The determination of uranium and thorium in rocks by neutron activation analysis

A neutron activation method is described for the determination of thorium and uranium in rocks at the microgram and submicrogram levels. Radiochemical separations are carried out using the alpha-active nuclides protactinium-231 and neptunium-237 as tracers. The method is applied to the Standard granite XXX and the standard diabase XXX.     

Simultaneous determination of trace uranium and thorium by radiochemical neutron activation analysis

A method for the simultaneous, radiochemical neutron activation analysis of uranium and thorium at trace levels in biological materials is described, based on a technique known as LICSIR, in which a double neutron irradiation is employed. In the first, long irradiation²³³Pa (27.0 d) is induced by neutron capture on²³²Th and then the sample is cooled for several weeks. A second short irradiation to induce²³⁹U (23.5 m) is followed by a rapid sequential radiochemical separation by solvent extraction of²³⁹U with TBP and²³³Pa with TOPO. Chemical yields of²³⁹U and²³³Pa were measured for each sample aliquot using added²³⁵U and²³¹Pa tracers from the -spectra of the separated fractions. The technique was validated by quality control analyses.     

Determination of uranium and thorium in semiconductor memory materials by high fluence neutron activation analysis

Uranium and thorium were measured by absolute neutron activation analysis in high-purity materials used to manufacture semiconductor memories. The main thrust of the study concerned aluminium and aluminum alloys used as sources for thin film preparation, evaporated metal films, and samples from the Czochralski silicon crystal process. Average levels of U and Th were found for the source alloys to be ≈65 and ≈45 ppb, respectively. Levels of U and Th in silicon samples fell in the range of a few parts per trillion. Evaporated metal films containted about 1 ppb U and Th, but there is some question about these results due to the possibility of contamination. Operated by Union Carbide Corporation for the U.S. Department of Energy, under Contract No. W-7405-eng-26.     

Simultaneous determination of thorium and uranium in ores and SRMs by instrumental neutron activation analysis

A procedure has been developed for the determination of thoirum and uranium in ores and geological materials. The technique is relatively simple, accurate and adaptable routinely. Gamma-ray peak interferences are discussed in detail and the usefulness of the multiple gamma-ray peak ratios in the determination of the purity of peaks has been explained. The precision and accuracy of the method have been determined by analysing IAEA and NBL Standard thorium/uranium ores.     

Determination of uranium and thorium in solar salts by neutron activation analysis

Uranium and thorium contents of solar salts were measured by neutron activation analysis. In advance of neutron irradiation, U and Th were concentrated and separated from some interfering elements by neutralization in which they were precipitated with aluminium hydroxide from solutions obtained by dissolving the salts in water or dilute nitric acid solution. The uranium and thorium concentrations determined were from several hundred ppt to 10 ppb. It was strongly indicated that uranium tends to remain in the solution (brine from seawater) phase in the process of solar salt production while thorium tends to transfer to the solid (solar salt) phase.     

The determination of lead in environmental and geological materials by proton activation analysis

Lead is determined in environmental samples and in rocks using the^206,207,208Pb(p,xn)²⁰⁶Bi reaction. Bismuth is separated by anion exchange or by extraction with antimony diethyldithiocarbamate. Sources of errors such as volatilization of the matrix due to heating during the irradiation, variations of the abundance of the lead isotopes and the standardization were studied in detail. For concentrations between 11 mg/g and 3.7 g/g the relative standard deviation ranges from 2.6 to 5.4%. The detection limit is 10 ng/g.     

Determination of uranium in thorium matrixes by epithermal neutron activation analysis

Uranium in thorium matrixes or in minerals and ores containing thorium is determined by epithermal neutron activation analysis (ENAA). In some minerals and ores, such as monazite sands, the analysis can be carried out by purely instrumental means with no chemical separation of uranium or thorium from the irradiated matrix. For thorium compound matrixes with very low uranium contents, a rapid radiochemical separation method, based on the retention of uranyl ion on anion-exchange resins, is first carried out, before counting the gamma-ray peaks for²³⁹U in multichannel analysers coupled to NaI(Tl) scintillators or to Ge(Li) detectors.     

The determination of vanadium in geological materials by activation analysis with pre-irradiation separation

Vanadium is determined in silicate rocks by neutron activation after dissolution of the samples with HF/HNO₃ and separation by solvent extraction. The chemical yield of the pre-irradiation separation is determined by means of ⁴⁸V tracer. Results for 15 U.S. Geological Survey standard rocks are presented and discussed in relation to literature data. The method is especially useful at vanadium concentrations below 10 ppm, where purely instrumental neutron activation as well as other techniques commonly used for vanadium determinations in rocks, have inadequate sensitivity.     

