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1.
W. C. Roman 《Plasma Chemistry and Plasma Processing》1981,1(1):83-111
Prior results indicate techniques have been developed for fluid mechanical confinement of high-temperature uranium hexafluoride (UF6) plasma for long test times while simultaneously minimizing uranium compound deposition on the walls. Follow-on investigations were conducted to demonstrate a UF6/argon injection, separation, and reconstitution system for use with rf-heated uranium plasma confinement experiments applicable to UF6 plasma core reactors. A static fluorine batch-type regeneration test reactor and a flowing preheated fluorine/UF6 regeneration system were developed for converting all the nonvolatile uranium compound exhaust products back to pure UF6 using a single reactant. Pure fluorine preheat temperatures up to 1000 K resulted in on-line regeneration efficiencies up to about 90%; static batch-type experiments resulted in 100% regeneration efficiencies but required significantly longer residence times. A custom-built, ruggedized time-of-flight (T.O.F.) mass spectrometer, sampling, and data acquisition system permitted on-line quantitative measurements of the UF6 concentrations down to 30 ppm at various sections of the exhaust system; this system proved operational after long-time exposure to corrosive UF6 and other uranium halides. 相似文献
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While the bottom-up protein analysis serves as a mainstream method for biological studies, its efficiency is limited by the time-consuming process for enzymatic digestion or hydrolysis as well as the post-digestion treatment prior to mass spectrometry analysis. In this work, we developed an enzyme-free microreaction system for fast and selective hydrolysis of proteins, and a direct analysis of the protein digests was achieved by nanoESI (electrospray ionization) mass spectrometry. Using the microreactor, proteins in aqueous solution could be selectively hydrolyzed at the aspartyl sites within 2 min at high temperatures (∼150 °C). Being free of salts, the protein digest solution could be directly analyzed using a mass spectrometer with nanoESI without further purification or post-digestion treatment. This method has been validated for the analysis of a variety of proteins with molecular weights ranging from 8.5 to 67 kDa. With introduction of a reducing agent into the protein solutions, fast cleavage of disulfide bonds was also achieved along with high-temperature hydrolysis, allowing for fast analysis of large proteins such as bovine serum albumin. The high-temperature microreaction system was also used with a miniature mass spectrometer for the determination of highly specific peptides from Mycobacterium tuberculosis antigens, showing its potential for point-of-care analysis of protein biomarkers.A high-temperature microreaction system is developed for fast and selective hydrolysis of proteins, enabling direct analysis of protein biomarkers by mass spectrometry. 相似文献
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The technique of pyrohydrolysis has been applied to the determination of fluorine in the fluorides of scandium, yttrium, and the lanthanons. These fluorides have been divided into two classes according to their rate of hydrolysis. Lutetium, ytterbium, cerium(III), scandium, gadolinium, terbium, dysprosium, holmium, erbium, and thulium florides can be hydrolyzed in 30 min or less. Yttrium, lanthanum, praseodymium, neodymium, samarium, and europium fluorides require from 45 to 150 min for complete hydrolysis. Accelerators, such as uranium oxide (U3O8), chromium(III) oxide, and a mixture of these oxides have been used successfully to reduce the tune required for quantitative hydrolysis of the fluorides in the latter group. The use of the correct accelerator reduces the hydrolysis time to 30 min or less for all these fluorides except lanthanum, praseodymium and neodymium. 相似文献
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D. S. Pashkevich G. G. Shelopin D. A. Mukhortov V. B. Petrov Yu. I. Alekseev V. S. Asovich 《Russian Journal of Applied Chemistry》2004,77(11):1847-1853
Synthesis of lower perfluoroalkanes (tetrafluoromethane, hexafluoroethane, octafluoropropane, decafluorobutane) by high-temperature reaction of graphite with fluorine in a fluidized bed was studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 11, 2004, pp. 1865–1871.Original Russian Text Copyright © 2004 by Pashkevich, Shelopin, Mukhortov, Petrov, Alekseev, Asovich. 相似文献
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The mechanism of the gas-phase reaction UF 6 + H 2O --> UOF 4 + 2HF is explored using relativistic density functional theory calculations. Initially, H 2O coordinates with UF 6 to form a 1:1 complex UF 6.H 2O. Over an activation energy barrier of about 19 kcal/mol, H 2O transfers a H atom to a nearby ligand F, resulting in UF 5OH + HF. The eliminated HF or another H 2O molecule may form a hydrogen bond with UF 5OH. Starting from UF 5OH, the second HF elimination results in UOF 4. If UF 5OH is in the isolated form, UF 5OH --> UOF 4 + HF takes place over a barrier of 24 kcal/mol. If UF 5OH is hydrogen-bonded with H 2O or HF, the conversion barrier is less than 10 kcal/mol. Once formed, the unstable UOF 4 tends to associate with additional ligands and hydrogen-bonding donors. The calculated binding energies indicate the significance of such interactions, which may have profound impact on further HF eliminating reactions. The IR spectra features can be used to indicate the formation and interaction type of the intermediates and products. 相似文献
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H. Sakurai M. Fukuda Y. Hayashibe Y. Sayama K. Masumoto T. Ohtsuki 《Journal of Radioanalytical and Nuclear Chemistry》1997,217(2):267-271
