Determination of certain trace impurities in uranium concentrates by activation analysis

A method is presented for the simultaneous determination of chromium, iron, cobalt and zinc in samples of uranium concentrates, oxides and metallic uranium by neutron-activation analysis. The method involves adequate decontamination of gross fission product activities by adsorption on silica gel, removal of uranium by solvent extraction, separation of most carrier-free rare-earth activities by coprecipitation with aluminium chloride, and, finally, fractional separation of the elements concerned by ion-exchange chromatography. The method can assay ppm of such elements in limited quantities of samples by scintillation gamma-ray spectrometric analysis with a reproducibility of 10-15%.     

Substoichiometric determination of trace impurities in high-purity materials by radioactivation analysis

The substoichiometric determination of some impurities in gallium arsenide and selenium supplied by OEC and IUPAC, respectively, as reference materials for radioactivation analysis is described.     

On the determination of carbon and oxygen impurities in silicon by3He activation analysis

Carbon and oxygen impurities in silicon have been determined by 7.00 MeV³He activation analysis. The detection limits obtained for interference-free conditions are 0.1 ppb (wt) for carbon and 1.0 ppb (wt) for oxygen in silicon.     

Spectrographic determination of trace impurities in sulphur

Summary An emission spectrographic method for the estimation of traces of some common impurites viz., Al, Ba, Bi, Ca, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sn, Ti and V in high-purity sulphur is described. The impurities separated from 1-g sample, after removing sulphur as SO₂ by heating it in air at about 300° C, were dissolved in a small amount of 6M hydrochloric acid and loaded on 10 mg of carrier mixture containing 90% graphite and 10% sodium chloride in the 1/4 electrode crater. The spectra were exited in a D. C. arc carrying 13 A current for 45 seconds. Cobalt was used as an internal standard and sodium chloride as a carrier. The lowest detection limits lie in the range 0.005 to 0.05 ppm for the different elements. The precision of the method ranges from 6–19% for the elements analysed.

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Zusammenfassung Eine emissionsspektrographische Methode zur Bestimmung üblicher Spuren-Verunreinigungen in hochgereinigtem Schwefel, wie Al, Ba, Bi, Ca, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sn, Ti und V, wurde beschrieben. Die aus 1 g Schwefel, nach dessen Entfernung als SO₂ durch Erhitzen an der Luft bei etwa 300° C, abgetrennten Verunreinigungen werden in wenig 6-m Salzsäure gelöst und mit 10 mg Trägergemisch, bestehend aus 90% Graphitpulver mit 10% Natriumchlorid, in die Vertiefung einer 1/4-Elektrode eingebracht. Das Spektrum wird im Wechselstrombogen von 13 A für 45 sec angeregt. Kobalt dient als interner Standard mit Kochsalz als Träger. Die unterste Nachweisgrenze liegt bei 0,005–0,05 ppm für die verschiedenen angegebenen Elemente. Die Genauigkeit beträgt 6–19%.

     

Trends in optical spectrochemical trace analysis with plasma sources

The state-of-art and trends in the development of optical spectrochemical trace analysis with inductively-coupled plasmas (i.c.p.), direct current plasmas (d.c.p.) and microwave-induced plasmas (m.i.p.) are discussed. Innovation in plasma optical emission spectrometry (o.e.s.) is shown ot lie in new sources such as the low-gas-consumption i.c.p., the air and helium i.c.p. as well as the toroidal m.i.p., which is operated at medium power and possibly with moleculary gases. Sample introduction has been improved by using new pneumatic nebulizers, flow injection, electrotheraml vaporization, hydride generation, direct sample insertion and direct solid sampling. Progress in the acquisition of spectral information is attained by high-resolution spectrometry, Fourier-transform spectrometry and by the use of multichannel detectors. D.c.p./o.e.s. is a mature technique for routin work and m.i.p./o.e.s. is a powerful tool for element-specific detection is chromatography. Plasma sources are also suitable atom reservoirs for atomic fluorescence spectrometry and for laser-enhanced ionization spectrometry. Trends in the figures of merit of optical plasma spectrochemical analysis are discussed.     

