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Abstract  

A method has been developed for routine determination of fluorine in zinc sulfide ores by activation with fast neutrons from a 6.6 Ci227Ac−Be isotope source and counting of the 4.5 to 7 MeV gamma-rays of the product nuclide16N. Samples and standards consist of pellets pressed from a mixture of powdered material with wax or graphite. Samples and standards alternate in a sequence of 20 seconds irradiation, 4 seconds decay and 20 seconds counting. This analysis sequence, including the computation of the analysis results from the counting data automated by means of a LSI-11 Microprocessor with 12K×16 bit memory. The zinc ores, containing 0.3 to 0.7% fluorine have been analysed with a precision ranging from 1.56 to 1.33% relative. As a test for the reliability of the method, three standard reference materials were analysed in the same way as the zinc ore samples.

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Abstract  

The eight segments of five normal human livers are analysed for 25 trace elements by radiochemical NAA. This consits of an automated wet destruction of the samples and two distillations, followed by ion exchange procedures. Ru is used as triple-comparator for the standardisation. Short-lived and matrix-isotopes are standardised by the Bowen's kale powder. The results reveal that the coefficient of variation within the liver is smaller than 10% for the elements Cd, Cl, Cs, Cu, Fe, K, Mg, Mn, Rb, Se and Zn. The highest range observed for the elements As, Br, Co, Cr, Hg, La, Mo, Na and Sb within a liver is smaller than the range observed between the five livers.

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Abstract  

A method has been developed to routinely analyse managanese ores and ferro-manganese, by neutron activation making use of a cylindrical 1 Ci226Ra−Be source. A description of the source, the moderator and the pneumatic irradiation facility is given. The irradiation position has been optimized for minimum flux gradients and maximum reproducibility. Samples and standards consist of pellets pressed from a mixture of powdered material and graphite weighing approximately 5 g. Samples and standards alternatively go through a sequence of 20 min irradiation, 20 min decay, and 20 min counting. Pyrolusites containing from 30 to 55% Mn and ferro-manganese containing approximately 80% Mn have been analysed with a precision of 0.1% absolute.

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Abstract  

A non-destructive method has been developed for the precise and accurate determination of Sn in cassiterite ores. Irradiation is performed by means of a 6.6 Ci227Ac−BE isotopic neutron source with a total neutron output of 108 n·sec−1. Samples are pellets pressed from a mixture of cassiterite powder and wax as a binding material. With a 4 hrs analysis time and a relative precision of 0.45%, the new method is faster and at least as precise as any existing destructive chemical method. The accuracy is proved to be better than that of the commonly used iodimetric titration method.

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Abstract  

A comparison has been made between flux density distributions from massive and ring-shaped cylindrical isotopic neutron sources. A considerable gain in direct fast neutron flux is obtained for the latter geometry as well as a neat separation of fast and thermal flux density maxima along the axis of the source. Applications of these favourable properties are discussed.

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Abstract  

The average cross-section in a fission-type reactor spectrum was determined experimentally for the reactions:46Ti(n,p)46Sc,47Ti(n,p)47Sc,48Ti(n,p)48Ti(n,α)45Ca and50Ti(n,α)47Ca. In order to obtain the (n,p) cross-sections, reactor irradiation of titanium was followed by measurement of the induced scandium activities with a Ge(Li) detector of calibrated detection efficiency. For this no chemical separations had to be carried out. For the (n,α) reactions, however, the induced calcium activities were separeted and purified by oxalate precipitation, after the bulk of the radioactivity had been removed by precipitation of titanium hydroxide. The47Ca disintegration rate was determined in the same way as for the scandium isotopes, whereas for45Ca liquid scintillation counting was carried out. The shape of the reactor spectrum was investigated by irradiating reference threshold detectors with different effective threshold energies. To correct for (n,γ) interferences, irradiations were carried out with and without cadmium shielding. On the basis of
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\bar \sigma _F = 0.64$$ \end{document}
mb for the reaction27Al(n,α)24Na, the average cross-sections were as follows:46Ti(n,p)46Sc:10.5±0.4 mb;47Ti(n,p)47Sc: 16.3±0.6 mb;48Ti(n,p)48Sc:0.272±0.005 mb;48Ti(n,α)45Ca: 34μb;50Ti(n,α)47Ca: 8.1±0.3 μb.
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Abstract  

Isotopic abundance values for50Cr,58Fe and109Ag and the absolute gamma-intensities for51Cr,59Fe and110mAg were evaluated. These evaluated data, together with experimental k0-determinations (i.e. from the
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\begin{gathered} {}^{5 0}Cr(n,\gamma )^{5 1} Cr; \sigma _0 = (15.2 \pm 0.2) barn [cf.:15.8 - 16.0] \hfill \\ {}^{5 8}Fe(n,\gamma )^{5 9} Fe; \sigma _0 = (1.31 \pm 0.03) barn [cf.:1.14 - 1.16] \hfill \\ {}^{1 0 9}Ag(n,\gamma )^{1 1 0 m} Ag;\sigma _0 = (3.89 \pm 0.05) barn [cf.:4.4 - 5.0] \hfill \\ \end{gathered}$$ \end{document}
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Abstract  

Cadmium, thallium and lead are determined in environmental samples using the111,112,113Cd(p,xn)111In,203Tl(p,3n)201Pb and206,207,208Pb(p,xn)206Bi reactions.111In.201Pb and206Bi are chemically separated by anion exchange and anodic deposition of lead(IV). oxide. Detection limits are 6, 44 and 25 ng/g for cadmium, thallium and lead, respectively. The results obtained for certified reference materials are in good agreement with the certified values.

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Abstract  

The present paper deals with the accuracy and applicability of the k0-standardization technique in NAA. Topics included are: user-oriented outline of the method, relevant nuclear data (k0, Q0, tc.), the non-1/E epithermal flux distribution, small detector separations and/or extended source geometries, (n, ) reactions with a Westcott-g1, primary interferences, subsequent (interrupted) irradiations, the non-constancy of the neutron flux during irradiation, and a final account of the accuracy. Although the paper is written in terms of the k0-methodology, a good deal of the considerations can be transferred to most types of single-comparator standardization.

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Abstract  

Neutron activation analysis was applied to the determination of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Yb, Lu and Th in rare-earth concentrates resulting from minerals. High-resolution gamma-ray spectrometry with a Ge(Li) detector was used for the non-destructive determination, and a single comparator method using Co as flux monitor was applied.

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