A highly sensitive determination of fluorine in standard rocks by photon activation using the19F(,n)18F reaction combined with pyrohydrolysis for the separation of18F has been reported. The irradiation energy was operated at 20 MeV to avoid the interference from Na, because Na is one of the major element in rocks and18F is also produced from Na via23Na(,n)18F reaction above its threshold energy, 20.9 MeV. After irradiation, fluorine was extracted by pyrohydrolysis and separated as LaF3 precipitate. It was ascertained that the average recovery of fluorine in standard rocks was about 90% and the precipitate was of high radiochemical purity. This method was applied to the analysis of ten GSJ rock reference samples and two USGS standard rocks issued by the Geological Survey of Japan and the United States Geological Survey, respectively. The detection limit of this method was 0.02 g/g, and the results obtained by this method were in good agreement with the recommended values. This method was easily applied to the determination of a few ppm level of fluorine in rock samples, such as ultrabasic rock and feldspar. 相似文献
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The use, for analysis, of prompt gamma-rays excited by 5 MeV alpha-particles from the reactions19F(α,α′γ)19F,19F(α, nγ)22Na and19F(α, pγ)22NE, was studied. The precision of the analyses depended on the gamma-ray energy used for the measurement. Relative standard
deviations were ±1.8, ±0.9 and ±1.3% using the 110-, 197- or 1275 keV gamma-rays. The method was tested with N. I. M. standard
materials of calcium fluoride and fluorspar, and was used as a rapid method for the determination of fluorine in cements. 相似文献
12.
Florian Kraus Dr. Sebastian A. Baer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(33):8269-8274
From the reaction of uranium hexafluoride UF6 with dry liquid ammonia, the [UF7(NH3)]3? anion and the [UF4(NH3)4] molecule were isolated and identified for the first time. They are found in signal‐green crystals of trisammonium monoammine heptafluorouranate(IV) ammonia (1:1; [NH4]3[UF7(NH3)] ? NH3) and emerald‐green crystals of tetraammine tetrafluorouranium(IV) ammonia (1:1; [UF4(NH3)4] ? NH3). [NH4]3[UF7(NH3)] ? NH3 features discrete [UF7(NH3)]3? anions with a coordination geometry similar to a bicapped trigonal prism, hitherto unknown for UIV compounds. The emerald‐green [UF4(NH3)4] ? NH3 contains discrete tetraammine tetrafluorouranium(IV) [UF4(NH3)4] molecules. [UF4(NH3)4] ? NH3 is not stable at room temperature and forms pastel‐green [UF4(NH3)4] as a powder that is surprisingly stable up to 147 °C. The compounds are the first structurally characterized ammonia complexes of uranium fluorides. 相似文献
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There is a growing interest in determination of low Z elements, i.e. carbon to phosphorus, in various samples. Total reflection X-ray fluorescence spectrometry (TXRF) has been already established as a suitable trace element analytical method with low sample demand and quite good quantification limits. Recently, the determinable element range was extended towards Z = 6 (carbon). 相似文献
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Characterization of uranium particles produced by hydrolysis of UF6 using SEM and SIMS. 总被引:1,自引:0,他引:1
Ruth Kips Ann Leenaers Gabriele Tamborini Maria Betti Sven Van den Berghe Roger Wellum Philip Taylor 《Microscopy and microanalysis》2007,13(3):156-164
Environmental sampling (ES) is a powerful technique used by safeguards inspectors of the International Atomic Energy Agency and the European Safeguards Office for the detection of undeclared nuclear activities. Since its implementation in the 1990s, ES has proven to be very sensitive and effective. Considering the consequences, the measurements should be carried out under a quality management programme. At the Institute for Reference Materials and Measurements, a new production method is under development for the preparation of reference uranium particles from well-certified UF6, allowing uranium particles with certified isotopic abundances to be prepared that are representative of those found in uranium enrichment facilities. Using an aerosol deposition chamber designed and built for the purpose, particles are formed by the hydrolysis of UF6 and their morphology and (isotopic) composition measured using SEM-EDX and SIMS. The SEM measurements show that by varying the relative humidity of the air in the reaction chamber, the morphology of the particles can be changed. By making a distribution map of the chemical composition of the particles, the relationship between fluorine and uranium as main constituents of the particle could be established. The presence of fluorine is a valuable indicator for the occurrence of nondeclared enrichment activities. 相似文献
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Summary Air-dust samples with masses of 12 mg each were analysed instrumentally for their nitrogen and fluorine content by photon activation. The samples were irradiated with photons of maximum energy,E
max=15MeV. The nuclear reactions14N(, n)13N and19F(, n)18F give two positron emitters. The positrons react with electrons, emitting annihilation radiation. The 511-keV peak of the annihilation radiation of13N and18F is measured simultaneously and the decay curve is taken. The half-lives of 9.96 and 109.7 min allow a quantitative separation. By choosingE
max=15 MeV for the activation we eliminate interference from carbon and oxygen. The activation threshold for the n,-reaction of carbon is 18.72 MeV and for oxygen 15.67 MeV, while the activation threshold for N is 10.55 MeV and for F 10.44 MeV. The detection limit for the instrumental method is 4g for both nitrogen and fluorine.
Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980. 相似文献
Die Analyse von Stickstoff und fluor in Luftstaubproben durch Photonenaktivierung
Zusammenfassung An Luftstaubproben von 12 mg Masse konnte der Gehalt an Stickstoff und Fluor durch Photonenaktivierung zerstörungsfrei bestimmt werden. Die Proben wurden mit Photonen einer Energie von Emax=15 MeV bestrahlt. Die 511-keV-Linie der nach14N (, n)13N und19F (, n)18F entstandenen Nuklide wurde simultan gemessen und die Zerfallskurve aufgenommen. Die Halbwertszeiten 9,96 und 109,7 min liegen so weit auseinander, daß eine quantitative Trennung möglich ist. Durch Wahl der Aktivierungsenergie treten keine Störungen durch Sauerstoff und Kohlenstoff auf, da die Aktivierungsschwellen für die, n-Reaktionen von C bei 18,72 MeV und von O bei 15,67 liegen, während sie für N bei 10,55 MeV und für F bei 10,44 MeV liegen. Die Nachweisgrenzen liegen beim zerstörungsfreien Verfahren bei 4g für N und für F.
Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980. 相似文献
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Summary By using the photonuclear activation technique, fluorine has been determined in biological materials. After alkali fusion, fluorine is adsorbed on an anion exchange resin. The irradiated resin sample is soaked and stirred in 5N hydrochloric acid solution. After filtering, fluorine-18 resulting from the (, n) reaction was extracted with 0.2 % dimethyldichlorosilane in xylene. The fluorine-18 0.51 MeV annihilation peak in an aliquot of the organic phase was measured by gamma-ray spectrometry. The precision of this method calculated from replicate analyses of standard specimen is ±11 % and sensitivity is estimated as 0.01g for this element.
Zusammenfassung Mit Hilfe der photonuklearen Aktivierung wurde Fluor in biologischem Material bestimmt. Nach der Alkalischmelze wird das Fluor an einem Anionenaustauscher adsorbiert. Das bestrahlte Harz wird in5-n Salzsäure eingerührt und zum Quellen gebracht. Nach dem Abfiltrieren wird das aus der, n-Reaktion stammende18F mit einer 0,2% igen Lösung von Dimethyl-dichlorsilan in Xylol extrahiert. In einem aliquoten Anteil der organischen Phase wird es gammaspektrometrisch gemessen. Die Genauigkeit des Verfahrens wurde durch wiederholte Analysen von Standardproben ermittelt und beträgt ±11%. Die Empfindlichkeit wurde zu 0,01g geschätzt.相似文献
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A. A. Ramos S. Ohde M. M. M. Hossain H. Ozaki S. Sirirattanachai J. L. Apurado 《Journal of Radioanalytical and Nuclear Chemistry》2005,266(1):19-29
Summary A systematic and non-destructive technique is proposed for the determination of fluorine in coral samples by instrumental neutron activation analysis using the 19F(n,γ)20F reaction. About 50 to 80-mg samples in polypropylene capsules were irradiated for 15 seconds in the pneumatic transfer tube system (PN-3) of JRR-3M reactor. After the irradiation at a thermal neutron flux of 1.5 . 1013 n . cm-2 . s-1, the coral samples and standards were cooled for 6 seconds and the g-rays emitted were measured for 15 seconds with a Ge detector. The sequence from sample irradiation to g-ray counting was performed under a computer-control mode. The analytical precision was ~5% for the JCp-1 coral standard. The present method was applied to the determination of fluorine in corals from Thailand, Okinawa and the Philippines. The advantage of one method over destructive techniques is discussed by comparing the analytical results obtained for the JCp-1 coral standard using INAA, ion chromatography and spectrophotometry. Factors that may control the levels of fluorine in corals are also discussed. 相似文献
20.
Classical activation analysis of fluorine by thermal neutrons has a limited application because of frequent interference from
chlorine, the short half life20F (11.4 s) and too high dead time of detectors. A procedure is described for fluorine determination using19F (n,p)19O reaction. Use of a boron carbide shield has no effect on the activity of19O (boron ratio −1) but considerably reduces background and interference due to18O (n, γ)19O reaction. The technique has been successfully applied to the determination of fluorine in organic compounds even in the
presence of large amounts of chlorine and oxygen. 相似文献