Instrumental neutron activation analysis of environmental samples using thek 0-standardization method

The use of thek ₀-standardization method in instrumental neutron activation analysis gives good accuracy and precision. The analysis time can be reduced drastically by employing software for thek ₀-standardization calculations. In this work samples were irradiated in a TRIGA reactor and the gamma spectrum was analysed by Sampo 90 and thek ₀-standardization by the KAYZERO/SOLCOI code (DSM Research). The efficiency measurement and the peak to total ratio at the reference and other geometries were measured and tested for their accuracy by analysing some reference materials. Reference materials such as SRM 1572 (Citrus leaves), SRM 1573 (Tomato leaves), SRM 1575 (Pine needles), IAEA Soil-7 (Soil) and SRM 1646 (Estuarine sediment) were analysed for the major, minor and trace element contents. The results were in good agreement with the certified or literature values. The recently released IAEA 140 (Sea plant homogenates) was also analysed for 28 elements.     

Prompt-gamma activation analysis using thek 0 approach

Applying thek ₀ standardization method to prompt-gamma activation analysis (PGAA) offers similar benefits as in instrumental neutron activation analysis. It has been demonstrated that under constant flux conditionsk ₀-factors obtained by normalizing to a titanium comparator, measured separately, yield consistent analytical sensitivity ratios. The ratio method has been generalized by using stoichiometric compounds for the determination ofk ₀-factors. Since chlorine forms compounds with essentially everyelement and it also serves as a detector efficiency standard,k ₀ values have been determined relative to chlorine as an internal standard for several analytically important elements in two reactor facilities: the thermal guided beam at the BRR in Budapest and the cold-neutron beams at the NBSR at NIST.     

Development and implementation of thek 0-standardization and other parametric methods of INAA in Cuba. Part II

The main results obtained during the characterization of the Triga Mark III reactor at NNRI, Salazar, Mexico, the development of the nonconventional multimonitor HAV-1, the use of Certified Reference Material (CRM) as multimonitor fork ₀-factors experimental determination, and to study the reactor power and slowing-down thickness dependencies of the reactor flux parameters and its influence ink ₀-INAA are presented. The experience of thek ₀-INAA group at ISCTN, in the application of this analytical technique for different purposes is resumed.     

Interacalation of pyridine and its derivatives into crystalline bismuth molybdenum hydrous oxide

The use of thek ₀-standardization method in instrumental neutron activation analysis gives good accuracy and precision. The analysis time can be reduced drastically by employing software for thek ₀-standardization calculations. In this work samples were irradiated in a TRIGA reactor and the gamma spectrum was analysed by Sampo 90 and thek ₀-standardization by the KAYZERO/SOLCOI code (DSM Research). The efficiency measurement and the peak to total ratio at the reference and other geometries were measured and tested for their accuracy by analysing some reference materials. Reference materials such as SRM 1572 (Citrus leaves), SRM 1573 (Tomato leaves), SRM 1575 (Pine needles), IAEA Soil-7 (Soil) and SRM 1646 (Estuarine sediment) were analysed for the major, minor and trace element contents. The results were in good agreement with the certified or literature values. The recently released IAEA 140 (Sea plant homogenates) was also analysed for 28 elements.     

Determination of microelements in thyroids of the inhabitants of Belarus by neutron activation analysis using thek 0-method

The k ₀-method of neutron activation analysis has been tested for applicability to the determination of trace elements in samples of thyroids of inhabitants from regions in Belarus affected to different degree by thyroid cancer among children after the accident of the Chemobyl power plant. It is shown that thek ₀-method produces results identical to the relative method in neutron activation analysis. Significant differences in the elemental composition of thyroids from the regions of Gomel and Minsk are observed and may be related to the different levels of occurrence of thyroid cancer among children.     

Determination of k0- and Q0-factors of short-lived nuclides

k₀- and Q₀-factors of 18 short-lived nuclides used in reactor neutron activation analysis were determined using the Fast Irradiation and Measurement System (FIMS) of the TRIGA MARK II reactor at the Atominstitut der Österreichischen Universitäten. The Q₀-factors were either critically selected from literature, or experimentally determined according to theCd-ratio method, while the k₀-factors were additionally determined by theBare monitor method. A comparison is made with the values calculated by introduction of literature data for the input parameters. Moreover, a user oriented tabulation is presented of k₀-, Q₀-factors and related nuclear data. All results were critically tested with respect to their accuracy and precision.     

