Kermas for various substances averaged over the energy spectra of fast neutron therapy beams: a study in uncertainties

Kermas for various substances averaged over the energy spectra of fast neutron therapy beams, as well as ratios of average kermas relative to muscle, were calculated in an attempt to estimate the uncertainties introduced in these quantities by the poor knowledge of the elemental kerma functions, actual neutron energy spectra, and composition of tissues and other materials. Average kermas have uncertainties of the order of 7%-25%, while for ratios of average kermas the uncertainties are of the order of 2%-5% for materials of clinical interest. It is concluded that the ratio of average kerma of muscle to A-150 tissue-equivalent plastic should be 0.93 +/- 0.03 for the new p + Be clinical neutron beams.     

The Preparation of a Haifnium-Free Magnesium-Zirconium Alloy by Process Separation of Hafnium

Abstract

Magnesium zirconium alloy for sheathing uranium elements in gas-cooled reactors was successfully prepared from high-purity magnesiumt and zirconium produced by the magnesium reduction of a crude oxide. Hafnium separation, suggested by a higher ratio Hf to Zr in the sludge than in the melt was considered possible owing to its higher density and melting point and its isomorphous behaviour to the strongly electropositive zirconium which readily forms compounds and exhibits a two-phase melt when added in excess of 0.5 per cent. Precipitation of excess zirconium by settling was aided by the development of a flux of high density and low inclusion-flux interfacial energy. Removal of hafnium and other high neutron capture cross-section impurities was achieved.     

Separation of zirconium from hafnium in nitric acid solutions by solvent extraction using dibutyl butylphosphonate: Part 1. Chemistry of the separation

The solvent extraction of zirconium and hafnium from nitric acid solutions into dibutyl butylphosphonate (DBBP)/Solvesso 150 has been studied, as a function of acidity, DBBP and metal concentration. Extraction of complexes containing two DBBP molecules per atom of zirconium or hafnium have been demonstrated. Separation factors for zirconium from hafnium have been obtained at different acidities and metal concentrations.     

Electrochemical Deoxidation of Solid Zirconium Dioxide in Molten Calcium Chloride

The reduction of zirconium dioxide pellets by electro-deoxidation in molten calcium chloride-calcium oxide (900 °C) has been studied. In this technique, the solid oxide is cathodically polarized against a graphite counter electrode under a constant applied potential. Unlike other metal oxides that have been reduced by this technique, only a small area around the cathodic current-collector wire was reduced to zirconium metal with zirconia pellets sintered at ~1100 °C; the rest of the sample was largely calcium zirconate. Pellets sintered above 1200 °C showed better reduction near the cathode wire and the reduction extended to the entire surface of the pellet with the passage of time. However, reduction of the inner core was found to be increasingly difficult, because the surface metal layer thickened on continuous electro-deoxidation. An analysis of the experimental results showed that the poor electrical conductivity of the intermediate compound, CaZrO₃ and its blocky morphology inhibited the electro-deoxidation process. The increase in the sintering temperature of the pellet made it better conducting. However, the pores formed in the thick zirconium metal layer in such samples were too small for an ideal contact between the inner core and the molten electrolyte and hence the reduction of the inner core remained incomplete. Within the scope of this study, it is concluded that preforms with good grain growth and porosity are necessary for the electro-deoxidation of solid zirconium oxide.     

Determination of the relative neutron sensitivity of a C-CO2 ionization chamber

The neutron sensitivity of a C-CO2 ionization chamber has been experimentally determined in the neutron energy range of 0.1-1.2 MeV. Eleven kU data were obtained which ranged from 0.04 to 0.1 as a function of neutron energy. There were two peaks in the spectrum of the kU factor, and their positions corresponded to the resonance energies of the kerma factors of carbon dioxide, of which the energies are about 0.4 and 1 MeV. The present data agree with the data obtained at the National Institute for Radiological Sciences in Chiba, Japan (NIRS). The energy dependences of the sensitivity were calculated by using the kerma and the W-value ratios of gas to soft tissue for comparison. The experimental data were reproduced well by the calculations.     

