Feasibility study: in vivo neutron activation for regional measurement of calcium using californium 252

The feasibility of using a collimated 252Cf neutron source to measure regional changes in skeletal calcium was tested because in vivo regional activation of diseased bone should offer advantages over the more widely reported total-body calcium measuring techniques. Regional activation allows examination of discrete regions where the greatest changes in calcium content occur. Additionally, a simpler radiation facility is required for regional studies. Using a 5.5-mug 252Cf source, thermal neutron flux and absorbed dose were measured in a tissue-equivalent phantom. Detection efficiency of 49Ca gamma rays for conditions simulating regional activation were measured using a 29-cm-diameter X 10-cm-thickness sodium iodide detector. These in vitro measurements indicate that a collimated 252Cf source can be used for regional neutron activation of the lower spine and legs. Preliminary calculations indicate that a 1-3-mg source provides adequate count rates for statistical accuracy with a bone marrow dosage acceptable for human patients and normal subjects.     

Application of fission track detectors to californium-252 neutron dosimetry in tissue near the radiation source

Fission track detectors were applied to a unique problem in neutron dosimetry. Measurements of neutron doses were required at locations within a tumor of 1 cm diameter implanted on the back of a mouse and surrounded by a square array of four 252Cf medical sources. Measurements made in a tissue-equivalent mouse phantom showed that the neutron dose rate to the center of the tumor was 2.18 rads micrograms-1 h-1 +/- 8.4%. The spatial variation of neutron dose to the tumor ranged from 1.88 to 2.55 rads micrograms-1 h-1. These measurements agree with calculated values of neutron dose to those locations in the phantom. Fission track detectors have been found to be a reliable tool for neutron dosimetry for geometries in which one wishes to know neutron dose values which may vary considerably over distances of 1 cm or less.     

Benchmarking the MCNP code for Monte Carlo modelling of an in vivo neutron activation analysis system

The Monte Carlo computer code MCNP (version 4A) has been used to develop a personal computer-based model of the Swansea in vivo neutron activation analysis (IVNAA) system. The model included specification of the neutron source (252Cf), collimators, reflectors and shielding. The MCNP model was 'benchmarked' against fast neutron and thermal neutron fluence data obtained experimentally from the IVNAA system. The Swansea system allows two irradiation geometries using 'short' and 'long' collimators, which provide alternative dose rates for IVNAA. The data presented here relate to the short collimator, although results of similar accuracy were obtained using the long collimator. The fast neutron fluence was measured in air at a series of depths inside the collimator. The measurements agreed with the MCNP simulation within the statistical uncertainty (5-10%) of the calculations. The thermal neutron fluence was measured and calculated inside the cuboidal water phantom. The depth of maximum thermal fluence was 3.2 cm (measured) and 3.0 cm (calculated). The width of the 50% thermal fluence level across the phantom at its mid-depth was found to be the same by both MCNP and experiment. This benchmarking exercise has given us a high degree of confidence in MCNP as a tool for the design of IVNAA systems.     

Tumorigenesis in F1 offspring mice following paternal 12.5 cGy 252Cf fission neutron irradiation

Experiments were conducted to determine whether following genetic damage at germ cell stages induced by paternal exposure to 252Cf fission neutron could lead to tumorigenesis in the offspring. Seven-week-old C3H/HeNCrj male mice were irradiated with 252Cf fission neutrons, at doses of 0 and 12.5 cGy and were mated with nine-week-old C57BL/6NCrj females two weeks after the exposure. Three weeks later, it was found that the proportion of abnormal sperm in the 12.5 cGy-irradiated males was higher than that of 0 cGy-irradiated group. Embryo lethality among the F1 offspring was also found to be higher in the 12.5 cGy group than in the 0 cGy group, while the incidence of liver tumors among the F1 offspring increased in males only. These results suggest that the paternal 12. 5 cGy radiation exposure may have caused genetic transmission of liver tumor-associated traits, which is in line with findings that show steep increase in incidence of tumorigenesis in B6C3F1.     

