Development of a technique using MCNPX code for determination of nitrogen content of explosive materials using prompt gamma neutron activation analysis method

Nuclear-based explosive detection methods can detect explosives by identifying their elemental components, especially nitrogen. Thermal neutron capture reactions have been used for detecting prompt gamma 10.8 MeV following radioactive neutron capture by ¹⁴N nuclei. We aimed to study the feasibility of using field-portable prompt gamma neutron activation analysis (PGNAA) along with improved nuclear equipment to detect and identify explosives, illicit substances or landmines. A ²⁵²Cf radio-isotopic source was embedded in a cylinder made of high-density polyethylene (HDPE) and the cylinder was then placed in another cylindrical container filled with water. Measurements were performed on high nitrogen content compounds such as melamine (C₃H₆N₆). Melamine powder in a HDPE bottle was placed underneath the vessel containing water and the neutron source. Gamma rays were detected using two NaI(Tl) crystals. The results were simulated with MCNP4c code calculations. The theoretical calculations and experimental measurements were in good agreement indicating that this method can be used for detection of explosives and illicit drugs.     

BaTiO3陶瓷粉体凝胶注模成型的研究

为了研究BaTiO3粉体的凝胶注模成型，以聚甲基丙稀酰胺(PMAA—NH4)为分散剂，通过球磨制备稳定分散的BaTiO3浆料．采用正交实验设计原则，讨论了有机单体、交联剂和引发剂的用量对浆料的固化时间、坯体强度和密度的影响，确定最佳加入量(质量分数)分别为4％，1．5％和0．02％．在1340℃下烧结得到的BaTiO3陶瓷的晶粒尺寸均匀，气孔较少，致密度高，具有良好的PTC特性。     

直流磁控溅射BaTiO3系PTCR元件电极及其性能对比的研究

目前在钛酸钡系PTC热敏电阻器的生产过程中,广泛采用烧渗铝、化学镀镍等电极制备方法,但所制备的电极湿热老化及附着力不尽人意.本文采用直流磁控溅射法制备了的PTCR元件的底电极,实现了镍与PTCR瓷片间的欧姆接触,并发现利用溅射法工艺制备了Ni电极的元件电极附着力(垂直拉力＞3kg,剪切拉力＞0.5kg)及耐湿热老化性能均得到提高,而且溅射工艺的高成本也得到控制,在生产上实现了批量应用(日产量可达3万片).     

CaZrO3 additives to enhance capacitance properties in BaTiO3 ceramic capacitors

The effects on the dielectric properties of BaTiO₃ of addition of CaZrO₃ (0–17 wt%) has been investigated. Dielectric constants ranging between 2500 and 15 500 have been obtained by using commercial grade raw materials with the starting dielectric constant of the undoped BaTiO₃ being 800. The capacitor dielectrics have also been analysed for their electrical properties, crystalline phases and microstructural features.     

溶胶-凝胶法制备钛酸钡陶瓷纤维

首次采用乙酰丙酮作为钛醇盐的稳定剂，醋酸钡和钛酸丁酯为原料，无水乙醇-冰醋酸作为溶剂，用sol-gel法制备了长达50cm的BaTiO3凝胶纤维。用FT-IR、XRD、TGA．DTA、SEM等手段对凝胶纤维或陶瓷纤维进行一系列表征，最终得到单一钙钛矿相钛酸钡陶瓷纤维，纤维直径4～10μm，具有椭圆形截面。     

Degradation of Mn-doped BaTiO3 ceramic under a high d.c. electric field

A manganese-doped BaTiO₃ was investigated with regard to the degradation of resistivity under a high d.c. electric field. Degradation was measured as a function of time, composition and temperature, using an electric field of 3 Vm^–1. The activation energy of the process was found to be 1.13 eV. to clarify the mechanismI againstU characteristics andI againstT graphs of new, degraded and relaxed samples were studied. Electron paramagnetic resonance and potential measurements were found to be useful in describing the degradation. Finally, a brief model is put forward to account for the observed phenomena. It is based on an injection of oxygen vacancies from the anode, which is accompanied by a reduction of manganese in the lattice.Based on a thesis submitted by J. Rödel for the diploma degree at the Department of Ceramics, University of Erlangen, West Germany.     

