Neutron scattering by hydrogen in cold neutron prompt gamma-activation analysis

The effects of neutron scattering by hydrogen within targets for cold neutron prompt -ray activation analysis (CNPGAA) have been characterized. For most targets studied, the probability for neutron absorption, and hence CNPGAA sensitivities (counts·s^–1·mg^–1), decrease with increasing H content and with target thickness. Comparisons with results from thermal neutron PGAA indicate that the effects of cold neutron scattering differ from those of thermal neutron scattering. CNPGAA sensitivities for l/v nuclides show similar sensitivity decreases, while Sm sensitivities show smaller decreases.     

On the size variation of the primary solvation sphere of Nd3+ and Tm3+ in mixed system of methanol and water

The stability constants, ₁, of each monochloride complex of Nd(III) and Tm(III) have been determined in the mixed system of methanol and water with 1.0 mol·dm^–1 ionic strength using a solvent extraction technique. The values of ₁ of Nd(III) and Tm(III) increase as the mole fraction of methanol in the mixed solvent system (X _s) increases. However, the variation mode of ₁ againstX _s in the region of 0.00X _s0.40 differs from each other, a concave curve for the Nd(III) and a convex curve for the Tm(III). The LnCl²⁺ formed is present as a solvent-shared ion-pair. Since Cl^– is a structure breaking ion, it was assumed that the primary solvation sphere of Ln³⁺ directly contacted with Cl^–. Calculation of Ln³⁺–Cl^– distance using Bom-type equation revealed the followings: (1) for Tm³⁺ with coordination number 8, the estimated distance between Tm³⁺ and Cl^– increases linearly withX _s in 0.00X _s0.40. The results mean an increase of the primary solvation sphere size of Tm³⁺ withX _s. (2) For Nd³⁺, the distance between Nd³⁺ and Cl^– decreases linearly withX _s in 0.00X _s<0.13, where both coordination numbers of 9 and 8 coexist, while it increases withX _s in 0.13<X _s0.40. The results mean a decrease of the primary solvation-sphere size of Nd³⁺ withX _s in 0.00X _s<0.13 and an increase of that withX _s in 0.13<X _s0.40.     

Large-sample neutron activation analysis: Present status and prospects

Neutron activation analysis is attractive for trace-element determinations in large samples. Facilities for reactor irradiation and -ray spectrometry of kilogram-size cylindrical samples are described. The thermal neutron flux is ca. 5·10¹²m^–2·s^–1 with a _th/ _epi>10⁴, so neutron self-thermalization can be neglected. The correction for the neutron attenuation within the sample is derived from measurement of the neutron flux depression just outside the sample. Correction for -attenuation in the sample is performed via linear attenuation coefficients derived via transmission measurements. Also the natural radioactivity in the sample is taken into account. Examples are given of materials to which large sample INAA has been applied successfully, and further lines of development and exploration are indicated.     

1A1⇔5T2 Spin Transition in Heterometallic Solid Phases FexNi1-x(Htrz)3(NO3)2 · H2O (Htrz = 1,2,4‐Triazole)

Solid phases Fe_xNi_1-x(Htrz)₃(NO₃)₂ · H₂O (0.4 x 0.8$) and Ni(Htrz)₃(NO₃)₂ · H₂O were synthesized and studied. The phases were studied by means of magnetochemistry, powder Xray difraction analysis, and electronic and IR spectroscopy. The heterometallic phases are described by the stoichiographic method of differentiating dissolution (DD). The values of x were determined by two methods — atomic absorption and DD. Magnetochemical data showed that the solid phases exhibit a hightemperature ¹A₁ ⁵T₂ 0.5 x 0.8 and disappears at x = 0.4. The spin transition is accompanied by thermochromism (color changed from pink to white at 0.6 x 1 and from pink to light lilac at x = 0.5). A decrease in x leads to a decrease in the temperature of the forward (under heating T_c ) and reverse (under cooling T_c ) transitions, a decrease in hysteresis value ( T_c), and a smearing of the spin transition.     

Measurements of relative thick target yields for PIGE analysis on light elements in the proton energy interval 2.4–4.2 MeV

In order to extend the energy range of the systematic investigation on relative thick target yields performed by ANTTILA et al² for 1E_p2.4 MeV bombarding energies, gamma spectra and yield data are presented for elements Z=3–9, 11–17, 19–21 in the energy range 2.4E_p4.2 MeV and the results are discussed from the point of view of PIGE analysis.     

