Instrumental neutron activation analysis of sediment reference materials using the k0-standardization method

An instrumental neutron activation analysis technique has been developed for the determination of As, Au, Ba, Co, Cr, Fe, Hf, Sb, Ta, Th, U, W and Zn in large (10–15 g) geological samples using in-pool irradiation with a SLOWPOKE-2 reactor. The technique allows for the simultaneous irradiation of multiple samples using a neutron flux of between 4·10¹³ and 8·10¹³ n·m^–2·s^–1. The detection limits obtained using the analytical methodology described in this paper are acceptable for exploration geochemistry and the technique has been used to analyze samples collected as part of a metallic minerals survey of Jamaica.     

Instrumental neutron activation analysis of Moroccan geological samples using the k0-standardization method

Instrumental neutron activation analysis (INAA) for traces and major elements of several geological samples from “Zgounder” region in Morocco was performed utilizing the k ₀-standardization method. Sample irradiation has been done by the 250 kW Triga Mark II reactor at Jozef Stefan Institute in Slovenia. Due to its accuracy, sensitivity and specificity, the k ₀-standardization method is the most suitable method for non-destructive multielement analysis mainly for trace elements in rocks. It requires an accurate knowledge of the parameters of the irradiation facilities and other instrumentation parameters. It is an absolute standardization method, where the absolute nuclear data are replaced by a nuclear constant, the k ₀-factor, determined experimentally with high accuracy. More than 40 elements were determined using about 30-second short and about 7-hour long irradiations. Gamma-rays emitted from the irradiated samples have been determined by a high purity germanium detector. Accuracy was assessed using the standard reference material AGV-1. This was less than 1% for major elements and about 5% for traces. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of trace elements in reference materials by the k(0)-standardization method (INAA)

Instrumental neutron activation analysis was applied to four reference materials: NBS 1573 (Tomato Leaves), NBS 1645 (Citrus Leaves), NBS 1645 (River Sediment), and IAEA MA-A-2 (TM) (Fish Flesh). The k(0)-standardization method was used. The results are compared with (i) reference values (mostly non-certified) and (ii) published values obtained by other methods. Good agreement is found for most of the elements. For some elements, large discrepancies are observed.     

Accuracy and applicability of the k0-standardization method

The present paper deals with the accuracy and applicability of the k₀-standardization technique in NAA. Topics included are: user-oriented outline of the method, relevant nuclear data (k₀, Q₀, tc.), the non-1/E epithermal flux distribution, small detector separations and/or extended source geometries, (n, ) reactions with a Westcott-g1, primary interferences, subsequent (interrupted) irradiations, the non-constancy of the neutron flux during irradiation, and a final account of the accuracy. Although the paper is written in terms of the k₀-methodology, a good deal of the considerations can be transferred to most types of single-comparator standardization.     

Instrumental neutron activation analysis based on k0-standardization method as compared with other methods in the analysis of the IAEA inter-comparison test

Results of inter-comparison test organized by the IAEA are analyzed according to the contribution and performance of INAA as non-destructive method for trace elements analysis as compared to other techniques. Several methods were employed for certifying the biological sample (IAEA-0140) and were also compared. It is shown that NAA is the method of a good accuracy and precision. The biological sample has been investigated by INAA based on semi-absolute technique. More than 30 elements have determined without using standards. The reference materials, which are certified in this manner and utilized as primary standard, are also discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Computer-assisted reactor NAA of geological and other reference materials,using the k0-standardization method: Evaluation of the accuracy

A scheme for instrumental neutron activation analysis of ancient and medieval glasses is proposed. The combination of three irradiations (short time, pile and epithermal) enables the determination of 34 elements. The accuracy of the method is evaluated by analyzing two glass standard reference materials. Results from the analysis of three glasses from different times are presented.     

Determination of trace halogens in rock samples by radiochemical neutron activation analysis coupled with the k0-standardization method

Radiochemical neutron activation analysis coupled with the k₀-standardization method (k₀-RNAA method) was applied to silicate rock samples for the simultaneous determination of trace halogens (Cl, Br and I). Analytical results obtained by the k₀-RNAA method for geological standard rocks and meteorite samples agreed with those determined by the conventional comparison method conducted in the same set of experiments, suggesting that the k₀-RNAA method is as reliable as the conventional method. Our data for these samples are in good agreement with their literature values except for rare cases. Detection limits calculated under the present experimental condition are sufficiently low for Cl and Br but not for I for typical geologic and meteoritic samples. The k₀-RNAA method coupled with longer neutron-irradiation is expected to yield satisfactorily low detection limits for halogens including I in these samples.     

