Implementation of a methodology to analyse cylindrical 5-g sample by neutron activation technique,k 0 method,at CDTN/CNEN,Belo Horizonte,Brazil

Neutron activation analysis (NAA) is routinely applied to geometrical point-source or small samples because there are technical and theoretical difficulties to analyse larger samples weighing more than 0.5 g. The analysis of larger samples is very advantageous, because the analytical procedure will be less time consuming, it may be possible to reach lower detection limit for several elements, it decreases cost and overcomes the difficulties related to the representativeness of the sample when dealing with inhomogeneous volume or several small samples. Thus, increasing the amount of sample is a way to compensate for low flux of neutrons. This paper is about the establishment of a method at Laboratory for Neutron Activation Analysis, CDTN/CNEN, to determine the elemental concentrations in 5 g-samples, 25 times larger than usual samples analysed by neutron activation, k ₀ method, keeping the current irradiation and gamma spectrometry facilities. To develop this method, several aspects were evaluated such as detector efficiency over the volume source, neutron self-shielding during neutron irradiation, axial neutron flux gradient and gamma ray attenuation within the sample during counting. The results suggest that if an appropriate adjustment of the above mentioned parameters is done, the k ₀ method of NAA can provide satisfactory results also for larger samples than the samples typically used in NAA. The KayWin software proved to be a robust program analysing the larger samples weighing 5 g and cylindrical geometry as if it were a small cylindrical sample, producing reliable results. It was successfully implemented at Belo Horizonte, Brazil, fully following the basic principles of the k ₀ standardization method.     

Iron Quadrangle, Brazil: Elemental concentration determined by k0-instrumental neutron activation analysis

Summary The Iron Quadrangle, Minas Gerais, Brazil, is rich in mineral occurrences and is considered one of the richest mineral-bearing regions in the world. Most investigations in this region have dealt with the determination of arsenic and mercury but so far few studies have been carried out aiming at determining other important elements. Having in mind the potential risk caused by mineral activities, this study was developed in order to assess the potential influence of the soil on foodstuffs. The soil samples were collected from three sites inside and outside the Iron Quadrangle. The samples were analyzed at the Laboratory for Neutron Activation Analysis, CDTN/CNEN by the k₀-instrumental neutron activation analysis. This paper reports the elemental concentration determined in soil and emphasises the elements cited in the Brazilian environmental legislation for soil. This work also confirms the high elemental concentration of several minerals, however, it is difficult to distinguish the contamination from anthropogenic activities from the natural occurrence.     

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.     

k0-Instrumental Neutron Activation Analysis Establishment at CDTN, Brazil: A successful story

Since 1995 the k ₀ instrumental neutron activation analysis has been applied at Radiochemical Laboratory, CDTN/CNEN, Brazil, by means of TRIGA MARK I IPR-R1 research reactor. At that time , f, and T _n were determined and the most recent determination of these parameters confirmed the great stability of the reactor along these years. In order to verify the efficiency and accuracy of the method, several certified reference materials have been systematically analyzed. Participating in Intercomparison Exercises organized by IAEA has been an important, essential and useful procedure to quality control. CDTN is the only Brazilian Institute to apply the k ₀-INAA to determine elements by means of their isotopes through short, medium and long half life using its own nuclear reactor.     

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.     

Analysis of SMELS by k 0-based IM-NAA method using PFTS position of KAMINI reactor for quality control exercise

As a part of QA/QC of k ₀-based internal monostandard neutron activation analysis (IM-NAA), three types of synthetic multielement standards (SMELS) were analyzed using pneumatic fast transfer system irradiation position of KAMINI reactor, IGCAR. Radioactive assay of activation products was carried out by high resolution gamma ray spectrometry. IM-NAA was used to determine relative concentration ratios of 22 elements with respect to gold internal monostandard. Absolute concentrations were calculated using assigned concentration of Au in all the types of SMELS. Z-score values within ±1 at 95.5 % confidence level and percentage deviations within ±5 % indicated good quality of the results by IM-NAA in most of the cases. Using this methodology, an ilmenite mineral sample was analyzed and concentrations of 14 elements were determined using Sc as monostandard.     

Method validation procedures for environmental radiochemical measurements at AECS

The present paper describes the experience of the Atomic Energy Commission of Syria in relation to the application of Eurachem Guide on method validation for environmental radiochemical measurements. Methods validated include gamma and alpha spectrometry for natural and artificial radionuclides determination, and fluorometry determination for total uranium. Documents and records were first set to meet trackability and traceability requirements, where internal quality control mechanisms have been adopted. Methods stability was checked by means of Z-score control charts. Internal method validation parameters including method detection limits, repeatability limits, reproducibility limits, recovery coefficient and relative error were estimated. External method validation has been achieved by participating in international intercomparison exercises and proficiency tests organized by EML, IAEA and WU; some results of these activities are presented. Moreover, the application of both internal and external method validation gave the analysts in our laboratories more confidence in their skills, and it was of great assistance for our customers including regulatory authorities to evaluate the fitness of the method for their applications according to internationally agreed procedure. The steps followed here can be used for method validation in other laboratories with similar applications.     

