Gamma-ray detection via D(γ, n)H neutron counting

The photodisintegration of deuterium (Q = −2.22 MeV) in combination with a neutron counter has been used to detect high-energy γ-rays. The γ-ray source is surrounded by a tank filled with heavy water and the emitted neutrons are counted in 4π geometry with neutron detectors embedded in a graphite moderator. The absolute detection efficiency of a small test system (1.8 1 D₂O) has been determined for E_γ = 2.6–8.1 MeV and found to agree well with calculations (e.g., 8.0 × 10⁻⁵ at E_γ = 4.4 MeV). It is proposed that the system should be useful for the study of capture reactions induced on highly radioactive targets. Improvements in detection efficiency as well as limitations in data analyses are discussed.     

Thermophysical properties of rubidium and lithium halides by γ-ray attenuation technique

The temperature dependence of linear attenuation coefficient, density and thermal expansion of rubidium halides (RbCl, RbBr and RbI) and lithium halides (LiCl, LiBr and LiF) has been studied by γ-ray attenuation technique. The γ-ray attenuation studies have been carried out using a γ-ray densitometer. The mass attenuation coefficients (μ _m ) of rubidium and lithium halides have been determined using γ-beam of different energies viz. (0.0595, 0.662, 1.173 and 1.332 MeV) respectively. The variation of density and coefficients of temperature dependence of density have been measured using Cs (0.662 MeV) source. The values of density at different temperatures have been used to estimate the values of linear attenuation coefficients (μ _l ) of the alkali halides studied in the present work for other γ-energies. The variation of thermal expansion of alkali halides studied in the present work has been compared with the results obtained from other methods. The variation in these thermophysical properties have been represented by linear equations. Volume thermal expansion coefficients and mass attenuation coefficients (μ _m ) of these compounds for the different energies have been reported and compared with data calculated by empirical and experimental method.     

相变装置中填充泡沫金属的传热强化分析

通过对泡沫金属结构的分析,将泡沫金属结构简化为二维的循环扩展六边形网格形式,且传热单元被分为九个导热层。在此基础上以热阻分析推导出了在泡沫金属作为填充材料时其整体有效导热系数Koff与泡沫金属空隙率ε之间的数学关系式。分别以泡沫铜、泡沫铝填充石蜡为例与用铜、铝翅片并联和串联两种方式填充石蜡时的有效导热系数进行了计算对比,从计算结果可以明显看出采用泡沫金属作为填充材料,其整体效果要优于翅片,可显著改善相变储能装置的传热性能及储能效率。     

Correlation of temperature factors with physical properties in cubic elements

The recommended value of the Debye-Waller thermal parameter, B, for 22 cubic elements, based on experimental measurements using X-ray, neutron, and -ray diffraction as well as high-voltage electron diffraction, has recently been published. Using these data, interesting correlations can be made of the parameter B with thermal, mechanical and defect properties of these cubic elements. These results show an evident relationship between the microscopic and bulk properties.     

Novel biopolymer-coated hydroxyapatite foams for removing heavy-metals from polluted water

3D-macroporous biopolymer-coated hydroxyapatite (HA) foams have been developed as potential devices for the treatment of lead, cadmium and copper contamination of consumable waters. These foams have exhibited a fast and effective ion metal immobilization into the HA structure after an in vitro treatment mimicking a serious water contamination case. To improve HA foam stability at contaminated aqueous solutions pH, as well as its handling and shape integrity the 3D-macroporous foams have been coated with biopolymers polycaprolactone (PCL) and gelatine cross-linked with glutaraldehyde (G/Glu). Metal ion immobilization tests have shown higher and fast heavy metals captured as function of hydrophilicity rate of biopolymer used. After an in vitro treatment, foam morphology integrity is guaranteed and the uptake of heavy metal ions rises up to 405 μmol/g in the case of Pb²⁺, 378 μmol/g of Cu²⁺ and 316 μmol/g of Cd²⁺. These novel materials promise a feasible advance in development of new, easy to handle and low cost water purifying methods.     

