Performance evaluation of k 0-instrumental neutron activation analysis and flame atomic absorption spectrophotometry in the characterization of various types of alloys

Certified alloys of Ni–Cu based, Fe based and Cu–Sn based were analysed by semi-absolute, standardless k ₀-instrumental neutron activation analysis (k ₀-INAA) and flame atomic absorption spectrophotometry (FAAS) aiming at evaluating their comparative performances. In k ₀-INAA measurements, the irradiations were performed at miniaturized neutron source reactor having thermal neutron flux of about 1 × 10¹² cm^?2 s^?1. The experimentally optimized parameters for INAA suggested a maximum of three irradiations for the quantification of 21 elements within 5 days. The same experiments also produced quantitative results of 13 elements not reported in the certificates of the reference materials. AAS was, however, unable to determine any of those elements. Accuracy of the two techniques was assessed by comparing their average root mean squared errors. The data analysis concluded that k ₀-INAA had better sensitivity and accuracy than FAAS.     

Characterization of pneumatic fast transfer system irradiation position of KAMINI reactor for k 0-based NAA

The pneumatic fast transfer system position at KAMINI reactor, Indira Gandhi Centre for Atomic Research, India was characterized by determining the epithermal neutron flux shape factor (α) and the sub-cadmium to epithermal neutron flux ratio (f) for k ₀-based Neutron Activation Analysis (k ₀-NAA). For determination of α value, bare, Cd-ratio and Cd-cover methods were employed using dual and multi monitors namely Au, Zr and Zn. For calculation of f, Au and Zr monitors were used in the case of bare method and Au monitor was used for cadmium ratio and cadmium cover methods. The determined α-value of PFTS indicated a hard epithermal neutron spectrum and the f value indicated about 96 % thermal neutron component. For validation of k ₀-NAA method, reference materials namely NIST SRM 1646a (Estuarine Sediment) and BCS Nb-stabilized Stainless Steel (BCS/SS No.261/1) were analyzed. The percentage errors of the determined concentration values of elements were within ±5 % with respect to the certified values and the Z-score values at 95 % confidence level were within ±2 in most of the cases.     

Implementation of the k 0-standardization method for analysis of geological samples at the Neutron Activation Analysis Laboratory, São Paulo, Brazil

The Neutron Activation Analysis Laboratory (LAN-IPEN) has been analysing geological samples for many years with the INAA comparative method, for geochemical and environmental research. This study presents the results obtained in the implementation of the k ₀-standardization method at LAN-IPEN, for geological samples analysis, by using the program k ₀-IAEA, provided by the International Atomic Energy Agency (IAEA). The thermal to epithermal flux ratio f and the shape factor α of the epithermal flux distribution of the IEA-R1 nuclear reactor of IPEN were determined for the pneumatic irradiation facility and one selected irradiation position, for short and long irradiations, respectively. To obtain these factors, the “bare triple-monitor” method with ¹⁹⁷Au–⁹⁶Zr–⁹⁴Zr was used. In order to validate the methodology, the geological reference materials basalts JB-1 (GSJ) and BE-N (IWG-GIT), andesite AGV-1 (USGS), granite GS-N (ANRT), SOIL-7 (IAEA) and sediment Buffalo River Sediment (NIST–BRS-8704), which represent different geological matrices, were analysed. The concentration results obtained agreed with assigned, with bias <10 % except for Zn in AGV-1. The U-score test showed that all results, except Mg in JB-1, are within 95 % confidence interval. These results indicate excellent possibilities of using this parametric method at the LAN-IPEN for geochemical and environmental studies.     

k 0-INAA of biological matrices at IPEN neutron activation analysis laboratory,São Paulo,using the k0_IAEA software