Experimental double-differential cross sections and derived kerma factors for oxygen at incident neutron energies from reaction thresholds to 65 MeV

The double-differential cross sections (energy spectra) for the (n, px), (n, dx), (n, tx) and (n, rx) reactions on oxygen have been measured for nine incident neutron energies in the range 25 to 65 MeV at lab angles between 20 degrees and 160 degrees in steps of 10 degrees. From these measurements, the energy differential cross sections have been determined and consequently the partial and total kerma factors. Based on the obtained experimental partial kerma factors in the incident neutron energy range 25-65 MeV, a procedure is proposed for the extrapolation of these values to the reaction threshold energy of each measured reaction channel. Results of the experimental double-differential, energy differential and total cross sections are presented. The deduced partial and total kerma factors of the present work are compared with results of previous measurements and theoretical predictions.     

基于塑性异化比值的金属板冲压加工性能研究

目的:研究塑性异化比值与金属板冲压加工性能之间的关系。方法:选取某金属板作为实验试样,分别在温度为350℃、400℃、430℃和450℃以及应变速率为10^-4/s、10^-3/s、10^-2/s的条件下,改变金属板试样的塑性异化比值,并计算试样冲压应变大小,比较塑性异化比值与冲压应变之间的关系。结果:当金属板塑性异化比值超出一定范围时,试样冲压应变为零,金属板出现断裂。结论:在对金属板生产加工过程中,应保证金属板的塑性异化比值控制在适当范围内,并采用爆炸焊接方法制备金属板,从而避免金属板断裂,保证金属板生产加工的质量。     

Neutron cross-sections and kerma values for carbon, nitrogen and oxygen from 20 to 50 MeV

The advent of high energy neutron radiotherapy will require the neutron cross-section data and kerma factors for elements of biomedical importance to be extended up to and possibly above 50 MeV. Nuclear model calculations have been employed to produce a set of neutron cross-sections for C, N and O from 20 to 50 MeV. The strategy employed involves the optical model fitting of experimental total cross-sections to produce elastic and non-elastic cross-sections. The non-elastic cross-section is then used to normalise the individual reaction cross-sections and charged particle spectra produced by the statistical model of level densities. Kerma values are obtained from charged particle and recoil nucleus spectra. A comparison is made with other kerma calculations, based on the intranuclear cascade-evaporation model, which are consistently lower than the results presented in this paper.     

水解法分离钪钛锆的试验研究

采用水解沉淀法从钪的反萃富集物产品中分离钪钛锆,可实现钪与绝大部分钛、锆的分离。研究发现以硫酸铵作为改性剂,可明显改善水解溶液的过滤性能。在硫酸铵用量为0.7 g/100 mL,溶液pH值为1.0,水解温度100℃,水解时间1.5 h的优化试验条件下,钛、锆的去除率可达99.56%、99.80%,钪回收率可达86.57%,成功的实现了钪与钛锆的分离,为制备高纯氧化钪创造了有利条件。     

溶液燃烧-钙还原法合成锆锰铁合金微粉

以锆、锰、铁的硝酸盐和甘氨酸为原料,采用溶液燃烧法制得超细金属氧化物前驱体,再将前驱体分别在750、850和950℃由氢化钙还原得到锆锰铁三元合金微粉.用热重/差热分析法(TG/DTA)、X射线衍射(XRD)、扫描电镜(SEM)等对溶液燃烧和钙还原2个阶段的产物进行分析与表征.结果表明:采用溶液燃烧法合成的金属氧化物前驱体颗粒分布均匀,粒度为数百纳米;采用氢化钙还原氧化物前驱体,在温度≥850℃,Ar气氛下反应1h可制得ZrMnFe三元单相合金微粉,粒度为亚微米或微米级.     

DIBK-TBP萃取分离锆铪的热力学研究

对二异丁基甲酮(DIBK)和TBP从HSCN介质中协同萃取锆铪的性能及热力学进行研究,采用对数函数外推法求得DIBK-TBP体系萃取反应的热力学平衡常数分别为log(K12,Zr)=4.73和log(K12,Hf)=-5.09,锆铪与SCN-形成配合物Zr(SCN)3+和Hf(SCN)3+的稳定性常数分别为1×109.86和1×10-0.80,而铪的分配比在硫氰酸盐存在时要大于锆的分配比,说明过渡金属离子锆和铪在硫氰酸盐存在时与一般金属离子与配位体形成的配合物的稳定性常数愈大,金属离子的分配比愈大的规律相矛盾,并计算出萃取反应的焓变分别为ΔHZr=-11.43 kJ.mol-1和ΔHHf=-7.80 kJ.mol-1,说明对锆铪的萃取反应为放热反应,升高温度不利于萃取反应的进行,常温下自由能变分别为ΔGZr=-26.54 kJ.mol-1和ΔGHf=28.57 kJ.mol-1,熵变分别为ΔSZr=51.54 J.(K.mol)-1和ΔSHf=-124.07 J.(K.mol)-1,说明铪离子比锆离子更易与SCN-形成配位键,从而生成中性分子Hf(SCN)4与有机相发生溶剂化作用而进入有机相中。     