Quantification of high alumina cement content in concrete by means of gamma ray spectrometry

A method is proposed to quantify the amount of high alumina cement (HAC) in concrete using high resolution gamma ray spectrometry. The method was tested using six samples of concrete composed of HAC and aggregates and three samples of concrete made up of aggregates and a mixture of HAC and Portland cement. The specific acitivities in Bq per kg of two isotopes of the decay series of²³⁸U (²¹⁴Pb and²¹⁴Bi) and one of the decay series of²³²Th (²²⁸Ac) were used for the quantification.

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Resume On décrit ici une méthode permettant de determiner la quantité de ciment alumineux dans les bétons, par spectrométrie gamma de haute résolution. On a utilisé l'activité spécifique du²¹⁴Pb et²¹⁴Bi de la série du²³⁸U et celle du²²⁸Ac de la série du²³²Th. La méthode a été essayée sur une série de six échantillons fabriqués avec du ciment alumineux et trois échantillons fabriqués avec un mélange de ciment alumineux et de ciment Portland.

     

立方相BaTiO_3晶体性能第一性原理研究

采用基于密度泛函理论的第一性原理研究了立方相结构钛酸钡(Ba Ti O3)晶体性能,分别从能量(价电荷密度、能带结构以及电子态密度图)、光学、及热力学角度开展了模拟计算。计算结果表明立方相Ba Ti O3属于直接带隙半导体材料,不稳定性来源于Ti和O原子之间的轨道杂化作用;光学计算表明,随着入射光能量的增加,反射分数呈无规则波动的形式,晶体的各向异性明显;在热力学方面,热焓和热容随温度升高而升高,自由能随温度升高而下降。     

晶粒可控BaTiO3-CoFe2O4磁电复合陶瓷制备及生长机制研究

采用全溶液络合法合成了BaTiO3-CoFe2O4混合粉体,用X射线衍射仪对反应产物进行了表征,分析了不同热处理温度对粉体合成的影响.用X射线衍射仪、扫描电镜对由前述预制粉体烧成的磁电陶瓷进行了微观表征,观测到由不同热处理粉体烧成的陶瓷晶粒形貌显著不同,形成了可控晶粒的磁电耦合材料.以全溶液法合成的该磁电陶瓷中,两相晶体各自析出长大,同时CoFe2O4依附于BaTiO3上生长,两种晶体因共格而形成良好的相界面层,对获得较好的磁电耦合性能作用明显.     

BaTiO3/SrTiO3超晶格的微结构研究

本实验研究利用激光分子束外延法（L－MBE）研究在SrTiO3(STO)(001)基片上生长的BaTiO3(BTO)/SrTiO3(STO)超晶格的微结构,利用小角X射线衍射光谱（SAXRD）的计算机模拟来获得BaTiO3/Sr-TiO3超晶格的微结构参数,如：总的膜厚度,超晶格周期,表面和界面的均方根粗糙度等。实验结果表明超晶格的表面和界面非常平整,均方根粗糙度大约为0.2nm,原子力显微镜（AFM）的实验研究已经证明了超晶格结构的平滑程度,超晶格的＜001＞方向存在着微弱的关联现象。     

BaTiO_3压电陶瓷的断裂韧性与晶粒尺寸及分布的研究

以压电陶瓷的自增韧作用机理为出发点,综合考虑微裂纹和气孔的双重因素影响,建立了一个断裂韧性与晶粒尺寸及分布的模型。理论分析了Ba-TiO3压电陶瓷的断裂韧性与晶粒尺寸及分布的关系;并进一步分析了大颗粒加入量对断裂韧性的影响。运用该模型得出的计算结果和实验结果具有很好的一致性。     

Intrinsic dielectric properties and lattice vibrational characteristics of single phase BaTiO3 ceramic

Journal of Materials Science: Materials in Electronics - A single phase BaTiO3 ceramic was prepared by traditional solid-state sintering process at 1220 °C for 4 h. XRD...     

In situ prompt gamma-ray activation analysis of water pollutants using a shallow 252Cf-HPGe probe

A shallow ²⁵²Cf-HPGe probe used for in situ prompt γ-ray activation of water pollutants is described. A 2.7 μg ²⁵²Cf neutron source and a 10% HPGe detector are inserted into a waterproof stainless steel probe, which is designed to be submerged and recovered in field operation. A laboratory test is performed to obtain the neutron flux distribution and prompt γ-ray contribution to the HPGe detector counts from around the submerged probe. The concentrations of toxic cadmium and chlorine in water are determined in the prompt γ-ray spectrum. The detection limit of industrial pollutants and some improvements of the current design are discussed.     