This study presents the results obtained in the application of the k ₀-standardization method at the Neutron Activation Analysis Laboratory at IPEN (LAN-IPEN), for biological sample analysis, by using the k0_IAEA software, provided by the International Atomic Energy Agency (IAEA). The thermal to epithermal flux ratio f and the shape factor α of the epithermal flux distribution of the IEA-R1 nuclear reactor of IPEN were determined for the pneumatic irradiation facility and one selected irradiation position, for short and long irradiations, respectively. To obtain these factors, the “bare triple-monitor” method with ¹⁹⁷Au–⁹⁶Zr–⁹⁴Zr was used. To evaluate the accuracy of the results, bias (%) and E _n-number test were applied to the results obtained in the analysis of the biological reference materials NIST SRM 1547 peach leaves, INCT-MPH-2 mixed polish herbs and NIST SRM 1573a tomato leaves. Bias (%), for most elements, ranged from 0 to 30 %, in relation to certified values. E _n-number values showed that, with few exceptions (Na in NIST SRM 1547 and NIST SRM 1573a, and Al, Cr, Sc and Zn in INCT-MPH-2), the results were within a 95 % CI. These results pointed to the possibility of using the k ₀-INAA method with the k0_IAEA software for analysis of biological samples at LAN-IPEN.     

Neutron flux characterization of the Moroccan Triga Mark II research reactor and validation of the k 0 standardization method of NAA using k 0-IAEA program

The aim of this work was to implement and to validate the k ₀ standardization method in neutron activation analysis (k ₀-NAA) at the Moroccan TRIGA Mark II research reactor. This technique was used in order to determine, the calibration of several HPGe detectors and calibration of neutron flux parameters in the typical irradiation channels [rotary specimen rack (RSR) and the pneumatic tube system (PTS) facilities]. Calibrations and calculations of k ₀-NAA results were carried out using the k ₀-IAEA program. The two parameters of neutron flux in the selected irradiation channels used for elemental concentration calculation, f (thermal-to-epithermal ratio) and α (deviation from the 1/E distribution), have been determined as well in the PTS as in the RSR facilities using the zirconium bare triple method. Results obtained for f and α in two irradiation channels show that f parameter determined in this way is different in the RSR and the PTS facilities. This can be explained by the fact that the RSR channel is situated in a graphite reflector and is relatively far from the reactor core, while the PTS is in the core. Five reference materials of different origin obtained from USGS (basalt BE-N, bauxite BX-N, biotite mica-Fe, granite GS-N) and IAEA (Soil-7) were used to evaluate the validity of this method in our laboratory by analyzing the elemental concentrations with respect to the certified values. In general, good agreement was obtained between results of this work and values in certificates of the individual reference materials, thus proving the accuracy of our results and successful implementation of the method for analysis of real samples.     

Determination and evaluation of fission k0-factors for correctionof the 235U(n,f) interference in k0-NAA

In order to provide a tailored solution for the correction of the ²³⁵U interference in k₀-NAA, fission k₀-factors for the analytically relevant radionuclides/gamma-lines (versus gold as the comparator), are experimentally determined in four channels of the Gent THETIS reactor. A comparison is made with former data from the literature. The new evaluated results are to be implemented in the forthcoming upgrade of the DSMKayzero software package for k₀-NAA.     

Large sample neutron activation analysis of dross for gold and silver

Large sample neutron activation analysis of dross from India Government Mint, Mumbai was carried out for quantification of gold (Au) and silver (Ag) using graphite reflector position of Advanced Heavy Water Reactor critical facility at Bhabha Atomic Research Centre, Mumbai. The k ₀-based internal monostandard NAA was used to calculate concentration ratios of Au and Ag with respect to sodium (Na), which was used as an internal monostandard. The concentration ratio values of Au to Na of varying mass of dross showed that mass ≥2 g was the representative sample size for analysis. Concentrations of gold and silver were found to be in the range of 200–400 and 1200–1700 mg kg^?1, respectively in three different samples.     

Application of the <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-NAA method at the HANARO research reactor

The k ₀-standardization method (k ₀-NAA) is known as one of the most remarkable progresses of the NAA with its many advantages. For the application of k ₀-NAA method at the NAA #1 irradiation position where the neutrons are well thermalized in the HANARO research reactor, KAERI, Korea, the determination of the reactor neutron spectrum parameters such as α and f have been carried out. The measured values of α and f using the “Cd-ratio” triple monitor method were 0.127±0.022 and 1010±70, respectively. To evaluate the applicability of k ₀-NAA in our analytical system, the analysis of three kinds of SRMs was executed. The analytical results showed that the relative error of most of the elements was less than 10% and the U-scores were within 2. It is turned out that the procedure of the k ₀-NAA in the HANARO research reactor is available for a practical application in the environmental fields.     