Conditions affecting the formation of chlorinated carbon compounds during carbochlorination

The Bureau of Mines, United States Department of the Interior, has conducted an extensive study of the relationship between various metal oxide carbochlorination reactions and carbon compound byproducts. Experiments in which oxides of titanium, zirconium, and aluminum with graphite, charcoal, metallurgical coke, and pctroleum coke were chlorinated at 600° to 1000 °C produced 136 identified and quantified carbon byproduct compounds. The 20 most abundant of these compounds were correlated with reactants and reaction conditions. Experimental results support a proposed carbochlorination reaction with an initial chlorine-carbon step followed by a reaction between the resulting chlorine-carbon products and the metal oxide.     

Conditions affecting the formation of chlorinated carbon compounds during carbochlorination

The Bureau of Mines, United States Department of the Interior, has conducted an extensive study of the relationship between various metal oxide carbochlorination reactions and carbon compound byproducts. Experiments in which oxides of titanium, zirconium, and aluminum with graphite, charcoal, metallurgical coke, and pctroleum coke were chlorinated at 600° to 1000 °C produced 136 identified and quantified carbon byproduct compounds. The 20 most abundant of these compounds were correlated with reactants and reaction conditions. Experimental results support a proposed carbochlorination reaction with an initial chlorine-carbon step followed by a reaction between the resulting chlorine-carbon products and the metal oxide.     

Applications in the Nuclear Industry for Thermal Spray Amorphous Metal and Ceramic Coatings

Amorphous metal and ceramic thermal spray coatings have been developed with excellent corrosion resistance and neutron absorption. These coatings, with further development, could be cost-effective options to enhance the corrosion resistance of drip shields and waste packages, and limit nuclear criticality in canisters for the transportation, aging, and disposal of spent nuclear fuel. Iron-based amorphous metal formulations with chromium, molybdenum, and tungsten have shown the corrosion resistance believed to be necessary for such applications. Rare earth additions enable very low critical cooling rates to be achieved. The boron content of these materials and their stability at high neutron doses enable them to serve as high efficiency neutron absorbers for criticality control. Ceramic coatings may provide even greater corrosion resistance for waste package and drip shield applications, although the boron-containing amorphous metals are still favored for criticality control applications. These amorphous metal and ceramic materials have been produced as gas-atomized powders and applied as near full density, nonporous coatings with the high-velocity oxy-fuel process. This article summarizes the performance of these coatings as corrosion-resistant barriers and as neutron absorbers. This article also presents a simple cost model to quantify the economic benefits possible with these new materials. This article is based on a presentation given in the symposium entitled “Iron-Based Amorphous Metals: An Important Family of High-Performance Corrosion-Resistant Materials,” which occurred during the MSandT meeting, September 16–20, 2007, in Detroit, Michigan, under the auspices of The American Ceramics Society (ACerS), The Association for Iron and Steel Technology (AIST), ASM International, and TMS.     

Temperature modes and critical velocities when drawing the wire

When producing rod and wire wares, residual stresses are formed. This phenomenon is caused both by plastic deformation and by possible thermoplastic deformation, which appears due to contact heating the metal ware surface due to external friction forces. Undesirable residual stresses in surface layers affect the accuracy of metal wares and increase their failure probability, which is observed in the practice of drawing production. In this study, a procedure is proposed to determine the contact heating conditions from the formation prevention criteria of residual stresses. Based on thermoelasticity equations, temperature modes leading to the appearance of thermoplastic deformations are established. Critical values of the temperature difference between the drawing wire surface and the center, at which the wire surface layers transform into the plastic state with the subsequent formation of residual stresses, are determined. Limiting drawing velocities for a series of nonferrous metals (copper, zirconium, and titanium), which, if exceeded, will lead to undesirable residual stresses in the drawn wire, are determined. To increase the critical velocities, it is recommended to implement the hydrodynamic (fluid) friction mode conditions when producing metal wires.     