电子陶瓷用钛酸钡粉体制备工艺及其发展

对近年来国内外电子陶瓷用钛酸钡粉体制备工艺及发展进行了综述，指出了水热法由于其优良特性在近年来受到广泛关注，并预测用水热法和其它各种方法相结合的工艺必将在日后制备电子陶瓷用钛酸钡粉体工艺中占据重要地位。     

Enhanced energy storage performance of PVDF composite films with a small content of BaTiO3

Journal of Materials Science: Materials in Electronics - Polymer-based 0–3 composites filled with ceramic particles are identified as ideal materials for energy storage capacitors in electric...     

Effect of Zr on dielectric, ferroelectric and impedance properties of BaTiO3 ceramic

A polycrystalline sample of Zr-doped barium titanate (BaTiO₃) was prepared by conventional solid state reaction method. The effect of Zr (0·15) on the structural and microstructural properties of BaTiO₃ was investigated by XRD and SEM. The electrical properties (dielectric, ferroelectric and impedance spectroscopy) were measured in wide range of frequency and temperature. With substitutions of Zr, the structure of BaTiO₃ changes from tetragonal to rhombohedral. Lattice parameters were found to increase with substitution. The room temperature dielectric constant increases from ～ 1675 to ～ 10586 and peak dielectric constant value increases from ～ 13626 to ～ 21023 with diffuse phase transition. Impedance spectroscopy reveals the formation of grain and grain boundary in the material and found to decrease with increase in temperature.     

Spectroscopic study of Co-doped BaTiO3 thin films

Co-doped BaTiO₃ thin films with the perovskite structure were prepared by pyrolysis of metalorganic compounds. According to optical-absorption and luminescence data, the introduction of Co had an insignificant effect on the Curie temperatureT _C of the films (about 120δC), presumably because of the competitive effects of the Co dopant, reducingT _C , and the large compressive strain due to the thermal expansion mismatch, raisingT _C . An absorption band tentatively attributed to a small-radius polaron was observed in the near-infrared spectral region.     

Gamma-ray bursts prompt emission spectrum: an analysis of a photosphere model

A thermal radiative component is likely to accompany the first stages of the prompt emission of gamma-ray bursts (GRBs) and X-ray flashes. We analyse the effect of such a component on the observable spectrum, assuming that the observable effects are due to a dissipation process occurring below or near the thermal photosphere. For comparable energy densities in the thermal and leptonic components, the dominant emission mechanism is Compton scattering. This leads to a nearly flat energy spectrum (nuFnu proportional, 0) above the thermal peak at approximately 10-100 keV and below 10-100 MeV, for a wide range of optical depths 0.03 less, similar tau less, similar 100, regardless of the details of the dissipation mechanism or the strength of the magnetic field. For higher values of the optical depth, a Wien peak is formed at 100 keV to 1 MeV. In particular, these results are applicable to the internal shock model of GRBs, as well as to slow dissipation models, e.g. as might be expected from reconnection, if the dissipation occurs at a sub-photospheric radii. We conclude that dissipation near the thermal photosphere can naturally explain (i) clustering of the peak energy at sub-MeV energies at early times, (ii) steep slopes observed at low energies, and (iii) a flat spectrum above 10 keV at late times. Our model thus provides an alternative scenario to the optically thin synchrotron-synchrotron self-Compton model.     

Effect of CuO–BaO mixture content on the grain growth of BaTiO3

The present work has been aimed at studying the effect of processing variables such as amount of additions, sintering temperature, and duration on the density, microstructure, and grain growth of BaTiO3/CuO–BaO ceramics. Grain growth of BaTiO3 during liquid-phase sintering is investigated for CuO–BaO (mole ratio, CuO/BaO=2.5) mixture additions from 0.5 wt% to 2 wt%. Sintering in air for 1 to 16 h at 950 °C to 1250 °C is studied. BaTiO3 with 0.5 wt%, 1 wt%, 1.5 wt%, and 2 wt% CuO–BaO mixture additions, the average grain growth exponents are 5.3, 4.3, 5.9, and 9.2 and the activation energies are 605±60, 348±19, 650±50, and 810±110 kJ mol-1, respectively. For all compositions, the grain growth exponents decrease with increasing sintering temperature. © 1998 Chapman & Hall