Photometric and spectrochemical determination of gold in iron pyrites, copper and lead concentrates

A photometric and a spectrochemical method have been developed for determining gold in iron pyrites, copper and lead concentrates. In both, the sample is dissolved and gold is extracted from 1M hydrochloric add solution with a mixture of ethyl methyl ketone and chloroform (1:1). Gold was determined photometrically with N,N'-tetramethyl-o-tolidine. Conditions have been found for satisfactorily sensitive and reproducible spectral determination of gold. For this purpose the effect of various collectors and buffers on the evaporation curves of gold has been studied, as well as excitation conditions, form of the electrodes, optimum slit-width, and photographic variables. The sensitivity and precision of both methods have been evaluated.     

Some applications of activation analysis for the determination of trace impurities in semiconductor materials

Summary It is shown that activation analysis can be applied with good success for the determination of trace impurities in semiconductor material. The specificity and sensitivity together with a reasonable reproducibility are demonstrated. As an example, a survey of the determinations carried out with Ge, Se and Si matrices is given.

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Einige Anwendungen der Aktivierungsanalyse zur Bestimmung von Spurenverunreinigungen in Halbleiter-Materialien

Zusammenfassung Es wird gezeigt, daß die Aktivierungsanalyse mit gutem Erfolg zur Spurenbestimmung von Verunreinigungen in Halbleiter-Materialien herangezogen werden kann. Spezifität, Empfindlichkeit und Reproduzierbarkeit dieses Verfahrens werden diskutiert. Als Beispiel wird ein Überblick über die Bestimmung der Verunreinigungen in Germanium, Selen und Silicium gegeben.

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Communications given at the meeting Analytisce Probleme der Reindarstellung von Halbleitern 24–25 September 1986, Wiesbaden.     

Substoichiometric determination of trace impurities in zinc selenide

Determination of trace impurities in zinc selenide was carried out by substoichiometric neutron activation analysis. Trace impurities were separated from matrix elements by suitable procedures and determined by substoichiometric methods, i.e., Au was extracted with rhodamine-B, Ag and Cu with dithizone, Cr with sodium diethyldithiocarbamate, Co with 1-nitroso-2-naphthol, and Sb with cupferron. Two sorts of zinc selenide single crystals were supplied for analysis and the following values were obtained as impurity concentration; Au 0.36, 0.076 ppb, Ag 42, 32 ppb, Cr. 1.8, 0.63 ppm, Co 0.16, 0.0079 ppm, Sb 8.5, 5.9 ppb and Cu 1.4, 0.44 ppm. The behavior of copper by heat-treatment of zinc selenide was also studied by means of substoichiometric isotope dilution analysis.     

The effect of iodine in spectrochemical analysis of trace elements in the arc plasma

The addition of iodine increases the spectral-line intensity of elements present in traces in the arc plasma. This increase is particularly significant for elements having high ionization potentials. Besides the effect of iodine on the evaporation from the electrode, iodine exerts a certain effect on processes taking place in the arc plasma. The mechanism of the effect should be primarily related to decreased transport velocities of particles in the presence of iodine.     

Non-destructive activation analysis of trace impurities in germanium

A non-destructive activation analysis of trace impurities in germanium giving rise to long-lived γ-emitting isotopes is described. Hg, Sn, Cr, Sb, Sc, Zn and Co were determined by γ-spectrometry after irradiation with thermal neutrons (φ_th=10^l4n. cm^-2.sec^-1, irrad. time: 15 h, cooling period: ca. 30 days). The complex γ-spectrum was analysed by a combination of Covell's method and matrix calculus. The detection limits are approximately 2 p.p.b. of Hg, 7 p.p.b. of Cr, 200 p.p.b. of Sn, 1 p.p.b. of Sb, 10 p.p.b. of Zn, 0.2 p.p.b. of Co and 0.1 p.p.b. of Sc.     