Effect of surface oxide films on the properties of pulse electric-current sintered metal powders

Metallic powders with various thermodynamic stability oxide films (Ag, Cu, and Al powders) were sintered using a pulse electric-current sintering (PECS) process. Behavior of oxide films at powder surfaces and their effect on the sintering properties were investigated. The results showed that the sintering properties of metallic powders in the PECS process were subject to the thermodynamic stability of oxide films at particles surfaces. The oxide films at Ag powder surfaces are decomposed during sintering with the contact region between the particles being metal/metal bond. The oxide films at Cu powder surfaces are mainly broken via loading pressure at a low sintering temperature. At a high sintering temperature, they are mainly dissolved in the parent metal, and the contact regions turn into the direct metal/metal bonding. Excellent sintering properties can be received. The oxide films at Al powder surfaces are very stable, and cannot be decomposed and dissolved, but broken by plastic deformation of particles under loading pressure at experimental temperatures. The interface between particles is partially bonded via the direct metal/metal bonding making it difficult to achieve good sintered properties.     

Thermodynamic simulation and an experimental study of the possibility of synthesizing hardened Cu–Zr–O alloys

The conditions of formation of hardened Cu–Zr–O alloys are determined theoretically and experimentally. Thermodynamic analysis of the possibility of formation of zirconium oxide in a liquid metal is performed by constructing the surface of component solubility in a metal melt. Disperse zirconium oxide inclusions in samples are detected by scanning electron microscopy and electron-probe microanalysis. The hardness and the electrical conductivity of experimental samples are measured in the as-cast state and after cold deformation. Hardness HV 133 is reached in cold-deformed samples containing 0.05 wt % Zr without heat treatment. The results obtained can be used to create a process for the formation of bulk composite materials based on copper and copper alloys.     

The chlorination kinetics of zirconium dioxide in the presence of carbon and carbon monoxide

Chlorination of zirconium dioxide, an important step in the commercial production of reactor grade zirconium metal, has been studied using carbon and carbon monoxide as reductants. Zirconium tetrachloride was produced when the oxide was reacted with chlorine alone above 1000°C; by introducing carbon the reaction temperatures could be lowered 200°C, and when carbon monoxide was used the reaction temperatures necessary for similar rates were even lower. With carbon monoxide the chlorination of zirconium dioxide is described by two regions differentiated by temperature and the dependence of reaction rate upon chlorine and carbon monoxide pressures.     

Diffusion Behavior of Mn and Si Between Liquid Oxide Inclusions and Solid Iron-Based Alloy at 1473 K

In order to clarify the changes in the composition of oxide inclusions in steel, the effect of the metal and oxide composition on the reaction between solid Fe-based alloys and liquid multi-component oxides was investigated using the diffusion couple method at 1473 K. The measured concentration gradients of Mn and Si in the metal indicated that Mn diffused into the metal from the oxide, while the diffusion of Si occurred in the opposite direction. In addition, the MnO content in the oxide decreased with heat treatment time, while the SiO₂ content increased. The compositional changes in both phases indicated that the Mn content in the metal near the interface increased with heat treatment with decreasing MnO content in the oxide. Assuming local equilibrium at the interface, the calculated [Mn]²/[Si] ratio at the interface in equilibrium with the oxide increased with increases in the MnO/SiO₂ ratio in the oxide. The difference in the [Mn]²/[Si] ratios between the interface and the metal matrix increased, which caused the diffusion of Mn and Si between the multi-component oxide and metal. By measuring the diffusion lengths of Mn and Si in the metal, the chemical diffusion coefficients of Mn and Si were obtained to calculate the composition changes in Mn and Si in the metal. The calculated changes in Mn and Si in the metal agreed with the experimental results.     

Effect of Production Parameters on the Structure of the Outer Ceramic Layer in Two-Layer Metal - Ceramic Coatings Prepared by Electron-Beam Deposition in One Production Cycle

The effect of production parameters for electron-beam deposition of two-layer metal - ceramic coatings in one production cycle on the structure and phase composition of the outer ceramic layer based on zirconium oxide stabilized with yttrium oxide is studied. It is shown that it is possible to obtain metal - ceramic coatings with the required functional properties in one production cycle.__________Translated from Poroshkovaya Metallurgiya, Nos. 3–4(442), pp. 41–48, March–April, 2005.