Construction and properties of a gamma-ray detector based on D(γ, n)H neutron counting

The photodisintegration of deuterium with subsequent neutron counting has been used in a system to detect high-energy γ-rays. The system consists of a cylindrical tank filled with 242 l of heavy water and surrounded by 30 ³He-filled proportional counters. Details of the construction, specifications and characteristics of the detector are described. The detector has been used to measure the hexadecapole strength of the 2506 (J^π = 4⁺) → 0 (J^π = 0⁺) keV γ-ray transition in ⁶⁰Ni (E4 = 78 nuclear physics applications, it is proposed that the detector be used for studies relevant to nuclear astrophysics, in particular for the study of capture reactions induced on highly radioactive targets (up to about 1 Ci). The detector is also useful for neutron work (18% neutron efficiency).     

The deformation of brittle starch foams

There exists a theoretical model to describe the deformation of solid foams which relates the mechanical properties to the foam density and the cell-wall properties. Previous work has assumed that the wall properties are constant for a wide range of different density foams and can be characterized by the properties of the unfoamed material. In this paper we show that, when considering extruded starch foams, variation of the extrusion parameters in order to produce different bulk density foams has an effect on the cell-wall material: notably upon the crystallinity,T _g and wall density. Therefore, both the bulk foam and cell-wall mechanical properties were measured in order to test the full theory. For the relative fracture stress, excellent agreement was found between the predicted power law behaviour and the experimental results. However, the power law for the relative modulus is larger than the predicted value.     

Aluminium foam–polymer composites: processing and characteristics

Dissemination of closed cell metal foam unique properties (low density, efficient energy absorption, high vibration/sound attenuation) in real life products has often been difficult to realise. With advanced pore morphology (APM) aluminium foam–polymer hybrids a new and simplified process route targeted at application in foam-filled structures (e.g. automotive A-pillar) has been introduced. APM foams are made from spherical, small volume foam elements joined to each other in a separate process step. Joining the aluminium foam elements by adhesive bonding delivers composite foam with approximately 80–95 wt.% aluminium foam and 5–20 wt.% adhesive (polymer). Setting up cellular structures from spherical foam elements allows for automatic part production, good pore morphology control and cost effective aluminium foam application. An automated production line is displayed and discussed. Mechanical properties of APM aluminium foam–polymer hybrids are similar to other closed cell aluminium foams. Integration of APM foams in profiles resulted in significantly improved properties as observed for conventional closed cell aluminium foam fillings. The unique properties of APM composite foams make them an attractive alternative as a cost effective and easily applicable material of construction with targeted uses such as energy absorbing reinforcement of composite structures.     

Structural changes of polyacrylonitrile precursor fiber induced by γ-ray irradiation

The structural changes of polyacrylonitrile precursor fibers under γ-ray irradiation were studied. The Fourier transform infrared spectroscopy (FTIR) results indicated that chemical reactions occurred in the irradiated fibers. The thermal and thermal mechanical behaviors of the fibers, which were characterized by differential scanning calorimetry (DSC), thermal gravimetry (TG) and thermal mechanical analysis (TMA), changed under irradiation, since ladder structure had formed in the fibers under irradiation prior to the heating process. The crystallinity and crystallite size were found to decrease with the increase of irradiation time, as the chemical reactions induced by γ-ray irradiation affected the crystal structure of the fibers. γ-ray irradiation may be useful in accelerating the thermal stabilization of PAN precursor fibers.     

Piezoresistive and compression resistance relaxation behavior of water blown carbon nanotube/polyurethane composite foam

The in-situ bulk polycondensation process in combination with a ball milling dispersion process was used to prepare the water blown multiwall carbon nanotubes (CNT)/polyurethane (PU) composite foam. The mechanical properties, piezoresistive properties, strain sensitivity, stress and resistance relaxation behaviors of the composite foams were investigated. The results show that the CNT/PU composite foam has a better compression strength than the unfilled polyurethane foams and a negative pressure coefficient behavior under uniaxial compression. The resistance response of CNT/PU nanocomposites foam under cyclic compressive loading was quite stable. The nanocomposite foam containing a weight fraction of carbon nanotubes close to the percolation threshold presents the largest strain sensitivity for the resistance. The characteristic of resistance relaxation of CNT/PU composite foam is different from the stress relaxation due to the different relaxation mechanism. During compressive stress relaxation, the CNT/PU foam composites have excellent resistance recoverability while poor stress recoverability.     

