Controle de la purete d'echantillons de nickel par spectrometrie-γ directement apres irradiation au moyen de neutrons thermiques

Purity control of high-purity nickel by direct γ-spectrometry after irradiation with thermal neutronsThe possibilities of analysing high-purity nickel samples by direct γ-spectrometry with a Ge(Li) detector after neutron activation are described. The samples (300—600 mg) are irradiated for 65 h in a thermal neutron flux of 5 X 10¹² n cm^-2 s^-1 and the matrix radioactivity is then allowed to decay for 30 h. It is possible to determine simultaneously 18 elements (the commonest impurities in nickel) by using standards containing known quantities of these elements irradiated under the same experimental conditions. Concentration limits are calculated for 15 elements based on the nuclear characteristics of the radio-isotopes which can be detected by neutron activation. It should be possible to determine 22 elements in nickel samples, at concentrations below 0.1 μg g^-1. The method is suitable for laboratories situated far from irradiation facilities.     

Determination of fluorine in geological materials by fast neutron activation based on the 19F(n,2n)18F reaction

The determination of fluorine in geological materials by fast neutron activation analysis based on the ¹⁹F(n, 2n)¹⁸F reaction is described. Fast neutrons are produced by irradiation of a thick beryllium target with 14.5 MeV deuerons. A rotating smple holder allows simultaneous irradiation of samples and standards. Fluorine-18 is separated by steam distillation of hexafluorosilicic acid or by extraction with triphenylatimony(V) dichloride and the annihilation radiation is measured with γ—γ coincidence equipment. The nuclear interference of recoil protons that induce the ¹⁸O(p,n)¹⁸F reaction is evaluated by means of synthetic samples: for a rock containing 43.4% of oxygen and 0.5% of hydrogen, the interference corresponds to 4.4 μg g^?1 fluorine. The method was applied to USGS and NIMROC reference rocks: for concentrations between 6000 and 50 μg g^?1, the relative standard deviation ranged from 2 to 10%.     

Determination of nickel in standard rocks and glasses by photon activation analysis with 30-MeV bremsstrahlung

The determination of nickel in various silicate rocks and glasses by photon activation analysis with a linear electron accelerator is described. Simultaneous irradiation of the sample and comparative standards produces the ⁵⁸Ni(γ, n)⁵⁷Ni reaction, and a post-irradiation chemical separation is used in conjunction with Ge(Li) γ-spectrometry. Nickel abundances for ten standard silicate rocks and two elementally doped glasses are presented and compared with the data previously published. The method is quite simple and gives good reproducible results for nickel down to sub-p.p.m. levels.     

Activity determination of <Superscript>88</Superscript>Y by means of 4πβ(LS)-γ coincidence counting

The activity concentration of an ⁸⁸Y solution was measured by means of a new custom-built 4πβ(LS)-γ coincidence counting system. Efficiency variation was carried out using chemical quenching and neutral density filters. A relative uncertainty of 0.57% was obtained for the activity concentration. Details of the measurements and of the analysis, as well as possibilities to reduce the uncertainty are discussed. Additional validation measurements were carried out by means of the well-established coincidence counting technique using a proportional counter (PC) in the β channel. The results of both coincidence methods were found to be in excellent agreement.     

Standardisation of a <Superscript>68</Superscript>(Ge+Ga) solution within the CCRI(II)-K2.Ge-68 key comparison

This paper presents the work performed in IFIN-HH, Radionuclide Metrology Laboratory, for the standardization of a ⁶⁸(Ge+Ga) solution, within our participation in the key-comparison codified as CCRI(II)-K2.Ge-68, organised by the CIPM-CCRI(II). Four methods were used: (i) the 4πβ(PC)-γ coincidence method, efficiency extrapolation variant, (ii) the liquid scintillation counting in the variant of triple to double coincidence ratio, (iii) the gamma-ray spectrometry and (iv) the well-type ionisation chamber measurement. The final result was calculated as “power moderate weighted mean” of all results. The results obtained in all methods are presented as relative figures.     

