Pure Spheres Research Articles

Mixed Neutron and Gamma Spectra Measurements and Calculations in Pure Iron Benchmark Assembly with Cf-252 Neutron Source

The neutron and gamma leakage spectra measurements have been made for a benchmark spherical iron assembly with diameter of 50 cm. The Cf-252 neutron sources with different emissions were placed into the centre of the iron sphere. Independent laboratories took part in the leakage spectra measurements. The proton recoil method was used with stillbene crystals and hydrogen proportional counters for neutron spectra measurement. Spectrometers using stilbene, germanium and silicon detectors were used for gamma spectra measurement. The working range of spectrometers is for neutrons in the energy range from 0.02 to 16 MeV, and for gamma from 0.40 to 12 MeV. Some adequate calculations based on different data libraries have been done and compared with measurements. The authors propose to analyse carefully the leakage mixed neutron and gamma spectrum from an iron sphere of 50 cm diameter and than adopt that field as a standard. Analogous measurements and calculations performed on pure iron spheres of diameters 20, 30 and 100 cm are briefly discussed in the report.

Depletion and “Fines” Effects on Transport in Hard-Sphere Colloids

The effect of depletion forces induced by the presence of much smaller B spheres (diameter ratio 10/1) in dense hard A spheres has been investigated. Simulations for systems of 104 spheres with mole fraction of larger spheres x A = 0.05 and with total sphere volume fraction from 0.35 to 0.655 have been carried out. The depletion force steeply increases in the A–A pair distribution function at contact, and creates a lower first coordination and more open network A-structures. There is no evidence of demixing. It is found that in the amorphous solid region there is an enhanced diffusive mobility of the larger spheres, relative to that of pure spheres, at the same densification rates. This observation resembles the “fines” effect that occurs in colloidal suspensions and granular fluids.

Ultrasonic damping in pure aluminum at elevated temperatures

Ultrasonic resonant damping was measured in polycrystalline 99.999% pure aluminum spheres between 22 and 465 °C at frequencies between 0.4 and 2.0 MHz. In fully annealed samples, the damping increases monotonically with temperature in a manner similar to that reported in numerous lower-frequency studies of a variety of materials. However, the activation energy of this increase is significantly less than values reported for aluminum at lower frequencies, and the frequency dependence is much different; these facts suggest that a different physical mechanism dominates the damping in the higher frequency range. The dependences on temperature, frequency, and vibrational amplitude are consistent with an anelastic dislocation mechanism. During recovery and recrystallization of cold-worked material, the damping drops irreversibly with a time dependence matching that expected for the dislocation density.

Matériaux de structure à modules sphériques creux en alliages de nickel microcristallisés ou amorphes

This work is part of our research program on studying the mechanical specifications of a new structural material made of hollow metallic spheres joined together by glueing or brazing. The aim of this study is to point out the effect of the structural state of the sphere alloys on the mechanical properties of the composite material. The nickel-phosphorus alloys are shown to be microcrystallized up to 8 atomic percent of metalloids, at higher phosphorous contents they are amorphus.The mechanical specifications made first on the spheres, and then on the composite, show that the breaking strength by compressing a material made of microcrystallized alloy spheres (Ni95 P5 ) is clearly higher than with a material made of pure nickel spheres.

Calculations of absorption, attenuation, and backscattering of hailstones and their possible applications

The absorption, attenuation, and backscattcring of hailstones with various structures are investigated by the model calculations of four kinds of spherical hailstones: pure ice spheres, liquid water-coated ice spheres, spongy ice-coated ice spheres, and all spongy ice spheres. All the results for the wavelength 5.56 cm, including the radar reflectivity factor, absorption factor, and attenuation factor of hailstones with different size distributions are given and discussed in this paper. The possible applications of these character-istics in radar monitoring of hailstones are also discussed. It is shown that in certain conditions, a micro-wave radiometer simultaneously operating with a radar will be helpful to the identification of the hail-bearing area. Finally, the possible influence of hailfall area on the accuracy of the measurements of the rainfall distribution by using a radar-radiometer is simply discussed.