Transformations of formaldehyde and glycolaldehyde during the hydroformylation of formaldehyde in the presence of rhodium catalysts

Hydroformylation of formaldehyde to give glycolaldehyde (GA) in the presence of RhCl(PPh₃)₃, RhCl(CO)(PPh₃)₂, or the RhCl₃ + PPh₃ system inN,N-dimethylacetamide was studied. The hydroformylation is accompanied by the Cannizzaro-Tishchenko reaction, condensation of CH₂O with GA to give C₃-C₁₆ polyoxyaldehydes (POA), and dimerization of GA. The formation of POA, which probably occurs through coordination of GA with a Rh atom, predominates among the side reactions. The optimum conditions for hydroformylation of CH₂O were found to be: RhCl₃ + PPh₃ as the catalyst,T 383 K, 12MPa, [H₂O] 1.8 mol L^–1, [Rh] 2.5 · 10^–3 g-at. L^–1, and [CH₂O] 0.03 g L^–1. At a substrate conversion of 62–67 %, the selectivity of GA formation reaches 96 %, and the yield is 60–65 %.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 75–78, January, 1995.     

Chlorine loss from polyvinylchloride under neutron irradiation

PVC samples were irradiated for 1 hour with a thermal neutron flux of _th =4.71·10¹¹n·cm^–2·s^–1 and the chlorine lost during irradiation was measured by -ray spectrometry. About 15% of loss of chlorine has been observed for untreated samples while samples heated to temperatures of 60 and 80°C for one minute before irradiation have been found to loose about 8% and 3%, respectively. The results indicate an influence of the polymer structure on the release of chlorine.     

Interference by neutron induced second order nuclear reaction in activation analysis of platinum group elements after a nickel sulphide fire assay preconcentration

In determining the trace platinum group elements and gold in rocks and ores by the neutron activation analysis after a nickel sulphide fire assay preconcentration, there are interferences due to nuclides produced from second order nuclear reactions. This paper presents the degree of interference calculated over the ranges of long irradiation times and of reactor neutron flux from 1·10¹³ to 1·10¹⁵ n·cm^–2·s^–1. According to the results of these calculations, every one of the second order interfering reactions on the PGE+Au, except the¹⁹⁷Au(n, )¹⁹⁸Au(n, )¹⁹⁹Au reaction, can be neglected under the long irradiation time or high reactor neutron flux. Special attention is given to the interference from gold in the determining platinum.     

Two-dimensional model of a rough surface and spatial distribution of the desorbed species

We consider the angular distribution (AD) of species desorbed from a rough surface described by various distribution functions (DF) of the surface topography. It is shown that the width of the AD of the desorbed flow depends mainly on the roughness coefficient and is almost independent of the DF, except for the indirect dependence through . It is established that the secondary reflection of desorbed species from an uneven surface (with 1.2) has no appreciable effect on the form of the AD. Taking two models as examples, it is shown that anisotropy in the surface topology leads to anisotropy in the AD of the desorbed species.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2699–2704, December, 1990.     

Trace determination of nickel (and cobalt) in biological reference materials by radiochemical neutron activation analysis

Summary Very few biological reference materials are certified for nickel below 1 mg · kg^–1. Neutron activation analysis was only rarely considered as a possible approach; reported sensitivities were usually not very good, unless preconcentration was applied.In the present work, the relatively high fast neutron flux of our TRIGA reactor was used to induce the ⁵⁸Ni(n, p)⁵⁸Co reaction, and ⁵⁸Co (E =811 keV) was radiochemically separated from other radionuclides by classical anion-exchange chromatography in hydrochloric acid. ⁵⁷Co was added to the irradiated sample before decomposition as a radioisotopic yield monitor. By concentrating the final sample fraction and measurement in a well-type HP Ge detector, Ni concentrations down to the 10-g · kg^–1 level could be determined for samples irradiated for 1 day. ⁶⁰Co, produced by neutron capture on ⁵⁹Co, is also coseparated and quantified from the gamma spectrum, so that both elements Ni and Co are determined. Results are reported for a series of NBS and other biological reference materials in the concentration range 10 g-10 mg · kg^–1. Possibilities for further increases in sensitivity are discussed.

