Determination of fluorine in geological samples using accelerator derived neutrons

A fast, neutron activation analysis technique is described for the determination of fluorine in geological samples. The method utilises the reaction¹⁹F(n,α)¹⁶N for the determination. However, it avoids the interference reaction from oxygen which produces the same radionuclide since the neutrons are derived from the bombardment of beryllium with 3 MeV deuterons. The maximum energy of the neutrons so produced is well below the threshold for the competing oxygen reaction. The results indicate that the method gives acceptable accuracy over the range of a few tens ppm to several percent fluorine content using suitable standards. Sample analysis time is only a few minutes allowing the analyses of large numbers of samples per day.     

Investigation of phase transformations in thermal processing of phosphate rock

The reaction mechanism of the hydrothermal sintering processing of hydroxyfluorapatite (HFA) was studied. Samples from an industrial rotary kiln and laboratory-made samples were investigated by thermal, X-ray and chemical analysis. It was found that HFA decomposes by a solid-solid reaction with Ca-Mg-phosphates and by interaction with fused clinker. Apatite decomposition is not accompanied by fluorine evaporation; it merely creates the main precondition for fluorine evolution from clinker.

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Zusammenfassung Es wurde der Reaktionsmechanismus des hydrothermischen Sinterverfahrens von Hydroxyfluorapatit (HFA) untersucht. Proben aus einem Industriedrehofen und aus dem Labor wurden mittels Thermo-, röntgenographischer und chemischer Analyse untersucht. Es wurde gefunden, da\ HFA durch eine Feststoffreaktion mit Ca-Mg-Phosphaten und mittels einer Wechselwirkung mit geschmolzener Schlacke zerfÄllt. Die Zersetzung von Apatit wird von keiner Abdampfung von Fluor begleitet; es schafft lediglich die Hauptvoraussetzung für die Freisetzung von Fluor aus Schlacke.

     

Use of thermal neutrons to perform clinical analyses in blood and urine samples

Summary In this study we show that the NAA technique can be used to perform clinical analyses of blood and urine, with many advantages towards the conventional methods. From the knowledge of the neutron flux and the induced activity, the concentration ofelements were obtained. In comparison to the conventional techniques, this methodology uses smaller quantities of biological material and allows the simultaneous evaluation of the concentrations of several elements in biological samples at once, something not always possible in the conventional clinical analysis. Another important advantage is that it eliminates the use of standard materials, thus making the analyzing process practical and economic.     

Trace level vanadium determination using thermal lens spectrophotometry

Trace level vanadium determination is reported using a dual beam thermal lens spectrometer. The thermal lens was generated using an argon ion beam laser (pump beam) which was focused into a sample cuvette. The thermal lens signal (TLs) was monitored with a He-Ne laser beam and a photodiode detector. Multichannel averager software was developed for processing the transient TLs. The optimal set up, ensuring maximum sensitivity and linear calibration graphs was obtained using experimental design techniques. Under optimized conditions, the detection limits for aqueous and ethanol-water (2+3 v/v) and (4+1 v/v) vanadium complex solutions were, respectively, 0.0071 mg/l, 0.0065 and 0.0039 mg/l.     

Structure and thermal behaviors of Moroccan phosphate rock (Bengurir)

Moroccan phosphate ores have important phosphate reserves, thus makes possible to distinguish three main layers: submittal, principal and basal. A characterization of the ore was carried out to determine the mineralogical and chemical characteristics. Thermal analysis, infrared and NMR techniques were used to study the thermal and structure behaviors of the organic matter in Moroccan phosphate from Bengurir. The TG analysis showed that the investigated mineral exhibited 7 mass% as total mass loss. The calcination-separation enrichment of carbonate-phosphorite ores from Bengurir region (Morocco) has been studied.     

Analysis of fertilizer phosphates using reactor neutrons and 14 MeV neutrons

Instrumental neutron activation analysis (INAA) in the absolute version was applied to 32 fertilizer phosphates of natural and industrial origin including three standard reference materials (NBS-SRM 120b, BCR-SRM No 32 and No 33). With reactor neutrons 48 elements were determined and with 14 MeV neutrons 3 additional elements were found. The results were used to assess the environmental toxicity of the fertilizers and to characterize their different origins.     

Studies of phosphate anion sorption using the soil samples

The paper presents the results of studies of phosphate anion sorption on various types of soil taken up from the Lublin Province (Poland). Anions belong to the group of ions witch undergo insignificant sorption according to the soil science. As follows from the studies anion sorption depends insignificantly on pH. Sorption isotherms can be described using the Freundlich equation. Sorption extent depends on concentration of iron ions and organic substances in the sample. Specific sorption (chemisorptions) plays the greatest role in the process under investigation.     