The preparation of metal oxide spheres for use in neutron dosimetry

Gelation techniques for the preparation of spherical particles of pure and mixed metal oxide have been developed at Harwell for use in nuclear and non-nuclear applications. Gel precipitation processes have been used to prepare actinide oxide spheres (U, Th, Np and Pu) with chosen diameters in the range 50–1500 μm, principally for use as nuclear fuels. Sol-gel and gel precipitation processes have been developed to prepare oxide spheres (1–2000 μm diameter) of aluminium, silicon, titanium, zirconium and rare earth metals either as pure oxides or often with many other elements added. These materials have a variety of applications e.g. as catalysts and adsorbents. Oxide spheres can be used to advantage in neutron dosimetry because they can be fabricated directly from solutions and the spheres can be handled easily without becoming contaminated with impurities. The size of sphere can be chosen to contain the desired weight of nuclide in the range 5 μ g to 5 mg per sphere for pure oxide spheres. For the lower weights of nuclide required it is preferable to use an inert diluent such as alumina so that the sphere size can be kept large enough for easy handling. Here the nuclide of interest to diluent metal ratio is fixed at the solution stage and consequently each sphere produced contains an oxide mixture of the same composition. As an example of this technique indium-aluminium oxide spheres have been prepared.

Kinetic study of nonoxidative leaching of cinnabar ore in aqueous hydrochloric acid-potassium iodide solutions

Results obtained in a kinetic study of nonoxidative leaching of cinnabar ore in aqueous hydrochloric acid-potassium iodide solutions and the basic reactions in a new process of cinnabar treatment for obtaining mercury are presented. Experiments were performed at stirring speeds fast enough to eliminate the effect of this variable in the overall reaction rate. Under these experimental conditions the dissolution rate appears to be controlled by chemical reaction on the cinnabar surface. An activation energy of 42.3 kJ/mole was found. The dissolution rate is of the first order with respect to hydrochloric acid activity and of second order with respect to potassium iodide activity. The reaction rate in the different leaching conditions was established through weight loss of very pure cinnabar spheres submerged in the attack solution for known periods of time.

Measurement of magnetic properties of single crystal YIG by non-resonant method

A non-resonant microwave technique has been employed for the determination of saturation magnetisation (4πM s ) andg-factor of pure and Gd-doped single crystal YIG spheres yielding accurate values. It was found that 4πM s =1720–1751 g for undoped and 1595 g for 10% Gd-doped YIG spheres whileg eff=2·00–2·0039. The advantages of this method are simplicity and complete absence of propagation corrections necessary in cavity resonance experiments.

Chemically driven growth of tungsten grains during sintering in liquid nickel

Spherical tungsten particles of 200–250μm size were sintered in liquid nickel at 1640°C. Many of the tungsten spheres grow into their neighbours as reported earlier by Huppmann, Riegger and Petzow. The growing regions etch differently from the original pure tungsten spheres and consist of a tungsten alloy phase saturated with 0.15 wt.% Ni. It is therefore suggested that the driving force for this process is the chemical potential difference between the equilibrium W-Ni alloy and the pure tungsten phase being dissolved. The growth is a linear function of sintering time. The measured growth rate is 1.1 μm/min, the activation energy is (3.7 ± 0.5) × 10 5 J/mole. The kinetics appear to be controlled mainly by the solution-reprecipitation reaction at the moving boundaries. This chemically driven solution-reprecipitation process is expected to enhance the coalescence and growth of grains during sintering in the presence of liquid or solid elements which form alloys with the major component.

Convenient Magnetostatic Mode Measurement of 4nM8 of Planar-Anisotropic Ferrites

A convenient stripline technique for generating the 210 magnetostatic mode has been used to measure the 4nM8 of planar-anisotropic ferrite materials. White has described the use of magnetostatic modes as a research tool. Precision measurements by Dillon, Fletcher, and others have used waveguide cavities to obtain rf field components required to excite the desired magnetostatic modes. These techniques have been extended to permit a simple 4nM8 measurement in a nonresonant transmission line. An rf strip transmission line with a hole in the center conductor will effectively couple to the 210 magnetostatic mode of a ferrimagnetic sphere centered within the hole. The 110 mode can also be excited by axially withdrawing the sphere to a linear rf magnetic-field location. The 4nM8 of high anisotropy, hexagonal ferrites as well as more conventional cubic (YIG) ferrites have been measured using this technique. It is seen that the resonance equations for the 210 and 110 mode in a spherical resonator may be solved in general for the saturation magnetization in terms of only the externally applied magnetic fields. (ω210/γ)2=[H210−(8πMs/15)+Tx][H210−(8πMs/15)−Tz] (ω110/γ)2=(H110+Tx)(H110−Ty),=4πMs=(15/2)(H210−H110),where Tx and Ty represent anisotropy contributions. Measurement of pure YIG and MnZnY spheres indicate that the absolute values for 4nMs may be between 2 and 10% high, dependent on circuit dimensions. Additional material properties and measurement variables will be presented.