Determination of chlorine in silicate rocks by neutron activation analysis

A simple radiochemical neutron activation analysis scheme has been developed for the determination of chlorine in silicate rocks. The method involves a 15-min thermal neutron irradiation of rock powder followed by a quick separation of ³⁸Cl as AgCl, and Ge(Li) spectrometry. Chemical yield, normally ranging between 95% and 100%, is monitored gravimetrically through the recovery of AgCl. The procedure has been tested on several geochemical standards to assess its accuracy and precision. The values obtained for standard rocks agree with the literature values. At the 100-ppm level, the analytical precision for chlorine is within ±5% (2σ).     

Determination of silicon in iron by thermal neutron activation

A new chemical separation procedure for the determination of silicon in iron after neutron activation was developed. It uses two separation steps, one on a cation exchange resin in HCl−HF-acetone medium, and the other on alumina at pH 9. The detection limit for silicon was 0.02 μg. This analytical procedure was applied to the control of the zone-melting purification of iron.     

Determination of silicon in metals by thermal neutron activation

A new method of silicon determination in molybdenum by the³⁰Si(n, γ)³¹Si was developed. All the problems occurring during this analysis: standardization, quantitative dissolution, silicon sorption on vessels, reproducibility of β-counting...were carefully studied and new answers were brought to them. The chemical speratation of silicon was performed with a column of anion exchange resin in HCl-HF-H₂O₂ solution and a column of alumina at pH 9. Accuracy and reproducibility were controlled on standard samples prepared by fusion of inactive molybdenum and radioactive silicon in a plasma furnace.     

Investigation of silicon dioxide films by neutron activation analysis and autoradiography

Investigations of insulating silicon dioxide films formed on silicon epitaxial layers are reported. Activation analysis and surface autoradiography were used to determine the concentration distribution and precipitation of contaminants in the internal part of the films and on the surfaces. The aim of this work was to study the origin of the contaminants by sampling each technological product following thermal oxidation, doped oxide deposition, heating and metallizing. Under the given conditions the following detection limits of impurities could be obtained in silicon dioxide films: Na=80 ppb, Sb=100 ppb, Cu=20 ppb and Au=5 ppb.     

Determination of sodium and chlorine in pure water by neutron activation analysis

Neutron activation analysis was applied to determine sodium and chlorine in high purity water samples. After irradiation of the sample,³⁸Cl was purified from⁸²Br and other nuclides by carbon tetrachloride extraction and silver chloride precipitation, and²⁴Na was separated from other alkali elements and other nuclides by adsorption of²⁴Na on HAP. The activities of both elements were measured by conventional G.M. counter. The contamination of the elements from container walls during neutron irradiation and the interference with³⁸Ar(n, p)³⁸Cl reaction on argon dissolved in water were also examined. Water samples containing 3 ppb of chlorine could not be determined accurately, owing to the above mentioned interfering reaction.     

Determination of silicon in aluminium by 14 MeV neutron activation analysis

A method has been developed for determining silicon in aluminium by fast neutron activation. It is based on the separation of two gamma lines by a Ge(Li) detector: the 1.73 MeV line from the product of²⁷Al(n, α)²⁴Na and the 1.78 MeV line from the²⁸Si(n, p)²⁸Al reaction. In the case of aluminium-silicon alloys 100 μg silicon can be determined, with an error of 10% in an aluminium sample of 1 g. This work was supported in part by the International Atomic Energy Agency.     

Determination of silicon in cast iron by 14 MeV neutron activation

Silicon in cast iron was analyzed by 14 MeV neutron activation—high-resolution γ-ray spectrometry. Silicon was detected as²⁸Al, the product of the²⁸Si(n, p)²⁸Al reaction. Interference of⁵⁶Mn was separated using a Ge(Li) detector and a biased amplifying system. The 1. 81 MeV gamma-radiation of⁵⁶Mn, which is the product of the⁵⁶Fe(n, p)⁵⁶Mn reaction of the matrix of cast iron, was used as an internal standard and for correction of the self-absorption of the 1. 78 MeV gamma-radiation of²⁸Al by the sample. The interferences of aluminum, phosphorus and manganese could be neglected according to the results calculated from their nuclear properties and contents in the cast iron of this experiment. The results of this method agreed well with the results of the usual chemical method, with errors less than 5% of the results, and the precision of the method was satisfactory with a C. V. of less than almost 6% for rapid analysis of silicon in cast iron. The analytical line through the origin with a slope of the mean value of the repetition experiments could be used as the analytical line with almost the same precision and accuracy of the results as for the analytical line calculated by the least squares method.     

Determination of phosphorus in semiconductor grade silicon by neutron activation analysis

A method of determination of phosphorus in silicon has been elaborated. The separation of phosphorus is based on the extraction of phosphomolybdic complex in the presence of hold-back carriers of Ta and Au. Contamination factors for various impurities were determined. The lower limit of determination equals 3·10^?11 g P. Types of errors in the determination of concentration profiles are discussed.     