Radiation stability tests of the SMELS materials in the LVR-15 experimental reactor at Řež

Radiation stability of a set of three synthetic multielement standards (SMELS) designed for validation of k ₀-standardization in neutron activation analysis was tested by monitoring mass and element content changes following irradiation at a high neutron fluence rate (up to 9^.10¹³ n^.cm^-2.s^-1) for stepwise increased periods of time. No mass changes were detected and for all the 26 elements investigated only a chlorine content loss was observed. Thus, radiation stability of the SMELS materials for the given purpose and their suitability for use also in high-power reactors was demonstrated.     

Critical evaluation of laboratory performance from IAEA-452 (fish scallop) inter-comparison exercise results

The International Atomic Energy Agency Marine Environmental Laboratory (IAEA-MEL) conducted an intercomparison exercise for the “Trace elements and methyl mercury in fish scallop: IAEA-452” in 2009. The Neutron Activation Analysis (NAA) laboratory at PINSTECH, Pakistan took part in this exercise. Comparison with the IAEA results showed that of the 18 elements reported to the IAEA 7 had unacceptable z-scores while the data for two elements was questionable (2< |z-score| <3). Upon investigation it was discovered that the large number of elements having unacceptable z-scores was due to human error and the greater difficulty in analyzing biological samples which have low amounts of trace elements. Therefore selection of values corresponding to matrix matched reference materials (RMs), such as IAEA-436 and IAEA-407, and to non-interfering peaks the results obtained became comparable to the IAEA results with only the result for As having |z-score|> 3.     

Using synthetic multi-element standards (SMELS) for calibration and quality control of the irradiation facilities in the BR1 reactor

The thermal to epithermal neutron flux ratio (f) and the deviation of the epithermal neutron spectrum from the 1/E shape (α) are essential parameters for the correct application of k ₀-standardized neutron activation analysis. Several methods are applied for the determination of f and α. They are based on Cd-covered multi-monitor or on bare-irradiations methods. The recently developed and characterized synthetic multi-element standards (SMELS) were designed as a validation tool for the proper implementation of the k ₀-NAA method in a laboratory. In particular, SMELS Type III contains Au and Zr, thus allowing the direct determination of f and α. It could, therefore, replace the traditional flux monitors. Furthermore, it could be used as a quality control material to monitor the stability of the irradiation facility and the detector. This paper presents the accuracy of the f and α determination and the feasibility of quality control using SMELS for irradiation channel Y4 of the BR1 reactor.     

Implementation of the <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-NAA method by using <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-IAEA software and the NAA#3 irradiation hole at the HANARO research reactor

This study intended to demonstrate the use of k ₀-IAEA software with the NAA#3 irradiation hole in the HANARO research reactor and the gamma-ray spectrometers at the NAA laboratory in the Korea Atomic Energy Research Institute (KAERI). NIST SRM 2586-Soil was chosen as a sample to validate the analytical protocol by using the k ₀-IAEA software. Twenty four elements were determined and the resultant deviations between the experimental results and the certified values were all within 10% except for Dy. In addition, an analysis of three types of synthetic multielement standards (SMELS) prepared by the Institute for Reference Materials and Measurements (IRMM) and Institute of Nuclear Science (INW) in Belgium was executed. The analytical results agreed well with the assigned values and the U-scores for most of the elements were lower than 2.     

Evaluation of Three Software Programs for Calculating True-Coincidence Summing Correction Factors

True-coincidence summing correction is an essential element in k ₀-based NAA¹ and becomes important when samples are counted with a high efficiency detector. This may be the case where large detectors are used or where samples are counted in or in the vicinity of the detector in order to achieve low detection limits in conjunction with low-flux reactors. In some laboratories coincidence correction is accomplished by calculating the coincidence correction factors. Since experimental validation of the calculations will reveal only the most significant errors and is a laborious task due to the high number of radionuclides involved, three laboratories decided to compare their calculated coincidence factors. Each laboratory uses a different software package. A comparative performance analysis was made of COINCALC developed at the INW of the University of Gent (implemented in SOLCOI by DSM Research), the software of the IRI, University of Delft, the Netherlands, and the software of the Ecole Polytechnique, Montreal, Canada. The overall approach, data and algorithms were chosen independently by each institute as the software was being developed and, so, the comparison has yielded a number of interesting conclusions. A follow-up investigation of the discrepancies found will probably allow the performance of each program to be improved.     