Ni catalysts supported on nano-crystalline aluminum oxide prepared by a microemulsion method for dry reforming reaction

Mesoporous nano-crystalline γ-Al₂O₃ with high surface area prepared by a microemulsion (ME) method was employed as carrier for nickel catalysts in dry reforming of methane for syngas production. The structural properties of the catalysts were characterized by X-ray diffraction, Brunauer–Emmett–Teller surface area analysis, temperature programmed reduction and oxidation and scanning electron microscopy techniques. Microemulsion showed it to be a promising way for the production of nano-crystalline aluminum oxide, and the nickel catalysts prepared with this support have significant features and properties to use in the dry reforming reaction. The results revealed that the prepared γ-Al₂O₃ exhibited a nano-crystalline structure (crystal size: c.4.8 nm) with a high specific surface area (308 m² g^?1). In addition, the catalysts with different nickel contents exhibited high catalytic activity in the dry reforming reaction. The results also showed that an increase in Ni loading from 5 to 15 wt% caused a decrease in the specific surface area and nickel dispersion.     

Determination of gamma-globulin at nanogram levels by its enhancement effect on the resonance light scattering of functionalized HgS nanoparticles

A novel assay of γ-globulin (γ-IgG) with a sensitivity at the nanogram level is proposed based on the measurement of enhanced resonance light-scattering (RLS) signals resulting from the interaction of functionalized nano-HgS with γ-globulin. At pH 5.03, the RLS signals of functionalized nano-HgS were greatly enhanced by γ-globulin in the region of 200-700 nm characterized by the peak around 362 nm. Linear relationship can be established between the enhanced RLS intensity and γ-globulin concentration in the range of 10-140 ng ml⁻¹. The limit of detection is 2.71 ng ml⁻¹. Based on this, a new direct quantitative determination method for γ-globulin in blood serum samples without separation of human serum albumin (HSA) is established. The contents of γ-IgG in blood serum samples were determined with recovery of 95.7-102.5% and R.S.D. of 1.6-2.4%. This method is proved to be very sensitive, rapid, simple and tolerance of most interfering substances.     

Differential perturbed angular correlation measurements of the electric quadrupole interaction of 181Ta IN K3 HfF7

The differential perturbed angular correlation of the ¹⁸¹Ta 133–482 γ-γ cascade was studied in K₃HfF₇. The results indicate a change from a two site model for the ¹⁸¹Ta nuclei at ?196°C to a one site model at 21°C.     

Non-destructive neutron activation determination of silver and antimony in bismuth byγ.γ-coincidence spectrometry

A non-destructive neutron activation method was developed for the determination of silver and antimony in high-purity bismuth ; γ,γ-coincidence counting of ^110mAg or ¹²⁴Sb was applied. The activity of the matrix or other impurities did not interfere. When 1-g samples were irradiated at a neutron flux of 4·10¹¹ n cm^-2 sec^-1 for 25 days, the sensitivity of the method was in the p.p.b. region.     

Multiparameter Coincidence Spectrometry Applied to the Non-Destructive Neutron Activation Analysis of Meteorites

Abstract

A non-destructive method for the neutron activation analysis of chondritic meteorites by multiparameter coincidence spectrometry is described. Results for sodium, cobalt, nickel and iridium are presented, and agree with single coincidence spectrometry measurements. Scandium photopeaks are prominent in the multiparameter spectrum and this element could also be determined. The advantages of multiparameter spectrometry over single coincidence counting are outlined.     

Simultaneous determination of nickel and cobalt traces by neutron activation analysis

Nickel and cobalt traces may be determined by measuring the ⁵⁸Co and ⁶⁰Co activities produced in a nuclear reactor. Solvent extraction of cobalt, and γ-spectrometry on the extracted phase allow a rapid and simple analysis of both metals. The method is applied to the determination of nickel (100–0.2 p.p.m.) and cobalt (0.15–0.001 p.p.m.) in various materials (petroleum, polyphenyls, aluminium).     

Validation of chemical separation method for the determination of 63Ni using TDCR technique in steel samples of APSARA reactor

Activity Standards of ⁶³Ni was used to benchmark our triple-to-double coincidence ratio (TDCR) primary standardization instrument Hidex 300SL TDCR device under different chemical and colour quench conditions. The results were compared with a secondary standardization instrument Tricarb 2910TR that employs transformed spectral index of external standard to assess the quench level of samples. Excellent agreement was observed (within 3 %) for a wide range of standard activity and quench conditions. The method was subsequently used for validating chemical separation procedure for estimation of ⁶³Ni in neutron activated standard nickel and steel samples. Further the method was applied for estimation of ⁶³Ni from decommissioning waste of a research reactor, APSARA.     