Trace element analyses of spectroscopically pure silicon dioxide by instrumental neutron activation analysis

Spectroscopically pure, 99.999% silicon dioxide (SiO₂) from five different companies was analysed for trace element impurities by instrumental neutron activation analysis using semiconductor detectors and gamma-ray spectrometry. If large amounts of these purified SiO₂ samples are added to, geological samples with low trace element contents e.g., mineral separates such as quartz, feldspar and olivine, the trace element contents of the SiO₂ are a significant contaminant.     

Determination of impurities in semiconductor grade silicon by instrumental neutron activation analysis

Instrumental neutron activation analysis has been applied to semiconductor grade silicon to study the concentration levels of impurity elements, the contamination during the single crystal growing process, and the vertical and radial distributions of impurities, along with the decontamination effect in the analysis. Twenty elements of Au, Br, As, W, Cr, Co, Na, Eu, La, Se, Zn, U, Th, Hf, Fe, Sb, Ag, Ce, Tb and Ta have been analyzed in p- and n-type wafers, single crystals and a polycrystal by a single comparator method using two comparators of gold and cobalt. Considerable surface contamination has been found and could be removed by etching the surface with nitric and hydrofluoric acid before and after irradiation. The impurity concentration has been found to be generally increased in the process of single crystal growth. The vertical and radial distributions of impurities have revealed that some impurity elements were more concentrated in the top region of a single crystal rod than in the middle region, and that Br, Cr, La, Eu and Sb were enriched in the central region and As, U and Fe in the outer region.     

Determination of silicon dioxide in iron and steel-making slags and fluorspars by 14 MeV neutron activation and high-resolution gamma-ray spectrometry

Silicon as silicon dioxide in iron and steel-making slags and fluorspars was analyzed by 14 MeV neutron activation high-resolution γ-ray spectrometry. Silicon was detected by measuring the 1.78 MeV γ-ray of²⁸Al, the product of the²⁸Si(n, p) reaction, using a 30 cm³ coaxial Ge(Li) detector. A modified TPA method was used for the calculation.²⁸Al is also produced from phosphorus by the³¹P(n,α) reaction, and from aluminium by the²⁷Al(n,γ) reaction. The contribution from the former reaction could be corrected experimentally when the P₂O₅ content of the sample was known, while the latter reaction could be neglected in this neutron energy region. The experimental correction coefficient for phosphorus agreed well with the theoretical value calculated from the nuclear properties of silicon and phosphorus. Yields of²⁸Al from SiO₂, P₂O₅ and Al₂O₃ of the same weight percentages were calculated as 1, 0.426 (experimentally 0.44) and 0.0022, respectively. The results of this method agreed well with the results of the usual chemical methods. The limit of detection of SiO₂ in iron and steel-making slags and fluorspars was calculated as 0.07%. The coefficient of variation of repeated experiments was compared with the statistical one.     

Determination of chlorine, bromine and iodine in rock samples by radiochemical neutron activation analysis

Chlorine, bromine and iodine (hereafter, halogens) were detemined for rock samples by radiochemical neutron activation analysis. The powdered samples and reference standards prepared from chemical reagents were simultaneously irradiated for 10 to 30 minutes with or without a cadmium filter in a TRIGA-II reactor at the Institute for Atomic Energy, Rikkyo University. The samples were subjected to radiochemical procedures of halogens immediately after the irradiation. Iodine was firstly precipitated as PdI₂, and chlorine and bromine were successively precipitated as Ag-halides at the same time. In this study, geological standard rocks, sedimentary rocks and meteorites were analyzed for trace halogens. In some Antarctic meteorites, iodine contents were observed to be anomalously high. Chlorine contents also are somewhat high. The overabundance of iodine and chlorine must be caused by terrestrial contamination on the Antarctica.     

Determination of traces of rare earths in high-purity thorium dioxide by neutron activation analysis

The use of thorium dioxide as a nuclear fuel requires the determination of individual rare earth impurities at 0.08–1 mg kg^?1 levels. Neutron activation is sufficiently sensitive but separation from the matrix is essential. In the proposed method, thorium dioxide (5–20 g) is dissolved in concentrated nitric acid with a little hydrofluoric acid; after evaporation, thorium is complexed with ammonium carbonate and the solution is passed through a small column of Chelex-100 resin which retains the rare earths quantitatively without retaining thorium. The rare earth elements are eluted with dilute nitric acid, concentrated, and irradiated with standards; after irradiation the rare earth are collected on a lanthanum carrier and measured by γ-ray spectrometry. The recoveries of rare earths were checked with tracers and by standard addition to thorium dioxide matrices. The reproducibility for La, Eu and Dy was satisfactory at 0.01, 0.003 and 0.002 mg kg^?1, respectively; as was the reproducibility for all rare earths added to thorium dioxide (1–4 μg/5 g). Limits of detection are adequate for certification of nuclear-grade material.     

Determination of silicon,phosphorus and sulfur in alloy steel by neutron activation analysis

Silicon, phosphorus, and sulfur in alloy steel were determined by neutron activation analysis involving rapid radiochemical separation procedures. The standard deviations for silicon, phosphorus, and sulfur were 1.6%, 2.3%, and 2.4% respectively; the sensitivity limits were 3.2, 0.20, and 2.50 p.p.m., respectively. The three constituents could be determined in alloy steel within 2 h of the irradiation.     