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Spurenbestimmung von Nickel (und Cobalt) in biologischen Referenzmaterialien durch radiochemische Neutronenaktivierungsanalyse

     

Effect of annealing on thermal properties and crystalline structure of polyamides. Nylon 12 (polylaurolactam)

Summary Thermal and crystalline behaviour of nylon 12 annealed at low supercooling for 10–2500 hours were studied by DSC, SAXS, WAXS and electron microscopy. The melting temperature and the heat of melting increased on annealing time and temperature from 174 °C and 10 cal/g to 187 °C and 23 cal/g, and at the same time the long period was enhanced from 80 to 160 Å. Long time annealing caused a partial transformation of the-crystal structure to the-crystalline modification.Annealed nylon 12 consisted typical folded chain spherulites of increased latteral dimensions.The extrapolated heat of meltingH _m ^* of the crystalline phase of nylon 12 in the-form is 50 cal/g.With 9 figures     

Metallreiche Phasen im ternären System Ni-Se-Te

Zusammenfassung Die metallreichen Phasen im System Ni-Se-Te wurden durch Röntgenaufnahmen bei Zimmertemp. und bei höheren Temperaturen sowie durchDTA untersucht. Bei Zimmertemp. wurden im pseudo-binären Schnitt Ni₃(Se_1-x , Te _x )₂ Phasen mit den folgenden Strukturen gefunden: rhomboedrischer Ni₃S₂-Typ fürx=0; tetragonaler (Ni,Fe)₁₁Se₈-Typ für 0,15x0,35; tetragonaler Rickardit-Typ für 0,50x0,80; Überstrukturen des Rickardit-Typs für 0,95x1. Bei höheren Temperaturen verbreitert sich das Homogenitätsgebiet der Phase mit der tetragonalen Rickardit-Struktur. Über 600–770°C tritt im ganzen Gebiet 0x1 eine kubisch.

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Metal-rich phases in the ternary system Ni-Se-Te

The metal-rich phases in the system Ni-Se-Te have been studied by X-ray diffraction at room temperature and elevated temperatures, and byDTA. At room temperature phases with the following structures were found in the pseudo-binary section Ni₃(Se_1-x , Te _x )₂: rhombohedral Ni₃S₂ type forx=0; tetragonal (Ni,Fe)₁₁Se₈ type for 0,15x0,35; tetragonal rickardite type for 0,50x0,80; superstructures of the rickardite type for 0,95x1. At higher temperatures the homogeneity range of the phase with the tetragonal rickardite structure broadens. Above 600–770°C a face-centered cubic phase exists in the whole range 0x1; a model for the structure of this phase is proposed. The compound Ni_2,6Te₂ is orthorhombic at room temperature; it becomes hexagonal at 720°C and disproportionates at 820°C; by partial substitution of Te by Se the hexagonal form is stabilized at room temperature. Similarly, the compound Ni₆Se₅ which is stable above 440°C only, is stabilized at room temperature by partial substitution of Se by Te. The phase Ni₆(Se_1-x , Te _x )₅ decomposes by a peritectoid reaction at 650° (x=0) to 590°C (x=0,3).

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Herrn Prof. Dr.H. Nowotny gewidmet.     

Silica Gel Loaded with <Emphasis Type="Italic">o</Emphasis>-Dihydroxybenzene: Design,Metal Sorption Equilibrium Studies and Application to Metal Enrichment Prior to Determination by Flame Atomic Absorption Spectrometry