Determination of Sc in rock samples by substoichiometric thermal neutron activation analysis

A rapid, selective and simple method has been developed for the determination of Sc in rock samples by thermal neutron activation analysis, employing substoichiometric solvent extraction of Sc(III) with alizarin into 1-octanol. Two samples and a standard can be processed and counted within three hours.     

Novel vanadium phosphate phases as catalysts for selective oxidation

In our effort to induce novel modifications in the structure of some important vanadium phosphate phases used as selective oxidation catalysts, it has been observed that metal ions such as Zn²⁺, Ni²⁺, Pd²⁺can be incorporated into the vanadyl hydrogen phosphate VOHPO₄0.5H₂O phase in very different ways depending upon the medium of preparation. It has been found that the metal ions are either substituted into the lattice with retention of structure of the parent compound or intercalated between the layers of a new mixed-valent phase. These new metal-incorporated phases are catalytically active and the palladium incorporated compound in particular displays shape selective catalysis for different oxidation and reduction reactions. In another approach, the preparation of VOHPO₄0.5H₂O) has been modified to give a novel crystalline phase containing mixed-valentvanadium and having NH₃ species bound to the lattice. This phase could be a potential catalyst for ammoxidation reactions. In addition, novel mesostructured vanadium phosphate phases have been prepared using a long-chain amine as the templating agent involving a ligand templating mechanism of formation.     

Bioimaging of cells and tissues using accelerator-based sources

A variety of techniques exist that provide chemical information in the form of a spatially resolved image: electron microprobe analysis, nuclear microprobe analysis, synchrotron radiation microprobe analysis, secondary ion mass spectrometry, and confocal fluorescence microscopy. Linear (LINAC) and circular (synchrotrons) particle accelerators have been constructed worldwide to provide to the scientific community unprecedented analytical performances. Now, these facilities match at least one of the three analytical features required for the biological field: (1) a sufficient spatial resolution for single cell (< 1 μm) or tissue (<1 mm) analyses, (2) a temporal resolution to follow molecular dynamics, and (3) a sensitivity in the micromolar to nanomolar range, thus allowing true investigations on biological dynamics. Third-generation synchrotrons now offer the opportunity of bioanalytical measurements at nanometer resolutions with incredible sensitivity. Linear accelerators are more specialized in their physical features but may exceed synchrotron performances. All these techniques have become irreplaceable tools for developing knowledge in biology. This review highlights the pros and cons of the most popular techniques that have been implemented on accelerator-based sources to address analytical issues on biological specimens. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Determination of vanadium species in environmental samples

The distribution of vanadium between different oxidation states plays an important role in its environmental chemistry. As its two most commons forms, vanadium(IV) and vanadium(V) have different toxicity, speciation analysis of this element is necessary for environmental and biological samples. This paper presents recent research on the determination of vanadium species. Some important problems concerning stability of vanadium forms and proposed separation techniques are discussed.     

Direct determination of total mercury in phosphate rock using alkaline fusion digestion

The aim of this work was to develop a new method to determine the mercury (Hg) concentrations in phosphate rock using a dedicated analytical instrument (the DMA80 Tricell by Milestone) that employs an integrated sequence of thermal decomposition followed by catalyst conversion, amalgamation and atomic absorption spectrophotometry. However, this instrument underestimates Hg concentrations when phosphorite and apatite rocks are investigated with a classic thermal decomposition treatment that complies with US EPA method 7473.     

A rapid transportation facility for irradiation with thermal and fast neutrons

A rapid vertical transportation system for irradiation with thermal and fast neutrons is devised and partly constructed for inserting samples into the central thimble of our TRIGA MARK II reactor. Fast neutrons will be produced by a⁶LiD-converter, so that the energy distribution of neutrons is hardened by absorption of thermal and by the production of 14 MeV neutrons. In pulse irradiation, the 14 MeV-neutron flux is expected to be in the order of 10¹²/s. The transportation time is to be below 30ms to enable determination of short-lived nuclides down to 15ms. Helium will be used as propelling gas.     