The preparation and homogeneity study of synthetic multi-element standards (SMELS) for QC/QA of k0-NAA

Three new synthetic multi-element standards (SMELS) were developed for testing the performance of the k ₀-standardization neutron activation analysis (k ₀-NAA) method when implemented in a laboratory. SMELS consist of a phenol-formaldehyde polymer matrix spiked with different groups of elements according to the half-lives of the formed radionuclides. They are classified as Type I for short-, Type II for medium- and Type III for long-lived radionuclides. This article presents the preparation of SMELS including different aspects such as choice of the matrix and spiking elements, chemical compounds, target concentrations, purity of the matrix and spiking procedure and the homogeneity study for all the spiked elements in order to demonstrate the quality of the produced materials.     

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.     

An inter-laboratory comparison study for the determination of copper and lead from the wastewater of printed circuit board manufacturing industry in Pakistan

This inter-laboratory comparison study was arranged for 28 laboratories from different public and private sector organizations in Pakistan having wastewater testing capabilities aimed at improving the quality and comparability of test results. This national inter-laboratory study was started in December 2003 and completed in July 2004. Laboratories were invited to analyze the wastewater collected from printed circuit board (PCB) industry for lead and copper contamination. The samples fulfill the criteria for homogeneity and stability as done by the reference laboratory. The results obtained from participating laboratories were analyzed in terms of Hampel Test for outliers, while the performance evaluation of the participating laboratories was done on the basis of Z-score. An assigned value derived from the participant's results was compared with a reference value provided by a reference laboratory. Overall >50% of the participating laboratories have shown good performance in this PT-program     

Trace element determination in a mussel reference material using short irradiation instrumental neutron activation analysis

The production of certified reference materials in Brazil, and the consequent availability to national end users, is an important task for the enhancement of Metrology in Chemistry status in the country, as these materials are used for method validation, equipment calibration and for establishing metrological traceability links. In this study, Instrumental Neutron Activation Analysis (INAA) was applied to the determination of bromine, chlorine, magnesium, manganese, potassium and vanadium in a mussel reference material produced at IPEN-CNEN/SP. For the determination of these elements via the comparative INAA method, the respective analytical radionuclides, ⁸⁰Br, ³⁸Cl, ²⁷Mg, ⁵⁶Mn, ⁴²K and ⁵²V, are short lived and then, short irradiations are used. Six subsamples from two bottles of the Perna perna mussel reference material were analyzed. Each subsample was simultaneously irradiated with elemental standards for 10 s at the IEA-R1 research nuclear reactor through a pneumatic transfer system. After suitable decay periods, gamma radioactivity measurements were carried out, using a hyperpure germanium detector. The accuracy of the method was checked by using the NIST SRM 1566b–“Oyster Tissue” certified reference material. The comparison of the results obtained in this study to the robust mean of the interlaboratorial collaborative trial used for the characterization of the mussel reference material was performed via z-score tests. The comparison showed that the short irradiation INAA method is suitable for the characterization of new reference materials.     

Theoretical investigations on analytical potential energy function and spectroscopic parameters for the state b3Πu of dimer 7Li2

The SAC‐CI (symmetry‐adapted‐cluster configuration‐interaction) method presented in Gaussian 03 program package is applied to investigate the adiabatic potential energy curves (PECs) of ⁷Li₂(b³Π_u). These calculations are performed at numbers of basis sets, such as 6‐311++G(3df,3pd), 6‐311++G(2df,2pd), 6‐311++G(df,pd), D95V++, D95(3df,3pd), D95(d,p), cc‐PVTZ, 6‐311++G and 6‐311++G(d,p). All the ab initio calculated points are fitted to the analytic Murrell‐Sorbie functions and then used to compute the spectroscopic parameters. The analytic potential energy function (APEF) for this b³Π_u state is reported. By comparison, the spectroscopic parameters reproduced by the APEF attained at 6‐311++G(2df,2pd) are found to be very close to the latest experimental findings. With the APEF obtained at the SAC‐CI/6‐311++G(2df,2pd) level of theory, a total of 62 vibrational states is found when J = 0. The complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants for these vibrational states are also reported. The reasonable dissociation limit for this state is deduced using the calculated results at present. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Validation of the determination of tin by <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-instrumental neutron activation analysis in foodstuff

Several recent intercomparisons and certification exercises have shown that the determination of tin in e.g. food samples and plastics is not straightforward. k ₀-Instrumental Neutron Activation Analysis (k ₀-INAA) offers some intrinsic quality control opportunities for the determination of the tin content in samples since several monitoring radioisotopes are formed. In this work we will discuss the validation of the determination of tin by k ₀-INAA using different reference materials. The results show that only few of these radioisotopes are reliable in terms of accuracy and that from a survey of the tin content in a range of canned foods detection limits as low as 2 mg/kg can be achieved.