The aminopropyl silica gel (APSG) prepared by reaction of activated silica gel with 3-aminopropyltriethoxysilane on reaction with 3,4-dihydroxybenzaldehyde has resulted in a new chelating matrix, o-dihydroxybenzene (DHB) anchored silica gel, which is characterized by IR, TGA and elemental analyses. APSG is characterized with ¹³C CPMAS NMR spectroscopy. DHB anchored silica gel sorbs quantitatively (97.4–99.2% recovery) Cu(II), Pb(II), Fe(III), Zn(II), Co(II), Ni(II) and Cd(II) at pH 6.0–7.5, 5.0–7.0, 5.5–7.0, 6.0–8.0, 6.5–8.0, 5.5–7.0 and 6.5–7.5, respectively. The sorption capacity varies from 32 to 348µmolg^–1 and is highest for copper. Desorption was found to be quantitative with 1.0–3.0molL^–1 HCl/HNO₃ (for Pb). The optimum flow rate of the solution for quantitative sorption of metal ions on a column (10cm×10mm) packed with 1g of the modified silica gel is 1.0–4.0mLmin^–1, whereas for desorption it is 2.0 –4.0mLmin^–1. The tolerance limits for NaCl, NaBr, NaI, NaNO₃, Na₂SO₄, Na₃PO₄, humic acid, EDTA, ascorbic acid, citric acid, sodium tartrate, Ca(II) and Mg(II) in the sorption of all the seven metal ions are reported. The preconcentration factors are between 100 and 300 and t_1/2 values 17min. The present matrix coupled with FAAS has been used to enrich and determine the seven metal ions in river and tap water samples (RSD 1.4–7.0%) and in synthetic certified water samples SLRS-4 (NRC, Canada) with an RSD of 2.73–2.83%. The cobalt present in pharmaceutical vitamin tablets and Zn in milk powder was preconcentrated on DHB anchored silica gel and determined by FAAS (RSD of 2.00 to 2.72%).     

Gamma radiolysis of Methyl Red solution and reaction induced by γ-irradiated NaCl in Methyl Red

The -radiolysis of Methyl Red solution in HCl medium at pH=2 has been studied along with energy transfer reaction brought about byF and hole centers of -irradiated NaCl. The G-values for degradation of the azo dye indicator by radiolysis and -irradiated salt were determined as 9·10^–1 and 4.8·10^–3, respectively. The kinetic rate constants (k) of degradation are evaluated as 2·10^–5 rad^–1 in the case of direct radiolysis, while for the irradiated salt it is 2·10^–7 rad^–1. The extent of degradation by direct -radiolysis is 100–200 times greater as compared to that by the -irradiated salt. The same mechanism is proposed for radiolysis as well as the reaction induced by -irradiated sodium chloride.     

Ionization gauge sensitivities of N2, O2, N2O, NO, NO2, NH3, CClF3 and CH3OH

A Bayard-Alpert (BA) gauge was used to determine apparent relative sensitivites S_rel,X for O₂, N₂O, NO, NO₂, NH₃, CClF₃ and CH₃OH from gauge calibration measurements in the range 1.3×10^–1 Pap1.3·10^–3Pa. Nitrogen was used as a calibration standard.     

Lipase-mediated deracemization of secondary 1-phenyl-substituted propargylic alcohols of different topology

Acetylation of (±)-1-phenylnon-2-yn-1-ol, (±)-1-phenylhept-1-yn-3-ol, and (±)-1-phenylundec-4-yn-3-ol ((±)-5) in the presence of lipase from Candida cylindracea (CCL) proceeds slowly to give products with ee 20%. The acetates of these alcohols are hydrolyzed in the presence of porcine pancreatic lipase (PPL) equally unsatisfactorily. The (⁶-arene)tricarbonylchromium complex of alcohol (±)-5 is acetylated in the presence of CCL up to 22% conversion to give (R)-acetate whose oxidative decomplexation followed by saponification results in alcohol (R)-(–)-5 with ee 95%. The configuration of alcohols (–)-5 and (+)-5 was determined by NMR spectroscopy of their esters with (R)- and (S)-Mosher"s acids.     

Synthesis, Formation Mechanism, and Crystal Structure of the Nitrosoruthenium(II) Nitrochloride Complex Fac-K2[RuNO(NO2)2Cl3]

Procedures for synthesis of the first nitrochloride complex of nitrosoruthenium(II), fac-K₂[RuNO(NO₂)₂Cl₃], are described and the mechanism of its formation is suggested. The compound was investigated by IR spectroscopy and X-ray phase and X-ray diffraction analyses. Crystal data for Cl₃N₃O₅K₂Ru: a = 7.050(1), b = 7.524(2), c = 10.125(2) , = 90.44(3), = 103.17(3), = 90.51(3)°, V = 522.9 ³, space group , Z = 2, d _calc = 2.589 g/cm³. The structure consists of the complex anions fac-[RuNO(NO₂)₂Cl₃]^2– and K⁺ cations. The complex crystallizes as triclinic plates and red orange prisms; it is well soluble in water, not readily soluble in KCl solutions, and insoluble in ethanol and acetone; the complex is stable when stored in air.     