Establishment of the k 0, \bar{E}_{\rm r}, Q 0, and cascade coincidence correction factors for the determination of 129I by k 0-NAA

A k ₀-NAA procedure used in the determination of ¹²⁹I is established. For this purpose, the k ₀-values for the reaction ¹²⁹I (n, ??) ¹³⁰I are determined, the Q ₀- and $\bar{E}_{\rm r}$ -values are calculated, and the correction procedure for the cascade coincidence effects is established by calculation of the correction factor COI for five ¹³⁰I ??-rays (418.0, 536.1, 668.5, 739.5, and 1157.5 keV).     

k 0-RNAA used in determination of 129I in a mixed resin sample

A k ₀-RNAA procedure was developed to determine ¹²⁹I in a mixed resin sample. CH₄ extraction and (NH₄)₂SO₃ back-extraction were used to separate ¹²⁹I in ashed samples. The ¹²⁹I target sample for irradiation in the reactor was prepared by heating the (NH₄)₂SO₃ back-extraction solution to reduce its volume and then to dry it in a quartz ampoule. No MgO and LiOH were needed during the target sample preparation. After irradiation, the nuclide ¹³⁰I was purified by combining hydrated antimony pentoxide column and CH₄ extraction separations. A k-factor was determined for the reaction of ¹²⁷I (n, 2n) ¹²⁶I and used for iodine chemical yield determination. The apparent ¹²⁹I concentrations of five nuclear reaction interferences were calculated. The relative standard deviation of three ¹²⁹I determinations was found to be 3.5 %. The ¹²⁹I content in the analyzed resin was found to be 1.36 × 10^?9 g/g (8.63 × 10^?3 Bq/g) with a relative uncertainty of 9.1 %. The detection limit of ¹²⁹I was calculated to be 7.4 × 10^?13 g (4.7 × 10^?6 Bq) in a k ₀-RNAA of a blank sample.     

Applications of k 0 NAA at FRM II with high f values

The research reactor FRM II offers different irradiation facilities with highly thermalized neutron flux. 3 facilities for the k ₀ neutron activation analysis (k ₀ NAA) will be introduced shortly. The influence of flux parameter α on the concentration calculation of samples irradiated in a neutron field with very high ratio of thermal to epi-thermal neutron flux f > 1,000 are here investigated. Even for the most k ₀ isotopes with big Q ₀ values, the uncertainty of a concentration calculation without α correction is <3 %, when the f value larger than 3,000. The uncertainty is about 5 % for the isotope ⁹⁶Zr in this case. The k ₀ library of the computer program MULTINAA is updated. A standard reference material IAEA/soil-7 was analyzed to verify the k ₀ NAA at FRM II.     

Determination of thermal to epithermal neutron flux ratio (f), epithermal neutron flux shape factor (α) and comparator factor (F<Subscript>c</Subscript>) in the Triga Mark II reactor,Malaysia

The thermal to epithermal neutron flux ratio (f or Ø _th /Ø _e ), epithermal neutron flux shape factor (α) and comparator factor (F _c ) are essential parameters when calculating the concentration of sample using k ₀-standardization method in the neutron activation analysis (NAA). The work was performed in the Triga Mark II reactor of Malaysian Institute for Nuclear Technology Research (MINT) using Au/Zr monitor couple. Twenty channels in the reactor have been evaluated and the corresponding thermal to epithermal neutron flux ratios (f) ranged from 11.69 to 47.89. The epithermal neutron flux shape factors (α) were found in the range of ?1.50·10^?1 to 1.59·10^?1 and the comparator factors (F _c ) were calculated within the range of 9.85·10³ to 6.70·10⁴. These results allowed us to study the neutron flux distribution more precisely and established the goodness of fit for k ₀-NAA.     