Substoichiometric and non-destructive determination of trace impurities in high-purity optical glasses by neutron activation analysis

A method of radioactivation analysis has been developed for the determination of 17 elements as impurities in high-purity optical glasses. The substoichiometric extraction of platinum with dithizone was studied and a simple procedure was proposed for the determination of platinum. Copper and manganese were also determined substoichiometrically by the extractions with dithizone and with thenoyltrifluoracetone, respectively. The non-destructive γ-ray spectrometry using a Ge(Li) detector has been applied for the determination of the other 14 elements (Ag, Co, Cr, Eu, Fe, Ir, Sc, Zn, Cs, Hf, Rb, Sb, Ta and Tb). Impurity elements at the ppb level were analysed by the proposed method and it is shown that the method is reliable for the determination of trace impurities in high-purity optical glasses.     

Nondestructive determination of trace impurities in iron by thermal neutron activation analysis with long-lived isotopes

A method is proposed for the instrumental determination of Co, Cu, W, As, Ga and Sb in a pure iron matrix. Semiconductor detectors with high resolving power, automatic data collection and completely computerized data interpretation have been used. A method of preparing and testing composite multi-element standards is described in detail.     

Proton activation analysis of trace impurities in purified cobalt

Nondestructive activation analysis by proton beam bombardment has been applied to cobalt specimens. Thick target yields were measured on 18 elements for the purpose of quantitative analysis. In order to detect precisely the radionuclides with different half-lives, gamma-ray spectrometry was repeated three times after different cooling times of 1, 15 and 250 hrs from the finish of bombardment for 1 hrby 10.4 MeV proton beam. It was found that Ti, Cr, Fe, Ni, Cu, Zn, Ga, Ge, As, Se, Zr, Nb, Mo, Cd, Sn, Sb, and Te of the order of ppm or less could be detected accurately. Using the proton activation analysis developed, the purification effects of anion exchange, electrolytic extraction, and floating zone-refining have been examined. It was confirmed that the concentrations of the impurity elements contained in the starting material decreased stepwise upon the application of each purification method.     

Gas chromatographic analysis of trace impurities in chlorine trifluoride

The gas chromatographic determination of trace gaseous impurities in highly reactive fluorinated gaseous matrices presents unique requirements to both equipment and techniques. Especially problematic are the gases normally present in ambient air namely oxygen and nitrogen. Analysing these gases at the low microl/l (ppm) level requires special equipment and this publication describes a custom-designed system utilising backflush column switching to protect the columns and detectors. A thermal conductivity detector with nickel filaments was used to determine ppm levels of impurities in ClF3.     

The application of organic compounds as thermochemical agents in spectrochemical analysis: The effects of tetraethylammonium iodide in the determination of impurities in materials containing molybdenum

The reducing action of some aliphatic and aromatic hydrocarbon derivatives on the oxides of Me, W, Ti, Zr, Nb and Ta was compared to that of graphite powder. The investigation showed that among the organic compounds studied tetraethylammonium iodide gives a better separation of the volatile elements As, Te, Sn, Pb, Bi, Cd, Ag and In, which commonly occur in the above oxides as impurities, from the molybdenum and better line intensities than when using graphite powder. The possible reduction and iodide forming reactions which take place in the electrode cavity in the presence of tetraethylammonium iodide have been established by using calculated values for the change in the Gibbs free energy and the results of X-ray analyses of sample residues obtained after arcing. This reagent was also found to stabilize the are colunm temperature, a necessary condition for its successful application as a spectroscopic buffer.     

Spectrographic analysis of boron nitride for trace impurities

A d.c. arc emission spectrographic method has been developed for the determination of nine trace impurities in boron nitride. The charge for exciting the sample contains equal quantities of boron nitride and graphite (containing 2% NaF as carrier and 1% La(2)O(3) as an internal standard). The method is useful in the determination of impurities in the range 2-1000 ppm, with a mean relative standard deviation of 13%.     

The spectrochemical determination of indium in cassiterite

In order to determine the indium content of cassiterite specimens, a spectrochemical method, using tin as internal standard and the cathode-layer carbon arc, has been employed. The precision of the procedure is approximately 5 %.     

Determination of trace impurities in palladium by neutron activation analysis

Trace amounts of Ir, Au, Ag, Pt, Zn, Mn, and Cu were determined in high purity palladium by destructive and instrumental neutron activation analysis (NAA). The latter version of NAA was employed for the determination of Ir, Au and Ag. Special attention was paid to a new non-destructive method for the determination of silver traces in palladium. The results obtained by both versions of NAA are critically discussed and compared.