与对应浓度之间具有良好的线性关系(拟合方程相关系数R=0.99...     

亚硝酸钠对10~#碳钢缓蚀作用的电化学测量

本文介绍了一套毫微安级恒电流充电曲线两点法测量系统.该系统具有连续可调、自动记录、重现性和可靠性好、误差小等特点.作者利用该体系研究了10*碳钢在100、300、600、900和1200ppm等浓度NaNO_2水溶液中的缓蚀行为,测得NaNO_2的临界缓蚀浓度为100ppm,当NaNO_2浓度超过临界浓度后,其极化电阻R_a值为一恒定值.然而,阴离子对NaNO_2缓蚀行为有影响,实验表明:SO_4~(-2)对NaNO_2缓蚀能力的影响大于C1~-.这些结果均与文献报道的数据吻合.可见,用本系统快速研究钝化体系金属腐蚀速度是可行的.     

气相色谱法测定电子混合气中B2H6含量

叙述了气相色谱法测定电子混合气中硼烷(B2H6)的方法。以热导池为检测器，H2、N2为载气。Chromosorb—W型担体涂硅油为色谱柱，在低电流(75mA)、低柱温(-40℃)和低池体温度(70℃)下，实现了对以H2、N2为底气的混合气中B2H4定量分析。当混合气中BxH6的浓度在0．10～1．0％范围时，检测极限为200ppm，分析结果的相对标准偏差小于10％。     

抗中子辐射新型含碳癸硼烷聚酯的研究

以1,2-双(4’-羧基苯基)邻碳癸硼烷和乙二醇为原料,合成出含碳癸硼烷结构的新型聚酯(简称CBR-PET),采用FT-IR、1 H NMR和GPC对其进行了表征。通过中子屏蔽实验发现CBR-PET具有显著的热中子屏蔽性能,随着样品中含硼量增加,热中子屏蔽性能增强;利用热分析技术研究了在Ar气氛下从室温~800℃的CBR-PET的热解行为,其起始分解温度约380℃,在800℃的残炭率高达72.9%。     

Emission spectroscopic determination of B and Cd in magnesium used in uranium production

An emission spectroscopic method was developed for the determination of B and Cd at trace levels in magnesium employed in the production of nuclear-grade uranium. Magnesium sample was converted to magnesium oxide and ground with pure conducting graphite powder containing LiF and Ga₂O₃. Thirty mg of the mixture was excited in a DC arc operated at 12 A. A polychromator having secondary slits for B and Cd at 249·77 nm and 228·80 nm respectively was used for recording the intensities. The method gave a mean relative standard deviation of 5·5% for B and 7·6% for Cd in the concentration range 1–10 ppm.     

Novel shielding materials for space and air travel

The reduction of dose onboard spacecraft and aircraft by appropriate shielding measures plays an essential role in the future development of space exploration and air travel. The design of novel shielding strategies and materials may involve hydrogenous composites, as it is well known that liquid hydrogen is most effective in attenuating charged particle radiation. As precursor for a later flight experiment, the shielding properties of newly developed hydrogen-rich polymers and rare earth-doped high-density rubber were tested in various ground-based neutron and heavy ion fields and compared with aluminium and polyethylene as reference materials. Absorbed dose, average linear energy transfer and gamma-equivalent neutron absorbed dose were determined by means of LiF:Mg,Ti thermoluminescence dosemeters and CR-39 plastic nuclear track detectors. First results for samples of equal aerial density indicate that selected hydrogen-rich plastics and rare-earth-doped rubber may be more effective in attenuating cosmic rays by up to 10% compared with conventional aluminium shielding. The appropriate adaptation of shielding thicknesses may thus allow reducing the biologically relevant dose. Owing to the lower density of the plastic composites, mass savings shall result in a significant reduction of launch costs. The experiment was flown as part of the European Space Agency's Biopan-5 mission in May 2005.     

添加剂LiF对FeNi粉末触媒合成金刚石的影响

研究了添加剂LiF对FeNi粉末触媒合成金刚石的影响.实验中将一定比例的无定形LiF、粉末直接添加到FeNi-C粉末体系中并均匀混合,利用高温高压条件,进行掺LiF合成金刚石的研究.实验结果表明,由于体系中LiF的掺入,对金刚石的合成条件没有明显的影响;借助X衍射测试发现,在高温高压下,体系中LiF的成份并没有发生变化;借助于光学显微镜发现,FeNi-LiF-C体系合成出的晶体晶形完整,但透明度变的很差且表面变得很粗糙,包裹体增多;通过扫描电子显微镜(SEM),对两种体系所合成金刚石表面的形貌进行了观察,发现FeNi-LiF-C体系所合成的晶体表面有凹坑出现.     