Determining liver retention of transuranium elements in living beagles

A method has been developed whereby the liver content of photon-emitting transuranium elements can be determined in living beagles by a combination of total-body and partial-body counting. Calibration of the system was accomplished through the photon counting of intact dogs and also of the parts of the same animals following autopsy. A determination of the calibration factors for 252Cf, 247Cf, 243Cm, 237Pu, and 241Am has been made. The special case of 252Cf was treated in which a significant fraction of the high energy fission gamma-ray spectrum penetrates the Pb shield employed in partial-body counting, and methods were developed which allow for this effect in the calculation of liver content. Some uniformity of response in the system was evident for all of the emitters which were considered. It is proposed that similar techniques could be applied in the determination of selected organ radioactivity in other species including man.     

Distinct difference in relative biological effectiveness of 252Cf neutrons for the induction of mitotic crossing over and intragenic reversion of the white-ivory allele in Drosophila melanogaster

The relative biological effectiveness (RBE) of 252Cf neutrons was determined for two different types of somatic mutations, i.e., loss heterozygosity for wing-hair mutations and reversion of the mutant white-ivory eye-color, in Drosophila melanogaster. Loss of heterozygosity for wing-hair mutations results predominantly from mitotic crossing over induced in wing anlage cells of larvae, while the reverse mutation of eye color is due to an intragenic structural change in the white locus on the X-chromosome. For a quantitative comparison of RBE values for these events, we have constructed a combined mutation assay system so that induced mutant wing-hair clones as well as revertant eye-color clones can be detected simultaneously in the same individuals. Larvae were irradiated at the age of 80 +/- 4 h post-oviposition with 252Cf neutrons or 137Cs gamma-rays, and male adult flies were examined under the microscope for the presence of the two types of clonal mosaic spots appearing. The induction of wing-hair spots per dose unit was much greater for 252Cf neutrons than for 137Cs gamma-rays, whereas the frequencies of eye-color reversion were similar for neutrons and gamma-rays. The estimated RBE values of neutrons were 8.5 and 1.2 for the induction of mutant wing-hair spots and revertant eye-color spots, respectively. These results indicate that the RBE of neutrons is much greater for mitotic crossing over in comparison to the intragenic white-ivory reversion events. Possible causes for the difference in RBE are discussed.     

Technical study for fabrication of new cermet used as inert anode in aluminum molten-salt electrolysis

In aluminum electrolysis industry, traditional carbon electrodes have many disadvantages under molten-salt corrosive conditions (970°C), such as large quantities of CO₂ production and quick consumption of carbon. The best way is cermet, which is a kind of graded composite material and consists of spinel NiFe₂O₄ as a ceramic phase and Ni-Fe-X alloy as a metal phase. The fabrication of NiFe₂O₄ powder is studied by chemical co-precipitation method with different co-precipitation chemicals (NH₃· H₂O, NaOH); differential thermal analysis and thermal gravity (TG) test have also been carried out to evaluate the performance of fabricated powder. The fabrication of Ni-Fe-X alloy is studied with three different kinds of powder compositions (NiFeAlCuZn, NiFeAlCuSn, and NiFe), different forming methods and sinter conditions are also compared and discussed in detail. DTA, XRD, density, hardness and anti-oxidation tests are carried out to test the performance of fabricated materials. Finally, fabrication technical condition of cermet is studied and determined according to graded composite slurry casting method, which combines the ceramic phase and metal phase with good performance. The fabrication technique presented in this study is valuable for making new anti-corrosion electrode material used in aluminum electrolysis. Published in Poroshkovaya Metallurgiya, Vol. 46, No. 3–4 (454), pp. 52–61, 2007.     

Influence of surface nanostructure on the life of cermet in metal cutting

Nanostructuring of the surface layer of a cermet (titanium carbide + nickel alloy) by pulsed electron-beam treatment is studied experimentally. The nanostructural characteristics of the surface of the cermet after electron-beam treatment in gas-discharge plasma containing argon, argon + nitrogen, and xenon + nitrogen improve its frictional coefficient and correspondingly extend the working life of cermet plates in metal cutting.     