Spectrophotometric method for the determination of vanadium in uranium rich hydrogeochemical samples using pyridyl azo resorcinol (PAR)

A simple and precise method has been developed for the determination of traces of vanadium(V), using 4-(2 pyridyl azo) resorcinol, in natural water samples, containing very high concentrations of uranium. CDTA-pyrophosphate buffer has been used for masking interferants, including uranium which otherwise interferes above 125 ppb. The reaction of vanadium with PAR in the presence of buffer requires a waiting period of 45 min. The Sandell sensitivity of the method is 0.003 microg/ml, at 545 nm at an optimum pH of 6.5 +/- 0.2. The precision of the method is +/- 15% at the 100 ppb level of vanadium(V). The method has been successfully applied to a number of natural water samples during hydrogeochemical exploration.     

Effect of tellurium promoter on vanadium phosphate catalyst for partial oxidation of n-butane

Te-promoted (1%) vanadium phosphate catalyst (VPDTe) was prepared via VOPO4·2H2O by calcining its precursor VOHPO4·0.5H2O in a flow of n-butane/air.VPDTe catalyst has resulted a higher existence of V5+ phase with V5+/V4+ ratio of 0.23.SEM micrographs show that Te addition altered the arrangement of the platelets from "rose-like" clusters to layer with irregular shape.Te addition has also markedly lowered the reduction activation energies of the vanadium phosphate catalyst as revealed by TPR profile.The amount of active oxygen species associated with V4+ phase of the Te promoted catalyst was significantly higher than those of the unpromoted catalyst.These observations suggest that high mobility and availability of reactive oxygen species contributed to the enhancement of n-butane conversion up to 80% at 673 K,while only 47% over unpromoted catalyst (2400 h-1,1.7% n-butane in air).     

Determination of vanadium in ore samples by atomic-absorption spectrophotometry

An atomic-absorption method is described for the determination of vanadium in ores. With a nitrous oxide-acetylene flame and 200 ppm of Al(3+) added to the sample, a sensitivity of 0.2 ppm for 1% absorption can be obtained. Iron above 0.015M interferes but can be extracted into isopropyl ether from 8M hydrochloric acid; the hydrochloric add itself then interferes and must be removed by evaporation.     

Plutonium determination in bioassay samples using radiochemical thermal ionization mass spectrometry

Summary A new high-sensitivity plutonium bioassay program employing thermal ionization mass spectrometry (TIMS) has been developed to monitor Savannah River Site employees for intakes of PuO₂. The U.S. Department of Energy requires bioassay laboratories which have the ability to detect a 100 mRem, 50-year committed effective dose equivalent (CEDE) intake of radioactive material. For PuO₂, traditional alpha-spectrometry methods are not sensitive enough to meet this specification. To comply with this requirement, a radiochemical TIMS method was developed to determine Pu in urine bioassay samples. Four radiochemical separation steps were used to purify Pu from urine to ensure samples were free from matrix effects that interfere with TIMS analysis. These included precipitation, ion-extraction chromatography, electrodeposition, and ion-exchange chromatography. A batch of reagent blanks determined the detection limit for this method was 0.59 fg ²³⁹Pu/l (1.3 µBq ²³⁹Pu/l). The ²³⁹Pu concentration was also measured in 20 urine blank samples to determine the minimum ²³⁹Pu concentration that would indicate an occupational intake. A Probit plot was constructed for the results and the 99 th percentile of the urine blanks showed that the minimum ²³⁹Pu concentration that would indicate an uptake was 2.4 fg/l (5.5 µBq/l).     

Evaluation of botanical reference materials for the determination of vanadium in biological samples

Three botanical reference materials prepared by the National Bureau of Standards have been studied by neutron activation analysis to evaluate their suitability with respect to the determination of vanadium in biological samples. Various decomposition methods were applied in connection with chemical or radiochemical separations, and results for vanadium were compared with those found by purely instrumental neutron activation analysis. Significantly lower results indicate losses or incomplete dissolution, which makes SRM 1575 Pine Needles and SRM 1573 Tomato Leaves less satisfactory than SRM 1570 Spinach. A reference value of 1.15 mg/kg of this material is recommended, based on results from 3 different methods. All three materials are preferable to SRM 1571 Orchard Leaves, while Bowen's Kale remains the material of choice because of its lower concentration.     

Substoichiometric determination of uranium in phosphate rock

The substoichiometric isotope dilution analysis for U(VI) in a synergic extraction system of an excess amount of a chelating agent HHFA and a substoichiometric amount of neutral ligand TOPO has been developed. A constant but substoichiometric amout of U(VI) can be precisely extracted, and U down to ppm levels can be accurately determined by the present method. This method was applied to the analysis of a phosphate rock.