Uranium particle size

Nickel and selenium interact with incandescence on gentle heating [1], as do also sodium and potassium, the latter mildly explosively [2], Uranium [3] and zinc [4] also incandesce when their mixtures with selenium are heated, and platinum sponge incandesces vividly [5], The particle size of cadmium and selenium must be below a critical size to prevent explosions during synthesis of cadmium selenide by heating the elements together. Similar considerations also apply to interaction of cadmium or zinc with sulfur, selenium or tellurium [6], Interaction of powdered tin and selenium at 350° C is extremely exothermic [7],... 

Metzger R, McKIveen JW, Jenkins R, et al. 1980. Specific activity of uranium and thorium in marketable rock phosphate as a function of particle size. Health Phys 39 69-76. 

The influence of various gas pressure conditions within the laser ablation cell on the particle formation process in laser ablation has also been investigated.69 In LA-ICP-MS studies at low pressure (down to 2kPa) a small particle size distribution and a reduction in elemental fractionation effects was obtained. But with decreasing pressure and transport volume of ablated material, a significant decrease in the ion intensities was observed as demonstrated for uranium measurements in the glass SRM NIST 610.69 However, the laser ablation of solid materials at atmospheric pressure in LA-ICP-MS is advantageous for routine measurements due to lower experimental effort and the possibility of fast sample changing in the ablation chamber. Fractionation... 

Danesi et al.96 applied SIMS, in addition to X-ray fluorescence imaging, by using a microbeam (p-XRF) and scanning electron microscope equipped with an energy dispersive X-ray fluorescence analyzer (SEM-EDXRF) to characterize soil samples and to identify small DU particles collected in Kosovo locations where depleted uranium (DU) ammunition was employed during the 1999 Balkan conflict. Knowledge of DU particles is needed as a basis for the assessment of the potential environmental and health impacts of military use of DU, since it provides information on possible resuspension and inhalation. The measurements indicated spots where hundreds of thousands of particles may be present in a few mg of contaminated soil. The particle size distribution showed that most of the DU particles were < 5 pm in diameter and more than 50 % of the particles had a diameter of < 1.5 p.m.96... 

Uranium Dicarbide. UC2 mw 262.05 metallic crysts mp 2350—2400° bp 4370° d 11.28g/cc at 16°. Decompd by dil inorg acids, and v violently by w. Prepn is by heating a mixt of U oxide and sugar charcoal at 1370° in a C crucible by means of an electric furnace for 5 to 10 minutes. The compd emits brilliant sparks on impact, and ignites on grinding in a mortar or on heating in air to 400°. In particle sizes of less than 40 microns, it is spontaneously flammable. The dicarbide reacts with incandescence with halogens or N2 above 300°... 

The data show that the specific activity is generally not a simple function of particle size, confirming the composite nature of the samples. The sharp decrease of the 147Pm specific activities in coral burst samples toward large particle sizes is particularly significant. Systematic differences as a function of yield or soil type between refractory 147Pm behavior and semivolatile 90Sr behavior are not apparent. Uranium behaves very much like "Sr. 

Laskin, S., Measurement of Particle Size, Pharmacology and Toxicology of Uranium... 

The two Windscale piles were fuelled with natural uranium canned in aluminium. Coolant air was blown through the reactor and exhausted from a 120-m stack (Fig. 2.4). Filters were installed at the top of the stack, but were not very effective. Some fuel cans developed pinholes during operation, and others became damaged and lodged in the ducts behind the pile. It is estimated that about 20 kg of irradiated uranium were disseminated to atmosphere as oxide particles from these cans (Stather et al., 1986). The temperature of oxidation was 200-400°C. The particle size, measured at the top of the stack, showed a mass median diameter of 35 fim (Mossop, 1960). 

The particle size of Pu aerosols is very variable, depending on the mode of formation. In Fig. 5.2, curves A, B and C show size spectra obtained by Carter Stewart (1971) in laboratory experiments on the oxidation of Pu metal in air. In controlled oxidation at temperatures below the ignition point (about 500°C), scaly, friable, oxide particles were produced, with median diameter increasing with temperature. Few particles less than 1 jum in diameter were found. When the delta alloy of Pu was used, the oxide was more adherent, and the particle size larger. Increase of particle size with increase of temperature was also found in laboratory oxidation of uranium metal (Megaw et al., 1961), and was ascribed to sintering of the oxide layer. 

Metals. Nickel, sodium, potassium, uranium, zinc, and platinum sponge interact with selenium with incandescence when gently heated.3-7 The particle size of cadmium and selenium must be below a critical size to prevent explosions when making cadmium selenide this also applies to zinc.8... 

Detailed method has been developed for designing SFL. Typical results were provided for a 1,5-m diameter industrial washer for leached uranium ore, which was split into 27 particle size fractions, thus resulting in 28 simultaneous equations (Zhang and Zheng, 1982). 

The rate of deposition and clearance of uranium-containing particles from the lung depends upon its chemical form and particle size. As previously discussed in the adsorption section, most of the larger uranium particles are transported out of the respiratory system by mucocilhary action, or swallowed and eliminated in the feces. Smaller particles with higher solubilities are more rapidly absorbed into the systemic circulation but can then be excreted in the urine. 

The hazard from inhaled uranium aerosols, or any noxious agent, is determined by the likelihood that the agent will reach the site of its toxic action. Two main factors that influence the degree of hazard from toxic airborne particles are the site of deposition in the respiratory tract of the particles and the fate of the particles within the lungs. The deposition site within the lungs depends mainly on the particle size of the inhaled aerosol, while the subsequent fate of the particle depends mainly on the physical and chemical properties of the inhaled particles and the physiological status of the lungs. 

Cardiovascular Effects. No cardiovascular effects have been reported in humans after inhalation exposure to uranium. No effect on blood pressure or pulse rate was observed in a man accidentally exposed to powdered uranium tetrafluoride for 5 minutes (Zhao and Zhao 1990). Air concentration and mean particle size of the powder were not determined. Electrocardiograms and chest X-rays were normal shortly after the accident and over a 7.5-year follow-up period. 

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