A unique cascade of oxidoreductases catalyses trypanothione-mediated peroxide metabolism in Crithidia fasciculata

Parasitic trypanosomatids comprise causative agents of debilitating or life-threatening tropical diseases. The limited capacity of these parasites to cope with oxidative stress has been discussed as a target area for therapeutic approaches but success has been hampered by a lack of comprehension of their peculiar oxidant defense system depending on the unique redox metabolite trypanothione. Here we report that trypanothione-dependent hydroperoxide metabolism in Crithidia fasciculata is catalysed by two distinct proteins working in concert. One is Cf16, a unique protein which, apart from a WCPPC sequence that resembles the thioredoxin-type WCG(A)PC motif, only shows low similarity to thioredoxin-like proteins of bacteria and invertebrates. The second component is Cf21, which can be classified as a member of the peroxiredoxin family of proteins. The two proteins have been purified to homogeneity and shown to be essential for the trypanothione-dependent removal of hydroperoxides. By means of selective derivatisation of the substrate-reduced proteins the flux of reduction equivalents from trypanothione to Cf16, Cf21 and finally to the hydroperoxide was elucidated. Cf21 proved to be a moderately efficient peroxidase with broad specificity. The rate constants for the reaction of the reduced protein with H2O2, t-butyl hydroperoxide, linoleic acid hydroperoxide and phosphatidylcholine hydroperoxide were 1.0 x 10(5), 1.2 x 10(5), 1.0 x 10(5) and 0.4 x 10(5) M-1S-1, respectively. The apparent rate constant for the regeneration of reduced Cf21 by Cf16 was in the range of 1.5-3.5 x 10(6) M-1S-1. This newly discovered metabolic pathway adds two further candidates to the list of potential targets for trypanocidal drugs.     

An improved method of preparing protein and peptide probes in mass spectrometry with ionization of division fragments by californium-252 (TOF-PDMS)

The addition of organic acids (picric, oxalic, citric, or tartaric) to peptide and protein samples was found to significantly increase the yield of their quasi-molecular ions (QMI) in time-of-flight 252Cf plasma desorption mass spectrometry. The yield of the ions depended on the pKa of the acid added.     

Plasma Arc Welding of High Strength 0.3 % C–CrMoV (ESR) Steel

0.3 % C–CrMoV (ESR) steel has been proposed as an alternate cost effective material for fabrication of solid boosters for satellite launch vehicles. PAW studies on 7.8 mm thick 0.3 % C–CrMoV (ESR) steel have been conducted with filler wires of two different compositions. Welding parameters have been established for the steel. Welding has been carried out with stainless steel and copper back-up bars and effect of the same has been evaluated. Weldment has been characterized through optical microscopy, microhardness and mechanical properties evaluation. It is found that filler wire chemistry (low carbon content) does not significantly affect the properties of weldments subjected to post weld hardening and tempering treatment. It is attributed to low dilution in thicker plate welding and diffusion of carbon from base metal side during hardening treatment of the weldment. Use of different back- up bars also show similar results, except for process difficulties noted while using stainless steel. Weld efficiency >85 % has been observed with weldments having microhardness in the range of 480–520 VHN.     

Load Transfer and Recovery Length in Parallel Wires of Suspension Bridge Cables

A new simplified contact model aimed at capturing the load transfer and recovery length in parallel steel wires, commonly used in main cables of suspension bridges, is presented. The approach is based on placing elastic–perfectly plastic spring elements at the contact region between the objects. These springs have varying stiffness (Model?I) or yielding (Model?II) depending on their proximity to the clamping loads. Their stiffness or yielding is highest when they are closer to this force, and it decays when they are farther away from the clamp. This decayed behavior is assigned according to Boussinesq’s well-known solution to a point load (applied on a half space). Both models converge quickly compared with a full contact model and recover Coulomb friction law on a two-dimensional (2D) benchmark problem. Moreover, when the same properties are chosen for all springs (disregarding Boussinesq solutions), the models reduce to the classical shear-lag model, which for high clamping (point) loads gives inaccurate results. The spring models are validated experimentally on a seven-wire tightened strand. In this case study, the outer wires are axially pulled, whereas the middle wire, slightly shorter than the outer wires, experiences no direct applied axial load. However, because the strand is radially fastened at several locations, the axial load is transferred to the inner wire by an interfriction mechanism between the wires. The strains at the center points of the outer and inner wires are measured via neutron diffraction for different clamping loads, showing that the inner wire is capable of recovering most of the load.     