The application and development of k0-standardization method of neutron activation analysis at Dalat research reactor

In recent years the k ₀-NAA method has been applied and developed at the 500 kW Dalat research reactor, which includes (1) the establishment of a PC database of k ₀-NAA-related nuclear parameters, e.g., radionuclide produced, half-lives, k ₀-factors, Q ₀, _r, E _g, etc; the access to the database is able by a k ₀-NAA software or by manual; (2) the detection efficiency calibration of gamma spectrometers used in k ₀-NAA, (3) the determination of reactor neutron spectrum parameters such as a and f factors and neutron fluxes in the irradiation channels, and (4) the validation of the developed k ₀-NAA procedure by analysing some SRMs, namely Coal Fly Ash (NIST-1633b), Bovine Liver (NIST-1577b) and IAEA-Soil7. The analytical results showed the deviations between experimental and certified values were mostly less than 15% with most Z-scores lower than 2. The k ₀-NAA procedure established at the Dalat research reactor has been regarded as a reliable standardization method of NAA and as available for practical applications, in particularly for airborne particulate and crude oil samples.     

Trace and essential elements determination in baby formulas milk by INAA and k 0-INAA techniques

As a part of the food analysis program executed at Es-Salam research reactor by neutron activation analysis laboratory, the concentration of As, Ba, Br, Ca, Fe, K, La, Rb and Zn in baby formulas milk have been determined by using INAA and k ₀-NAA techniques. It was found that the concentration of all elements obtained by both techniques was relatively identical for the three brands of the 0–6 and 6–12 months of analyzed samples. In addition, the analytical results have been compared with those given by producers.     

Determination of neutron flux parameters in PUSPATI TRIGA Mark II Research Reactor, Malaysia

In standardization NAA, it is necessary to characterize the neutron spectrum parameters such as epithermal neutron flux shape factor (α), thermal to epithermal neutron flux ratio (f), thermal neutron flux (φ _th) and epithermal neutron flux (φ _epi) in the irradiation facility to determine the concentration of an element in the sample using absolute and k ₀ standardization methods. The α and f were determined using Cd-ratio multi monitor method using experimental data obtained in PUSPATI TRIGA Mark II research reactor at four irradiation positions (10, 20, 30 and 40) of the rotary rack. The calculated values of α and f ranged from 0.006 to 0.0281 and 18.56 to 19.12 respectively. The average values of φ _th and φ _epi were found as 2.33 × 10¹² and 1.23 × 10¹¹ n cm^?2 s^?1 respectively. Moreover, a comparison of the neutron flux parameters in the present study shows an acceptable level of consistency with those of previous studies.     

Determination of the k 0-values for 75Se, 110mAg, 115Cd–115mIn, 131Ba, and 153Sm by irradiation in highly thermalized neutron flux

The k ₀-values were determined for five high Q ₀(n,γ) reactions, including ⁷⁴Se(n,γ) ⁷⁵Se, ¹⁰⁹Ag(n,γ) ^110mAg, ¹¹⁴Cd(n,γ) ¹¹⁵Cd–^115mIn, ¹³⁰Ba(n,γ) ¹³¹Ba, and ¹⁵²Sm(n,γ) ¹⁵³Sm. These determinations were carried out under favorable experiment conditions: the irradiations were performed in a highly thermalized neutron flux, the irradiated target samples were counted at a far distance from HPGe detector with an efficiency carefully calibrated, and the k ₀-values were calculated against an internal comparator. When compared to the new values from this work, the 2003 recommended ^110mAg k ₀-values are confirmed. The other confirmed recommended k ₀-value is that of ⁷⁵Se 400.7 keV line. However, for the other ⁷⁵Se γ-lines, the new k ₀-values are 4–10 % higher. It is assumed that an inaccurate efficiency calibration was used when the recommended k ₀-values were measured. For the other three nuclides, the new k ₀-values are higher by 4 % for the ¹¹⁵Cd–^115mIn γ-lines, lower by 6–8 % for the ¹³¹Ba γ-lines, and lower by 8.8 % for the ¹⁵³Sm 103.2 keV γ-line.     