Crystal growth and thermal neutron scintillation response of Ce doped KLiYF5

K⁶Li(Y_1−xCe_x)F₅ (x = 0.003, 0.02) single crystals were grown from the melt using the precise atmosphere control type Micro-Pulling-Down (μ-PD) method to examine their potential as a new thermal neutron scintillators. The grown crystals were single-phase materials as confirmed by XRD. The crystals demonstrated 40-60% transmittance above 320 nm and Ce³⁺ 5d-4f luminescence observed around 340 nm when exited by α-ray. The radio luminescence measurements under thermal neutron excitation (²⁵²Cf) demonstrated the light yield of 890 (Ph/neutron) and the decay time excited by α-ray exhibited 20 and 259 ns.     

Deformation characteristics of metal foams

The deformation behaviour of a series of aluminium and zinc foams was investigated by uniaxial testing. Because the deformation behaviour of metal foams is expected to be anisotropic owing to the existence of a closed outer skin and with respect to the foaming direction, a series of measurements was carried out where the orientation of the outer skin and the foaming direction were varied. Stress–strain diagrams and corresponding compression strengths were determined for aluminium- and zinc-based foams. The influence of an age-hardening heat treatment was investigated. Finally, the axial deformation behaviour of aluminium tubes filled with aluminium foam was tested under uniaxial loading conditions. The results of the measurements are discussed in the context of possible applications of metal foams as energy absorbers. © 1998 Chapman & Hall     

Determination of the parahydrogen fraction in a liquid hydrogen target using energy-dependent slow neutron transmission

The NPDGamma collaboration is performing a measurement of the very small parity-violating asymmetry in the angular distribution of the 2.2 MeV γ-rays from the capture of polarized cold neutrons on protons (A_γ). The estimated size of A_γ is 5×10⁻⁸, and the measured asymmetry is proportional to the neutron polarization upon capture. Since the interaction of polarized neutrons with one of the two hydrogen molecular states (orthohydrogen) can lead to neutron spin-flip scattering, it is essential that the hydrogen in the target is mostly in the molecular state that will not depolarize the neutrons (≥99.8% parahydrogen). For that purpose, in the first stage of the NPDGamma experiment at the Los Alamos Neutron Science Center (LANSCE), we operated a 16-l liquid hydrogen target, which was filled in two different occasions. The parahydrogen fraction in the target was accurately determined in situ by relative neutron transmission measurements. The result of these measurements indicate that the fraction of parahydrogen in equilibrium was 0.9998±0.0002 in the first data taking run and 0.9956±0.0002 in the second. We describe the parahydrogen monitor system, relevant aspects of the hydrogen target, and the procedure to determine the fraction of parahydrogen in the target. Also assuming thermal equilibrium of the target, we extract the scattering cross-section for neutrons on parahydrogen.     

含油制冷剂在泡沫金属圆管内流动沸腾的换热特性

实验研究了填充泡沫金属的圆管内制冷剂与润滑油混合物流动沸腾换热特性。实验对象为两根分别填充5PPI、90%孔隙率与10PPI、90%孔隙率泡沫铜的圆管,以及相同管径的光管。实验工况为蒸发压力995kPa,质流密度为10~30 kg/(m2.s),热流密度为3.1~9.3kW/m2,入口干度0.175~0.775,油浓度为0~5%。实验结果表明:纯制冷剂工况下,泡沫金属的存在强化流动沸腾换热,换热系数最多提高185%;含油工况下,泡沫金属强化换热的效果弱化;相同工况下,更小的孔径可以提高流动沸腾换热系数,相比5PPI泡沫金属的实验数据,10PPI的泡沫金属可以使换热系数最多提高0.6倍。基于流型建立了填充泡沫金属的圆管内制冷剂与润滑油流动沸腾换热系数的预测模型,预测模型与98%的实验数据误差在±30%以内。     

Mechanical and physical characterization of copper foam

A lost carbonate sintering process in powder metallurgy has been used to prepare copper foam of low to medium porosities with controlled pore size, shape, and distribution. The compressive properties of the copper foams have been investigated for different metal volume fractions ranging from 15–100%. The elastic moduli measurements in good agreement with Mori-Tanaka predictions for the two-phase mixtures. The microstructure, the electrical resistivity, and the thermal conductivity were also studied.     