Non-destructive determination of dysprosium in graphites by neutron activation analysis

Natural graphites, graphite components, spectral and reactor grade graphites have been analyzed non-destructively for dysprosium by neutron activation and γ-spectrometry using^165m Dy (1.2 min) and¹⁶⁵Dy (2.3 hr). In four samples the determined Dy content was in the range 1.48 to 0.039 ppm. The deviation was ±18%. The limit of lower detection of the applied method amounts to 0.01 μg Dy, depending on the background contributed by other impurities.     

Simultaneous determination of uranium and thorium in high grade thorium ores

A routine procedure has been developed for the simultaneous determination of uranium and thorium in high concentration thorium ores. INAA is used to determine the uranium and thorium concentration. However, for very low concentrations of uranium a radiochemical procedure based on the use of NPy/benzene as an extractant has to be employed. The precision and accuracy of the method has been determined by analyzing IAEA and NBL standard thorium/uranium ores.     

A neutron activation analysis procedure for the determination of uranium,thorium and potassium in geologic samples

A neutron activation analysis procedure was developed for the determination of uranium, thorium and potassium in basic and ultrabasic rocks. The three elements are determined in the same 0.5-g sample following a 30-min irradiation in a thermal neutron flux of 2·10¹² n·cm^?2·sec^?1. Following radiochemical separation, the nuclides²³⁹U (T=23.5 m),²³³Th (T=22.2 m) and⁴²K (T=12.36 h) are measured by β-counting. A computer program is used to resolve the decay curves which are complex owing to contamination and the growth of daughter activities. The method was used to determine uranium, throium and potassium in the U. S. Geological Survey standard rocks DTS-1, PCC-1 and BCR-1. For 0.5-g samples the limits of detection for uranium, throium and potassium are 0.7, 1.0 and 10 ppb, respectively.     

Preconcentration and neutron activation analysis of thorium and uranium in natural waters

Uranium and thorium were analyzed in commercial bottled waters and in fresh waters, such as tap water, by neutron activation analysis. The analysis was applied after a preconcentration step from a batch of 1–3 dm³ water under investigation. The adsorption was performed in the presence of a small amount (about 1 g) of an adsorber derived from the salt of a-hydroxyquinoline and benzilic (diphenylglycolic) acid, adsorbed onto charcoal. The preconcentration method has shown to be rapid and reliable. The overall method was set in order to have an alternative method of comparison with other different methods of analysis. The proposed method may be applied to different fresh water samples. This revised version was published online in July 2006 with corrections to the Cover Date.     

Uranium and thorium determination in Brazilian coals by epithermal neutron activation analysis

An experimental technique has been developed to determine impurities in coal. Uranium was determined by counting the²³⁹Np 106.1 keV -ray with a LEPS detector and thorium by counting the²³³Pa 311.8 keV -ray with a Ge(Li) detector. Seventeen coal samples were analyzed with an average precision of 3% and a quantitative determination limit of 0.153 g/g for uranium and 0.078 g/g for thorium. The technique allows determinations of up to twenty elements besides U and Th and can be applied in routine analysis.     

Direct determination of thorium in uranium oxide by X-ray fluorescence

Summary Thorium in uranium is determined directly at trace levels by an XRF method. Uranium oxide samples are put in the form of double layer pellets and analysed by using Philips PW-1220 X-ray spectrometer. The typical value of the precision of the method at 200 ppm level is ±10% and estimation range is 50–1000 ppm of thorium in uranium.

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Direkte Bestimmung von Thorium in Uranoxid durch Röntgenfluorescenz-Spektrometrie

Zusammenfassung Mit Hilfe der beschriebenen Methode kann Th in Spurenkonzentrationen direkt bestimmt werden. Die Uranoxidproben werden als Doppelschicht-Tabletten eingesetzt und mit Hilfe eines Philips PW-1220 Röntgenspektrometers analysiert. Die Genauigkeit im Bereich von 200 ppm beträgt ±10%. Der Anwendungsbereich liegt bei 50–1000 ppm.

     

Non-destructive determination of rhodium in platinum by epithermal reactor neutron activation analysis

Activation in connection with Ge(Li) γ-spectrometry proves profitable in determining traces of rhodium (and silver) in pure platinum. As the 556 keV photopeak of¹⁰⁴Rh was chosen for evaluation, its decay behaviour had to be considered. Moreover, a special automatic correction of dead-time and decay was applied. The limit of detection in a single run was 5 ppm.     

Non-destructive determination of trace elements in tungsten by helium-3 activation analysis

A non-destructive method is described for the determination of trace impurities at sub-p.p.m. levels in a tungsten matrix by 14-MeV ³He activation analysis. A Ge(Li) spectrometer and a multichannel analyzer were used to determine V, Fe, Ni, Zn and Mo impurities. Interfering reactions are discussed in detail.