Mechanism of the oxidation of L-ascorbic acid by the bis(pyridine-2,6-dicarboxylate)cobaltate(III) ion in aqueous solution

A detailed investigation of the oxidation of L-ascorbic acid (H₂A) by the title complex has been carried out using conventional spectrophotometry at 510 nm, over the ranges: 0.010 [ascorbate] _T 0.045 mol dm^–3, 3.62 pH 5.34, and 12.0 30.0 °C, 0.50 I 1.00 mol dm^–3, and at ionic strength 0.60 mol dm^–3 (NaClO₄). The main reaction products are the bis(pyridine-2,6-dicarboxylate)cobaltate(II) ion and l-dehydroascorbic acid. The reaction rate is dependent on pH and the total ascorbate concentration in a complex manner, i.e., k _obs = (k ₁ K ₁)[ascorbate] _T /(K ₁ + [H⁺]). The second order rate constant, k ₁ [rate constant for the reaction of the cobalt(III) complex and HA^–] at 25.0 °C is 2.31 ± 0.13 mol^–1 dm³ s^–1. H = 30 ± 4 kJ mol^–1 and S = –138 ± 13 J mol^–1 K^–1. K ₁, the dissociation constant for H₂A, was determined as 1.58 × 10^–4 mol dm^–3 at an ionic strength of 0.60 mol dm^–3, while the self exchange rate constant, k ₁₁ for the title complex, was determined as 1.28 × 10^–5 dm³ mol^–1 s^–1. An outer-sphere electron transfer mechanism has been proposed.     

Dissociation equilibrium between uncharged and charged local anesthetic lidocaine in a surface-adsorbed film

The dissociation equilibrium between uncharged local anesthetic lidocaine (LC) and charged local anesthetic LC (LCH⁺) in a surface-adsorbed film was investigated by measuring the surface tension and pH of aqueous solutions of a mixture of hydrochloric acid and LC. The surface tension values decreased slightly with increasing total molality m_t at 0X₂0.5, where X₂ is the mole fraction of LC in the mixture, while they decreased rapidly with increasing m_t at 0.5<X₂1. It was shown from the pH measurements that almost all LC molecules were changed into LCH⁺ ions by protonation at 0X₂0.5 and both forms coexisted only at 0.5<X₂1. The quantities of the respective LC and LCH⁺ transferred from the aqueous solution to the adsorbed film, i.e., their surface densities, were calculated by applying the thermodynamic equations derived to the surface tension and pH data. A greater quantity of LC than LCH⁺ existed in the adsorbed film at the coexisting composition. The partitioning behavior of LC and LCH⁺ in the adsorbed film was characterized by three composition regions: (1) slight partitioning of low surface-active LCH⁺ in the region at 0X₂0.5, (2) preferential partitioning of LC at 0.5<X₂<around 0.7, and (3) negative partitioning of LCH⁺ at around 0.7X₂1. The present results clearly indicate that uncharged local anesthetics transfer into hydrophobic environments such as cell membranes more than charged ones.     

The outersphere complex of EuCl2+ in a mixed system of methanol and water of 1.0M (H, Na) (Cl, ClO4)

The stability constans, ₁, of each monochloride complex of Eu(III) have been determined in the methanol and water mixed system with 1.0 mol·dm^–3 ionic strength using a solvent extraction technique. The values of ₁ increase with an increase in the mole fraction of methanol (X _S ) in the mixed solvent system when 0X _S 0.40. The, distance of Eu³⁺–Cl^– in the mixed solvent system was calculated using the Born-type equation and the Gibbs' free energy derived from ₁. Calculation of the Eu³⁺–Cl^– distance and the preferential solvation, of Eu³⁺ by water proposed the variation of the outersphere complex of EuCl²⁺ as follows: (1) [Eu(H₂O)₉]³⁺Cl^–, [Eu(H₂O)₈]³⁺Cl^– and [Eu(H₂O)₇(CH₃OH)³⁺Cl^– inX _S0.014, (2) [Eu(H₂O)₈]^3–Cl^– and [Eu(H₂O)₇(CH₃OH)]³⁺Cl^– in 0.014<X _S <0.25 and (3) [Eu(H₂O)₇(CH₃OH)]^3–Cl^– and [Eu(H₂O)₆(CH₃OH)[₂ ³⁺Cl^– in 0.25<X _S 0.40.