Compressive properties of aluminum foam produced by powder-Carbamide spacer route

Effects of cell shape and size, and relative density of aluminum foam on its compressive behavior have been investigated. Aluminum foams were produced via aluminum powder-Carbamide spacer route. The results show that angular cells significantly reduce mechanical properties of the foam. They also indicate that compressive properties of the foams, including plateau stress (σ_pl), densification strain (ε_D), and energy absorption, increase by cell size and relative density of the foams. Experimental results were compared with theoretical predictions; they were fairly corresponded to theoretical conceptions; this arises from near-ideal architecture of the foams with almost spherical cells, in this study. Constant values of C, n and α in theoretical modulus and densification strain equations wear calculated as 1.22, 2.09 and 0.95, respectively. The values indicate compressive behavior approaches to ideal morphology foam via employing spherical space holder.     

Characterization of rigid polyurethane foams containing microencapsulated Rubitherm<Superscript>®</Superscript> RT27: catalyst effect. Part II

Catalyst Tegoamin 33 has been used for the synthesis of rigid polyurethane (RPU) foams containing microencapsulated Rubitherm^® RT27 and having a high mechanical resistance. These materials could be employed in buildings for thermal insulation and thermal energy storage (TES). The fillers content influence on the foaming process and also the foam properties was evaluated. It was observed that a foam containing up to a 18 wt% of microcapsules can be manufactured, improving the TES capacity while maintaining the mechanical properties of the neat foam. Besides, it was observed that the mechanical resistance of foams synthesized using catalyst Tegoamin 33 are higher than those obtained when catalyst Tegoamin BDE was employed, with the mechanical resistance of the foam containing 21 wt% being higher than those of foams synthesized with catalyst BDE containing only 11 wt% of fillers while maintaining the advantages of an improvement in TES capacity. A general model of reaction curve of n tank-in-series of a same time constant was used to fit the rising curves. This model allowed to predict the final volume of the synthesized foam. Finally, TES capacities and mechanical properties of the synthesized foams were in the range of those reported in literature. Moreover, foam densities satisfied the restriction established by the Spanish regulation for building applications.     

Metal foaming by a powder metallurgy method: Production, properties and applications

 A method for fabricating metal foams based on the powder metallurgy process is presented. This foaming process allows for the production of complex-shaped foam parts, metal foam sandwich panels and foam filled hollow profiles. A range of alloys can be foamed using this method including aluminum, zinc, tin, lead and steel. The as-produced part has a closed-cell microstructure and a high fraction of porosity (typical range from 40–90% porosity). Selected mechanical properties of metal foams are evaluated, including the loading of foam samples with and without face skins and the axial crushing of tubular structures with foam reinforcement. Potential applications are discussed such as light-weight construction and energy absorption for both military and civilian uses. Received: 22 July 1998 / Accepted: 4 September 1998     

A study of fabricating and compressive properties of cellular Al–Si (355.0) foam using TiH2

Al–Si (355.0) alloy foam has been produced by Alporas method (in which foam alloy melts, and titanium hydride is used as a blowing agent). Mechanical behavior such as quasi-static compression (strain–stress curves, energy absorption capacity), also the effects of thermal properties on the macroscopic structure of the produced foam were investigated. In addition, the effect of energy absorption capacity on percentage porosity has also been studied. The research shows that the produced foam with an average cell size and proper distribution has a more mechanical stability compared to the foams with no such characteristics. It was found that yield strength tends to increase from 12.51 MPa for porosity 74.0% to 22.32 MPa for porosity 54.0%. This foam has also been compared with other foams such as Al-pure foam and Mg foam. It can be stated that Al–Si (355.0) foam has a higher yield strength in comparison to Al-pure foam and Mg foam.