Purification, Characterization, and Specificity Determination of a New Serine Protease Secreted by Penicillium waksmanii

The purpose of this work was to purify a protease from Penicillium waksmanii and to determine its biochemical characteristics and specificity. The extracellular protease isolated that was produced by P. waksmanii is a serine protease that is essential for the reproduction and growth of the fungus. The protease isolated showed 32 kDa, and has optimal activity at pH 8.0 and 35 °C towards the substrate Abz-KLRSSKQ-EDDnp. The protease is active in the presence of CaCl₂, KCl, and BaCl, and partially inhibited by CuCl₂, CoCl₂ and totally inhibited by AlCl₃ and LiCl. In the presence of 1 M urea, the protease remains 50 % active. The activity of the protease increases 60 % when it is exposed to 0.4 % nonionic surfactant-Triton X-100 and loses 10 % activity in the presence of 0.4 % Tween-80. Using fluorescence resonance energy transfer analysis, the protease showed the most specificity for the peptide Abz-KIRSSKQ-EDDnp with k _cat/K _m of 10,666 mM^?1?s^?1, followed by the peptide Abz-GLRSSKQ-EDDnp with a k _cat/K _m of 7,500 mM^?1?s^?1. Basic and acidic side chain-containing amino acids performed best at subsite S₁. Subsites S₂, S₃, S^′ ₂, and S^′ ₁, S^′ ₃ showed a preference for binding for amino acids with hydrophobic and basic amino acid side chain, respectively. High values of k _cat/K _m were observed for the subsites S₂, S₃, and S^′ _2. The sequence of the N-terminus (ANVVQSNVPSWGLARLSSKKTGTTDYTYD) showed high similarity to the fungi Penicillium citrinum and Penicillium chrysogenum, with 89 % of identity at the amino acid level.     

Kinetics and Mechanism of the Interaction of Di-μ-hydroxobis(1,10-phenanthroline)dipalladium(II) Perchlorate with Thioglycolic Acid and Glutathione in Aqueous Solution

The kinetics of interaction between di-μ-hydroxobis(1,10-phenanthroline)dipalladium(II) perchlorate and thioglycolic acid and with glutathione has been studied spectrophotometrically in aqueous medium as a function of the complex concentration as well as the ligand concentrations, pH, and temperature at constant ionic strength. The observed pseudo-first-order rate constants k _obs (s^?1) obeyed the equation k _obs = k ₁[Nu] (Nu = nucleophile). At pH = 6.5, the interaction with thioglycolic acid shows two distinct consecutive steps and both steps are dependent on the concentration of thioglycolic acid. The rate constants for the process are: k ₁ ≈ 10^?5 s^?1 and k ₂ ≈ 10^?3 dm³ · mol^?1 · s^?1. The association equilibrium constant (K _E) for the outer sphere complex formation has been evaluated together with the rate constants for the two subsequent steps. The other bio-active ligand, glutathione, showed a single step reaction depending on [ligand] with a second-order anation rate constant: the 10² (k ₂) values are (61.72, 79.20, 109.24 and 154.33) dm³ · mol^?1 · s^?1 at 20, 25, 30 and 35 °C, respectively. On the basis of the kinetic observations and evaluated activation parameters, plausible associative mechanisms are proposed for both interaction processes.     

Mechanism of the oxidation of hydrazoic acid by tetrachloroaurate(III) ion

The oxidation of hydrazoic acid in perchloric acid in the absence of added chloride under pseudo first-order conditions ([HN₃] » [AuCl ₄ ^? ]) is first order in [Au(III)]. Michaelis–Menten type of dependence (linear plots of k _obs ^?1 vs [HN₃]^?1) is observed with respect to [HN₃]. The k _obs is independent of ionic strength and the plot between k _obs ^?1 and [H⁺] is linear. The inner-sphere mechanism is consistent with the formation of an axial complex (K = 25 dm³ mol^?1) between AuCl₃(HO)^? ion and HN₃ prior to its rate determining decomposition (k = 0.0182 s^?1). It is inferred that the free radicals N ₃ ^? do not oxidise Au(II). The reaction becomes outer-sphere in the presence of added Cl^? ions which are inferred to form a cage around the hydronium ion surrounding the AuCl ₄ ^? ions. The penetration of N ₃ ^? through the cage is rate controlling and within the cage, the electron transfer from N ₃ ^? ion to AuCl ₄ ^? is fast. The value of the rate determining constant k ₂ is 0.547 dm³ mol^?1 s^?1 and the equilibrium constant K _Cl for the cage formation is 5 dm³ mol^?1 at 25 °C. It is calculated that the minimum HN₃ concentration required before the reaction exhibits zero-order dependence in HN₃ is 0.31 mol dm^?3 when [H⁺] = 0.18 mol dm^?3 at 25 °C.