Near-infrared spectroscopic determination of human serum albumin, γ-globulin, and glucose in a control serum solution with searching combination moving window partial least squares

Near-infrared (NIR) spectra in the region of 5000-4000 cm⁻¹ with a chemometric method called searching combination moving window partial least squares (SCMWPLS) were employed to determine the concentrations of human serum albumin (HSA), γ-globulin, and glucose contained in the control serum IIB (CS IIB) solutions with various concentrations. SCMWPLS is proposed to search for the optimized combinations of informative regions, which are spectral intervals, considered containing useful information for building partial least squares (PLS) models. The informative regions can easily be found by moving window partial least squares regression (MWPLSR) method. PLS calibration models using the regions obtained by SCMWPLS were developed for HSA, γ-globulin, and glucose. These models showed good prediction with the smallest root mean square error of predictions (RMSEP), the relatively small number of PLS factors, and the highest correlation coefficients among the results achieved by using whole region and MWPLSR methods. The RMSEP values of HSA, γ-globulin, and glucose yielded by SCMWPLS were 0.0303, 0.0327, and 0.0195 g/dl, respectively. These results prove that SCMWPLS can be successfully applied to determine simultaneously the concentrations of HSA, γ-globulin, and glucose in complicated biological fluids such as CS IIB solutions by using NIR spectroscopy.     

Molecular Recognition of Aromatic Nitro Compounds at Cyclodextrin Dithiocarbamate-modified Electrodes

Silver electrodes were modified by the adsorption of α-, β-, and γ-cyclodextrin dithiocarbamates (2α–γ) and characterized by reductive desorption experiments. Their molecular recognition properties were studied by cyclic voltammetry using three families of positional isomers of aromatic nitro compounds. Electrodes modified with 2α and 2β were selective for meta and para isomers while 2γ showed little selectivity. These observations are explained in terms of cavity sizes and guest structure. Computational studies suggest that the main reason for the observed selectivity is the different position of the NO² group in ortho and para isomers with respect to the CD cavity.     

Cyclische α,β-ungesättigte Carbonylverbindungen als Liganden in Nickel(0)-Komplexen

Cyclic α, β-Unsaturated Carbonyl Compounds as Ligands in Nickel (0) Complexes . As a result of the reaction of (Cy₃P)₂Ni(C₂H₄) with p-benzoquinone (p-CH) or maleic anhydride (MSA), nickel(II)-complexes of radical anions are formed which are derived from PCy₃ and p-CH or MSA by an equimolecular coupling. With other cyclic α, β-unsaturated carbonyl compounds (L = 1,4-naphthoquinone, substituted α- and γ-pyrones, substituted coumarins) no comparable reactions proceed in the coordination sphere of nickel(0) phosphine complexes. But depending on the phosphine and on the substrate compounds of the types (R₃P)₂NiL or (R₃P)NiL are obtained. Taking the substituted coumarins for an example, it was demonstrated that the latter type is favoured by bulky phosphines (PCy₃) and by coumarins with a high π-acceptor strength. The i.r. spectra of the complexes (R₃P)NiL are in accordance with an η³(C?C,O)-bridging function of α, β-unsaturated carbonyl ligands and therefore with an oligomeric structure. For the complexes (R₃P)₂NiL and (dipy)NiL an η²(C?C) or a pseudo-η³ (C?C,C) coordination of the ligands is discussed. Of special interest are the compounds (Cy₃P)Ni(DMP) and (Cy₃P)Ni(BDH) (DMP = 2, 6-dimethyl-γ-pyrone, BDH = 2-benzylidene-1, 3-dioxo-hydrindene). Possibly the substituted γ-pyrone is an η⁶-ligand in (Cy₃,P)Ni(DMP). (Cy₃,P)Ni(BDH) is considered to be a nickel(II) chelate of a diva-lent anion which is derived from BDH by the uptake of two electrons. In this connection the limits for a classification of the new complexes as nickel(0) or nickel(II) compounds are mentioned. The polarographic half-wave potentials are applied to an estimation of the reactivity of the α, β-unsaturated carbonyl compounds related to nickel(0) complexes.     