Continuously cast Cu-Al-Ni shape memory wires with a unidirectional morphology

The possibility of applying the Ohno continuous casting (OCC) process to the fabrication of Cu-Al-Ni shape memory alloy wires has been investigated. It was established that Cu-Al-Ni shape memory alloy wires of ∼2-mm diameter can be continuously cast by the OCC process. Cast wires were found to be of unidirectional structure with a matrix phase of β ₁ in which γ ₂ particles were precipitated in the form of dendrites along the subgrain boundaries. The γ ₂ precipitates became fewer and the size became finer with an increase in casting speed. The M _s transformation temperature was in the range −19 °C to −3 °C depending on casting speed, giving rise to stress-induced martensitic transformations at room temperature. The wires cast at slower speeds (50 to 90 mm min⁻¹) displayed shape memory attributes on heating to 90 °C, whereas the wires produced at higher casting speeds (110 to 150 mm min⁻¹) exhibited superelasticity at room temperature. In addition, the fatigue failure of the wires cast at 150 mm min⁻¹) occurred after 6500 to 7500 bend cycles, which is comparable to that of a single crystal of similar composition.     

Seismic Response Control of Building Structures with Superelastic Shape Memory Alloy Wire Dampers

This paper presents a simulation-based benchmark control study in which shape memory alloy (SMA) wire dampers are utilized to control the seismic response of a three-story nonlinear steel frame building. The SMA wire damper uses superelastic Nitinol wires for energy dissipation because of its high fatigue life and large recoverable strain. An analytical model which considers the training effect of SMA wires is used to describe the stress-strain relationship of superelastic SMA wires. The performance of SMA wire dampers is investigated in the framework of the third-generation benchmark problem on structural control. A comparative study of the seismic response control performance of SMA wire dampers with either unprestrained or prestrained SMA wires was also conducted. The results of this simulation-based benchmark control study show that SMA wire dampers, as a passive structure control measure, can effectively reduce the seismic responses of the three-story nonlinear benchmark building structure and has the potential to withstand several design earthquakes without the need for repair.     

新型 WC-MoCoB 金属陶瓷涂层制备及其性能研究

本文以碳化钨、碳化硼、钴和钼粉末为原料,按一定比例进行机械混合,采用团聚烧结工艺制备了WC-MoCoB复合金属陶瓷粉末,并利用扫描电子显微镜(SEM)、能谱分析(EDS)和X射线衍射分析(XRD)对其微观形貌、元素含量和相组成进行了表征;进而采用超音速火焰喷涂(HVOF)工艺制备了WC-MoCoB复合金属陶瓷涂层,并对涂层的微观组织、显微硬度、结合强度及抗腐蚀等性能进行研究。研究结果表明:该团聚烧结工艺制备的WC-MoCoB复合金属陶瓷粉末具有流动性好、松装密度较高的特点。该粉末经过超音速火焰喷涂加工形成的复合金属陶瓷涂层,结合强度高、孔隙率低,同时表现出优异的耐腐蚀性能。     

医用Ti(C,N)基金属陶瓷刃具的耐蚀性研究

根据外科刃具材料的性能要求，设计并制备了用于科刃具的Ti(C,N)基金属陶瓷。通过在两种医疗消毒介质中的腐蚀实际，评价了该材料的耐蚀性，并讨论了基分别在两种消毒介质中的腐蚀机理，结果表明，Ti(C,N）基金属陶瓷具有良好的耐蚀性，其在医疗消毒用次氯酸盐溶液中主要为电化学腐蚀，耐在H2O2水溶液中则以氧化腐蚀为主。     

Mo_2FeB_2复合硼化物的特性与应用

Mo_2FeB_2复合硼化物是日本新近开发的一种结构用金属陶瓷材料。本文在叙述硼化物特性的基础上,着重叙述了Mo_2FeB_2金属陶瓷的制造方法、特性及应用。     

碳量对Ti(CN)基金属陶瓷组织和性能的影响

研究了碳粉添加量对Ti(CN)基金属陶瓷组织和性能的影响。     

Beryllium Extraction and Utilisation— Prospects and Constraints

Beryllium and beryllium compounds find wide variety of applications in diverse industries. Low density, high strength, and attractive nuclear properties like low neutron absorption cross section and high scattering cross section have created great interest in the metal for space, aeronautical, and nuclear applications. The extraction technology of beryllium is now fairly well established and significant progress has also been made in the powder metallurgy fabrication of the metal. Conventional fabrication methods like rolling, wire drawing, extrusion etc. have not been found quite suitable for beryllium because of its low ductility.

This paper presents an overview of the extraction processes and the fabrication methods presently employed for beryllium metal and alloys. The various applications are described and the prospects and constraints in the large scale utilization of beryllium in industry are analysed.