The use of the <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-IAEA program in NIRR-1 NAA laboratory

The k ₀-IAEA program developed for implementation of the single comparator instrumental neutron activation analysis method (k ₀-INAA) has been used for elemental analysis with NIRR-1 irradiation and counting facilities. The existing experimental protocols for routine analysis based on the relative method were used to test the capability and reliability of the program for the analyses of geological and biological samples. The Synthetic Multi-element Standards (SMELS) types I, II and III recommended by the international k ₀ user community for the validation of k ₀-NAA method in NAA laboratories, furthermore, the following standard reference materials: NIST-1633b (Coal Fly Ash) and IAEA-336 (Lichen) were analyzed. Results obtained with the version 3.12 of the k ₀-IAEA program were found to be in good agreement with the data obtained with the established relative method using WINSPAN-2004 software. Detection limits for elemental analysis of geological and biological samples with NIRR-1 facilities are provided.     

Determination of <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-values for some elements in neutron capture gamma-ray for prompt gamma activation analysis

Exploration and modification of data for k ₀-PGAA (prompt γ-ray activation analysis) values used as standards for k ₀ standardization are needed. An integrated system has been installed and calibrated in Hot Laboratories Center for PGAA, using ²⁵²Cf isotopic neutron source with neutron flux of 6.16E8 n/cm² s. The prompt k ₀-factors of about 12 elements were determined versus the 1951.1 keV γ-ray of the ³⁵Cl, as well as analyzing crude oil and oil product samples. The concentrations of the elements in crude oil H, B, Mg, Al, Na, Si, P, S, Cl, V and Cd were 1.18E5, 0.084, 5.48E2, 8.45E2 4.88E2, 1.62E2, 3.72E2, 8.2, 144.3, 393 and 209.2 ppm while in oil product samples were 1.32E5, 5.87, 4.56E2, 4.22E2, 7.16E3, 699, 157, 8.74, 492.3, 61 and 198.2 ppm. Validation of the k ₀-PGAA was applied in analyzing standard IAEA reference material (soil-7) which give good agreement with the literature data. The ²⁵²Cf neutron beam in radiation position was characterized by the cadmium-ratio method, and found that the cadmium ratio (f), was 160.     

Carbon-13 kinetic isotope effects in the decarbonylation of liquid formic acid of natural isotopic composition initiated by phosphorus pentoxide

The isotopic composition of the consecutive fractions of carbon monoxide produced in the decarbonylation of liquid formic acid of natural isotopic composition initiated by addition of phosphorus pentoxide has been measured in the temperature interval 19–100°C and the observed gradual decrease of the _PDB values and the increase of thek ₁₂/k ₁₃ ratio of the isotopic specific rate constants (KIE values) for each next fraction of CO have been interpreted in terms of conclusions presented in the first paper from this series¹ concerning the decarbonylation of HCOOH (F.A.) in concentrated and diluted with water phosphoric acid media. The initial fast dehydration of F.A. by phosphoric anhydride, P₂O₅, proceeds at room temperture with about 1% carbon-13 KIE. The (k ₁₂/k ₁₃) values increase with time, as the decarbonylation slows down due to the hydration of phosphorus pentoxide with water generated in dehydration of HCOOH and reach the plateau values characteristic for each reaction temperature. These increasing very slowly with reaction times at intermediate temperatures maximum values of (k ₁₂/k ₁₃) ratios are quite close to values of¹³C KIE observed in the decarbonylation of pure F.A. (k ₁₂/k ₁₃=1.0443 at 81°C). Addition of water to liquid F.A. at 90°C and at 100°C caused the further increase of the¹³C KIE. The detailed discussion of the¹³C KIE in the HCOOH–P₂O₅ system has been given.     

The recommended k0-factors for neutron-induced prompt gamma-ray analysis and the prompt gamma-ray emission probabilities

Recommended k ₀-factors for gamma-lines of 24 elements useful for neutron-induced prompt gamma-ray analysis (PGA) and which are not influenced by neutron spectrum differences were obtained from the k ₀-factors measured with the cold and thermal neutron guided beams of JRR-3M, by statistical calculation. The prompt gamma-ray emission probabilities were derived from the recommended k ₀-factors using atomic weight, isotopic abundance and thermal neutron capture cross section all related to the k ₀-factors, for which one can obtain accurate data. The derived gamma-ray emission probabilities for the light elements (H to Ca) agreed well within ±10% with those of the ENSDF values, which reflect recent data while the agreement for heavy elements (Ti to Pb) was ±40% with those of the ENSDF, which are still composed of old data. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reactor power dependency of the neutron flux parameters fork 0-standardization

Using the facilities of the Triga Mark III reactor at the NNRI, Mexico and the HAV-1 multipurpose monitor, the reactor power dependency for thek ₀-standardization essential neutron flux parameters as: epithermal shape factor (), thermal to epithermal ratio (f) and neutron temperature (T _n ) were experimentally obtained. Evaluation of the obtained dependencies shows that it is unnecessary to analyze the possible introduction of correction factors in thek ₀-INAA experimental results. A single experimental procedure to determine throughf is suggested.     