EPR evidence of off-centred nickel at room temperature in NH4Cl

Electron paramagnetic resonance of γ-irradiated ammonium chloride single crystals doped with Ni²⁺ show the formation of Ni⁺ at orthorhombic sites at room temperature. The chlorine hyperfine structure clearly shows that nickel is at an off-centred interstitial position, lending support to the “off-centred impurity ion” model for the recently discovered spontaneous polarization in ammonium chloride.     

Activation analysis of mercury in high purity bismuth

A neutron activation method was developed for the determination of traces of mercury in high purity bismuth. After neutron irradiation at a flux of approx. 4.10¹¹ n/cm²/sec, mercury was separated from the matrix by displacement on metallic copper and subsequent distillation and amalgamation on silver foil. The γ-activity of the ¹⁹⁷Hg was counted in the 68–77 ke V region. The accuracy of the procedure was tested by an addition method of analysis. Bismuth samples with a mercury content in the 10 p.p.b. region were analysed.     

A new functionalized resin and its application in preconcentration system with multivariate optimization for nickel determination in food samples

In this work, Amberlite XAD-2 resin functionalized with 4,5-dihydroxy-1,3-benzenedisulfonic acid was synthesized, characterized and applied as a new packing material for an on-line system to nickel preconcentration. The method is based on the sorption of Ni(II) ions in a minicolumn containing the synthesized resin, posterior desorption using an acid solution and measurement of the nickel by spectrophotometry (PAR method). The optimization of the system was performed using factorial design and Doehlert matrix considering five variables: eluent concentration, PAR solution pH, sample flow rate, PAR solution concentration and sample pH. Signals were measured as peak height by using an instrument software. Using the experimental conditions defined in the optimization, the method allowed nickel determination with achieved sampling rate of 25 samples per hour, detection limit (3 s) of 2 μg l⁻¹ and precision (assessed as the relative standard deviation) of 8.2-2.6%, for nickel solutions of 10.0-200.0 μg l⁻¹ concentration, respectively. The experimental enrichment factor of the proposed system was 46, for 120 s preconcentration time. The proposed procedure was applied for nickel determination in food samples. Recoveries of spike additions (5 or 10 μg g⁻¹) to food samples were quantitative (94-110%).     

Efficient Synthesis of Polycyclic γ-Lactams by Catalytic Carbonylation of Ene-Imines via Nickelacycle Intermediates

The nickel(0)-catalyzed carbonylative cycloaddition of 1,5- and 1,6-ene-imines with carbon monoxide (CO) is reported. Key to this reaction is the efficient regeneration of the catalytically active nickel(0) species from nickel carbonyl complexes such as [Ni(CO)₃L]. A variety of tri- and tetracyclic γ-lactams were thus prepared in excellent yields with 100 % atom efficiency. Preliminary results on asymmetric derivatives promise potential in the synthesis of enantioenriched polycyclic γ-lactams.     

Three-gamma annihilation of ortho-positronium in NiO/γ-Al2O3 catalysts detected by positron lifetime and coincidence Doppler broadening measurements

The pore structure of NiO/γ-Al₂O₃ catalysts is characterized by positron lifetime and Doppler broadening measurements. A very long lifetime τ₄ of 92 ns is resolved from the positron lifetime spectrum measured for pure Al₂O₃, which could be attributed to the ortho-positronium (o-Ps) lifetime in large pores. It was also found that the fitted lifetime τ₄ and its corresponding intensity I₄ obtained from the lifetime spectra both decrease with narrowing energy window of the stop channel in the fast–fast coincidence lifetime measurement system. This suggests that the ultra long lifetime is primarily due to the self annihilation of o-Ps which emits three gamma-rays. Such 3γ annihilation is further evidenced by measuring the Doppler broadening of annihilation gamma rays in coincidence with the prompt gamma rays (1.28 MeV) emitted from the ²²Na positron source. In NiO/γ-Al₂O₃ catalysts both the lifetime τ₄ and its intensity I₄ decreases with increasing NiO content (from 3 wt% to 40 wt%), which indicates decreasing of the number of 3γ events. The 3γ annihilation parameter analyzed from the coincidence Doppler broadening spectrum shows consistent decrease with increasing NiO content.