B_4C_P/PI聚酰亚胺复合薄膜耐高温及热中子辐照屏蔽性能研究

以耐高温型聚酰亚胺为基体,微米碳化硼(B_4C)为热中子吸收剂,采用粉体表面改性及超声湿混-热亚胺化成膜工艺成功制备了一系列B_4CP/PI聚酰亚胺复合薄膜,重点探讨了不同B_4C含量条件下复合薄膜的耐热性能和力学性能以及不同B_4C含量、不同复合薄膜厚度条件下复合材料的热中子屏蔽性能。研究表明:采用上述工艺,B_4C功能粒子在聚酰亚胺基体中可均匀分散;B_4CP/PI复合薄膜的耐热性随B_4C含量的增加显著提高,力学性能则呈相反趋势;所制备的B_4CP/PI复合薄膜表现出优异的热中子屏蔽性能,中子透射率I/I0随复合薄膜厚度增加及B_4C含量增加呈指数变化规律。据此,可通过材料结构设计,满足不同领域对该类耐高温中子防护材料的应用需求。     

The influences of processing parameters on forming characterizations during laser rapid forming

Laser rapid forming experiments were carried out with 316L stainless steel and nickel-base alloy to investigate the influences of the processing parameters on forming characterizations systematically. It is found that the height of a single cladding layer was very important for fabrication accuracy and forming stability of components of laser rapid forming because it was affected by almost all processing parameters and was quite difficult to precisely control. For the system with lateral powder feeding pattern, the powder injection point was the most important factor to the height control of single layer. The variation of the width of single clad, which was mainly affected by laser power, spot diameter and scanning velocity, was similar to that in laser surface melting. The surface quality was another important characterization for laser rapid forming and was remarkably affected by oxidation and the powder adhesion. In order to improve the surface quality, the flow flux of shielding gas should be 10 l min⁻¹ and the powder stream cannot be injected to the tail part of the melt pool. Based on the investigation, some metal components were fabricated.     

铜金粉电磁屏蔽导电涂料

制备了铜金粉电磁屏蔽导电涂料(E-CuZn),并将其涂覆于ABS塑料板上制成涂层,测试了屏蔽涂层的物理性能和电磁屏蔽效能,并与铜粉电磁屏蔽涂料(E-Cu)涂层进行了比较.试验证明:E-CuZn涂层屏蔽效能稳定,可以满足一定时间内的屏蔽要求.     

Shielding design studies for a neutron irradiator system based on a 252Cf source.

This study aims to investigate a shielding design against neutrons and gamma rays from a source of 252Cf, using Monte Carlo simulation. The shielding materials studied were borated polyethylene, borated-lead polyethylene and stainless steel. The Monte Carlo code MCNP4B was used to design shielding for 252Cf based neutron irradiator systems. By normalising the dose equivalent rate values presented to the neutron production rate of the source, the resulting calculations are independent of the intensity of the actual 252Cf source. The results show that the total dose equivalent rates were reduced significantly by the shielding system optimisation.     

Low frequency magnetic shielding of YBa2Cu3O7-δ: Agx high temperature superconductors

Two measurement systems were used to investigate the low frequency magnetic shielding behavior of pure YBa₂Cu₃O_7−δ, silver doped YBa₂Cu₃O_7−δ, a packed powder, a laser ablated thin film and copper. It was found that factors which influence low frequency magnetic shielding include material composition, microstructure and properties, external a.c. and d.c. fields and sample dimensions. Among the experimental materials, only bulk ceramics showed good shielding factors which were constant with frequency in the range 10–3000 Hz. A macroscopic shielding current was necessary for a good shield. The thickness of the ceramic played a crucial role in shielding. Flux breakthrough occurred when the external field exceeded a certain value. The breakthrough field increased with sample thickness. The influence of d.c. fields on the shielding behaviour depended on the history and magnitudes of the fields. Magnetic shielding hysteresis was observed and its potential application is discussed.     

A New Method for Measuring Cake Thickness by a Powder Pressure—Displacement System

An on-line powder pressure–displacement measurement system was developed based on a static measurement instrument (vernier caliper). This system consists of a pressure sensor and a displacement subsystem, and has the on-line capability to measure the thickness of powder packing with different powder sizes. The design principle employs a pressure sensor to determine the thickness by different signals generated when the pressure sensor contacts the free surface zone of powder packing and when it contacts the other powder zone. The powder materials adopted to validate this newly developed system were glass beads, sand and dust. This measurement technique can be applied under different measurement conditions.     

基于改进型两次平衡对检法的感应分压器自校准方法

介绍了参考电势变压器和指零仪变压器设计原理,分析了屏蔽间泄漏对测量结果的影响;对常规两次平衡参考电势对检法进行了改进,使零平衡和段平衡测量过程中,参考电势和测差电路均可实现等电位保护;对自校准方法进行了推导,校准结果仅与段平衡和零平衡时锁相放大器测量的电压差值相关,与参考电势变压器、指零仪变压器、辅助变压器等的误差无关,屏蔽间泄漏的影响也得到消除。对1kV感应分压器进行了校准实验,并对校准结果进行了测量不确定度分析,其相对扩展不确定度的评估结果为5.4×10^-8(k=2)。