Magnetic Structures of the Rare-Earth Platinum AluminidesRPtAl (R=Ce, Pr, Nd)

The rare-earth (R) platinum aluminidesRPtAl crystallize in the orthorhombic TiNiSi-type structure (space group Pnma,Z=4), where magnetic rare-earth atoms form a network of chains parallel to thea-axis and parallel to theb-axis. Magnetic structures and phase transitions ofRPtAl (R=Ce, Pr, Nd) compounds were investigated by systematic measurements of magnetic susceptibility, specific heat, and neutron diffraction on polycrystalline samples. The results reveal a large magnetocrystalline anisotropy and magnetic structures that are dominated by a ferromagnetic component parallel to one of the two chain directions: thea-axis for CePtAl and PrPtAl and theb-axis for NdPtAl. The complex magnetism of CePtAl with three successive magnetic phase transitions (T_C=5.9 K,T₂=4.3 K,T₃=2.5 K) and two coexisting propagation vectors (k₁=0 forT≤T_C, k_2i=[0, 0.46, 0] forT₂≤T≤T_C, k₂=[0, 1/2, 0] forT≤T₂) is confirmed to be exceptional amongRPtAl compounds. PrPtAl has a nonmagnetic crystalline-electric field (CEF) ground-state singlet separated by 21 K from the first-excited state CEF singlet and magnetic exchange interactions are strong enough to induce long-range magnetic order (Curie temperatureT_C=5.8 K, propagation vector k₁=0, magnetic group Pnm′a′, ordered saturation momentm₁=1.00(7)μ_B). NdPtAl is a simple ferromagnet (T_C=19.2 K, k₁=0, Pn′ma′,m₁=2.08(4)μ_B).     

The k0-method in cold-neutron prompt gamma-ray activation analysis

The k ₀-standardization method has been applied and evaluated at the cold-neutron prompt gamma-ray activation (PGA) facility of the Swiss spallation source SINQ (Paul Scherrer Institute). The k ₀-factors for 26 elements of interest were measured using chlorine as a comparator. The results showed good agreement with the values determined at other cold and thermal neutron guided beams, except for a few elements. Then, standard reference materials were analyzed to assess the accuracy of the method using the obtained k ₀-factors. Finally, the technique was used for multielement determination in various samples coming from nuclear waste storage, geochemistry and geology. In addition, the non-destructive nature of PGAA offered an interesting application in archeology.     

Determination of total mercury in environmental and biological samples using k0-INAA, RNAA and CVAAS/AFS techniques: Advantages and disadvantages

The accuracy and precision of the results obtained for total mercury in various environmental and biological samples and certified reference materials (CRMs) by various analytical methods, including k ₀-instrumental neutron activation analysis (k ₀-INAA), radiochemical neutron activation analysis (RNAA) and cold vapour atomic absorption (and atomic fluorescence) spectrometry (CVAAS/AFS) used in routine analysis in our laboratory, were investigated. Three natural matrix reference materials (RMs) from the International Atomic Energy Agency (IAEA), five CRMs from the Institute for Reference Materials and Measurements (IRMM), six CRMs from the National Institute of Standards and Technology (NIST) and one from the Jožef Stefan Institute (IJS) were analyzed. The results obtained show good agreement between certified or assigned values, and between the methods used, except for some data obtained by k ₀-INAA in biological samples. This can be explained by losses during irradiation in semi-open systems (irradiation in plastic ampoules) and/or spectral interferences. This revised version was published online in August 2006 with corrections to the Cover Date.     

Experimental determination of k 0 nuclear data for the cesium radionuclides

The current (official) k ₀ nuclear data for the cesium radionuclides was determined circa 1987 and was partially adopted from older literature. In this work we aimed at the redetermination of experimental k ₀, Q ₀ and $\bar{E}$ _r factors with metrological care. The results are in good agreement with more recent results from other authors. Our Q ₀ and $\bar{E}$ _r values were 2–15 and 25 % different, respectively. The k ₀ factors were determined according to the cadmium subtraction technique, resulting in values 3–7 % different than the official ones. Our precision and accuracy is discussed.     