Determination of silicon in natural and pollution aerosols by 14-MeV neutron activation analysis

The determination of silicon via the ²⁸Si(n,p)²⁸ Al reaction by means of 14-MeV neutrons is applied to the analysis of pollution and natural aerosols. A Whatman 41 filter (40 cm²) on which airborne particulate material has been collected is compressed into a 3 × 12.7 mm pellet. Standards are prepared in the same way from clean filters spiked with a silicate solution. After a 50-s irradiation and a 75-s decay time, the sample is counted for 2 min with 5” × 5” NaI(Tl) well detector. The 1.779-MeV photopeak of ²⁸Al is measured with a single channel sealer chain or with a multichannel analyser. The reproducibility, sensitivity and liability to interference from other elements were investigated for both counting systems. The homogeneity of the pellets and the filters was checked. The overall precision of one single-channel determination was estimated to be 3.5% after a 24-h high-volume sampling time. Samples collected in urban, industrial and remote areas with concentrations ranging from 0.05 to 15 μg Si m^-3 air were analysed and the results are discussed.     

Determination of rhenium by neutron activation

A neutron activation method is proposed for the determination of rhenium in rocks and ores. After the irradiation, the radiochemical separation consists of a one-step anion exchange; β-activities of radiochemically pure ¹⁸⁸Re or ¹⁸⁶Re are counted. The chemical yield averaged 75% and there was a considerable saving of time in the radiochemical work. Results are quoted for the rhenium contents of the standard rock W-1, several molybdenites and pyrolusites.     

Determination of chlorine dioxide in water by gas chromatography-mass spectrometry

A sensitive gas chromatographic method has been established for the determination of chlorine dioxide in water. With weak basic conditions (pH 9.0), chlorine dioxide reacts with iodide to form iodine, which reacts with 2,6-dialkylphenol to form 4-iodo-2,6-dialkylphenol. The volatile organic derivative was extracted with ethyl acetate, and then measured by gas chromatography-mass spectrometry (GC-MS). The reaction of the active proton of 2,6-dialkylphenols (2,6-dimethylphenol, 2,6-di-isopropylphenol and 2,6-di-tert-butylphenol) with iodine was tested, and compared to each other in terms of reactivity and stability of the derivatives. 2,6-dimethylphenol showed rapid reaction with iodine, and its derivative was stable for 2 weeks. The detection limit of chlorine dioxide in water was about 1.0 ng/mL, and the calibration curve showed good linearity with r2 = 0.998. The existent concentration of chlorine dioxide in water was calculated from multiplying the concentration calculated from the calibration curve of 4-iodo-2,6-dimethylphenol by 0.544. The method was sensitive, reproducible and simple enough to permit the reliable analysis of chlorine dioxide at the low ng/mL level in water.     

Determination of yttrium and lanthanum in zirconium dioxide by HPLC, X-ray fluorescence and neutron activation analyses

Summary Lanthania-and yttria-stabilized zirconium oxide ceramics have been examined using High Performance Liquid Chromatography (HPLC), thermal neutron activation (NA) and X-ray Fluorescence (XRF) analyses and thus determine the stabilizer content. Ceramic powders with the composition ZrO₂:x mol % La₂O₃ (x=5, 10, 15, 20 and 33) and ZrO₂:x mol % Y₂O₃ (x=10, 15, 20 and 25) were prepared by the citrate and the co-precipitation techniques, respectively. The lanthanum content was determined by HPLC (x=5.09, 9.78, 14.98, 19.81 and 25.94) and NA (x=5.15, 10.32, 17.25, 21.08 and 27.97) analyses, the yttrium content by HPLC (x=8.5, 13.5, 17.9 and 22.1) and XRF (x=9.9, 15.8, 20.1 and 24.9) analyses. An experimental sequence, based on continuous dilution of ceramic powder solutions, is proposed for preparing samples for HPLC measurements. A swimming pool nuclear reactor is used for NA analysis. The quantitative determinations of yttrium and lanthanum doping levels obtained using those techniques are described.     

Determination of the elemental distribution in cigarette components and smoke by instrumental neutron activation analysis

Cigarette smoking is a major source of particles released in indoor environments. A comprehensive study of the elemental distribution in cigarettes and cigarette smoke has been completed. Specifically, concentrations of thirty elements have been determined for the components of 15 types of cigarettes. Components include tobacco, ash, butts, filters, and cigarette paper. In addition, particulate matter from mainstream smoke (MS) and sidestream smoke (SS) were analyzed. The technique of elemental determination used in the study is instrumental neutron activation analysis. The results show that certain heavy metals, such as As, Cd, K, Sb and Zn, are released into the MS and SS. These metals may then be part of the health risk of exposure to smoke. Other elements are retained, for the most part, in cigarette ash and butts. The elemental distribution among the cigarette components and smoke changes for different smoking conditions.