The use of a modified Westcott-formalism in thek o-standardization of NAA: The state of affairs

Recently, the introduction was proposed of the Westcott-formalism in the k_o-standardization method, in order to enable the handling of analytically important non-1/v (n, ) reactions. In the present paper some elucidations are given to the Westcott-basedk _o-method: the black box of Westcott's g+rs formalism is opened; procedures and formulas are given for the experimental determination of the flux parameters and a survey is presented of the status of the nuclear data.     

Spectral moments of polymer graphs

Summary It is shown that for anyk, thekth spectral moment of a polymer graph composed ofn monomer units is an exact linear function of the parametern. This linear relation holds for all values ofn, greater than a critical value ₀=₀(k).on leave from Faculty of Science, University of Kragujevac     

Calculating poly(ethylene-co-acrylic acid)-solvent phase behavior with the SAFT equation of state

Statistical Associating Fluid Theory (SAFT) is used to model the cloud-point behavior of poly(ethylene-co-acrylic acid), with up to 7 mol % acid content, in propane, butane, propylene, butene, and dimethyl ether at temperatures to 250°C and pressure to 2600 bar. The values for the pure component temperature-independent segment volumes, nonspecific interaction energies, and the numbers of segments per molecule are equal to those used for polyethylene, because these copolymers contain modest amounts of acrylic acid repeat units. Two different approaches are used to determine values of the pure component energy of hydrogen bonding, ?/k, and the binary interaction parameter, k_ij. In one approach, ?/k for acid dimerization is obtained from literature spectroscopic data and a constant value of k_ij is fit to each copolymer-solvent cloud-point curve. Increasing the value of k_ij shifts the predicted cloud-point curves to higher temperatures and pressures. For the five solvents used in this study, k_ij decreased steadily in the range of 0.040 to ?0.025 as the acid content in the copolymer increased. The predicted cloud-point curves are in good agreement with experimental data, and the impact of hydrogen bonding on the phase behavior is well represented, even if k_ij is set equal to zero. For the second approach, ?/k is set to ～ 90% of the value obtained from spectroscopic data as determined from a fit of a single poly(ethylene-co-acrylic acid)-butane cloud-point curve, while k_ij is fit to the corresponding polyethylene-solvent system. This approach requires less mixture data than the previous approach, and the calculated cloud-point curves are also in good agreement with experimental data, except for the EAA-DME systems. © 1995 John Wiley & Sons, Inc.     

New prompt k0 and partial cross section values measured in the cold neutron beam of Budapest Research Reactor

Summary A complete series of measurements have been performed in the thermal neutron beam at the Budapest Research Reactor to determine the prompt k₀ factors for every stable element. After the installation of the cold neutron source, the flux of the beam increased by more than an order of magnitude, which made possible to determine the k₀ and cross-section values having low cross-sections with a better accuracy. The paper presents the new data for the first set of low-cross-section elements and they are compared to the best literature data.     

Combining Medium Effects and Cofactor Catalysis: Metal‐Coordinated Synzymes Accelerate Phosphate Transfer by 108

The systematic exploration of the modification of polyethylene imine with guanidinium and octyl groups has led to the identification of a catalyst, CD6, which accelerates the phosphate transfer reaction of HPNP (2‐hydroxypropyl‐4‐nitrophenyl phosphate) in the presence of divalent metals such as Zn²⁺, Co²⁺, Mg²⁺ or Ni²⁺. CD6 exhibits saturation kinetics that are described by Michaelis–Menten parameters K_m ranging from 2.5–8 mM and k_cat ranging from 0.0014–0.09 s^?1. For Zn^II–CD6 this corresponds to an overall acceleration k_cat/k_uncat of 3.8×10⁵ and a catalytic proficiency (k_cat/K_m)/k_uncat of 1.5×10⁸. Catalysis by Zn^II–CD6 is specifically inhibited by inorganic phosphate, allowing turnover regulation by product inhibition. This effect stands in contrast to Zn^II‐catalysed transesterification of HPNP in water or by the synzymes Co^II–CD6 and Ni^II–CD6, with which no such interference by product is observed. These characteristics render synzyme Zn^II–CD6 an efficient enzyme model that reflects enzyme‐like properties in a wide range of features.