Recent advances in the k0-standardization of neutron activation analysis: Extensions,applications, prospects

This paper reports on the contribution made by some cooperating laboratories to the further development of the k₀-method. As to the extensions and improvements, emphasis is put on the availability of an Al–0.1% Au reference material for the k₀-standardization of NAA, on the counting of large-diameter samples, on the use of a low-energy photon detector, and on the introduction of the Westcott formalism for the handling of non-1/v (n, ) reactions. A survey is given of a large variety of scientific and industrial applications, including the analysis of biological, geological and geochronological samples, various kinds of reference materials, high-purity products and ceramics, and a number of environmental pollution indicators. As shown, the advantage of the k₀-standardization will be fully exploited with an increasing level of automation in NAA laboratories. Eventually, new measurements and evaluations of k₀-factors and related nuclear data are given in an Appendix.On leave from: Central Research Institute for Physics (KFKI), H-1525 Budapest 114, POB 49, Hungary.     

Comparison of relative INAA and k 0-INAA using soil and sediment reference materials

The objective of this work was to compare the results obtained by the relative INAA and k ₀-INAA methods for the same input parameters (sample mass, nuclear data, net peak area for the same gamma line and the same measurement and same cooling and measurement times). In total eight environmental soil and sediment reference materials (RM) or certified reference materials (CRM) from different producers were analysed. In this work only the recommended or certified values were considered, allowing comparison of the two methods for 30 elements. The results point out that k ₀-INAA possesses superior qualities compared to relative INAA, being insensitive to flux gradients, and independent of recommended/certified values in RMs/CRMs, often used as standards in relative INAA.     

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.     

Status and recent developments in the k0-standardization method

After critical evaluation of a number of existing standardization methods a new approach introducing generalized k₀-factors was suggested in 1975 for use in (n, γ) reactor neutron activation analysis (RNAA). In order that the new method could soon be applied competitively in actual analytical work a cooperation between the Activation Analytical Laboratories of the Central Research Institute for Physics (KFKI), Budapest and the Institute for Nuclear Sciences (INW), Gent was established to determine the k₀ and other related nuclear data (Q₀, T_1/2, Ē_r, etc.) with a high accuracy, to develop procedures for monitoring essential irradiation and measuring parameters (Φ_s/Φ_e, α, ∈_p, , etc.) as well as to share experiences when applying the method. This paper summarizes the main results of this cooperative work obtained in the last five years. The current status and recent developments in the k₀-method are reviewed and a “Status and Request List” compiled from more than a thousand surveyed nuclear data on about 150 analitically important (n, γ) reactions in being prepared to suggest new or refined measurements and to prevent the use of unreliable data.     

Neutron activation analysis of semiconductor materials

Two examples of the use of neutron activation analysis for the characterization of semiconductor materials are given. 23 elements were determined in ASTM silicon intercomparison samples. Most elements are below the detection limits, which vary between 0.009–300 ng/g. CdS/CdTe thin films have been characterized by determining the Cd, Te, Cl, I and In concentrations of dissolved films. Parallel determinations in different samples of films prepared under identical conditions agreed within 0–53% (average deviation 21%) for Cl, Cd, In and I in CdS and 1.6–22% (average 8.7%) for Cd and Te in CdS/CdTe, respectively. It was determined both by NAA and resonance ionization spectrometry (RIS). The order of magnitude of the results was 1 ng/g and they agree within the range 7–64% (average difference 25%). The analytical procedures are described and discussed.     

Neutron activation analysis of biological materials by the monostandard method

Instrumental neutron activation analysis by the monostandard method has been applied to the analyses of biological NBS standard reference materials; 1571 Orchard Leaves and 1577 Bovine Liver. Aluminum foils containing 0.100% gold or 2.00% cobalt were used as the monostandards. The gamma-ray spectral data were recorded on punched paper tape and were analyzed by a computer assisted data processing. The following 25 elements were determined: Al, Ca, Cl Cu, Mg, Mn, V (by short period irradiation), As, Ba, Br, Co, Cr, Cs, Eu, Fe, Hg, K, La, Na, Rb, Sb, Sc, Se, Sm and Zn (by long period irradiation). The results were compared with the certified values by NBS and the reported values in literatures to prove the reliability and accuracy of the monostandard method.     

Multielement determination of typical diet reference materials by neutron-induced prompt gamma-ray analysis using k 0 standardization

Multielement determination in reference materials of diet and its relatedsamples has been studied by a k 0 based neutron-induced prompt gamma-ray analysis(PGA) by using cold and thermal guided neutron beams of JRR-3M at JAERI. Hydrogen,B, C, N, Na, S, Cl, K and Ca were determined in the reference materials ofNIES and NIST typical diet and milk powder samples. Analytical results ofthe NIST Standard Reference Materials agreed with the certified values towithin 7%.     

Neutron spectrum correction of k0-factors for k0-based neutron-induced prompt gamma-ray analysis

Neutron spectrum correction has been attempted for the k₀-factors of the non-1/v elements which are affected neutron spectrum difference. Effective g-factors and Westcott g-factors, which are neutron spectrum correction factors obtained from an actual neutron spectrum and the Maxwellian distribution, respectively, for the non-1/v elements were calculated using their neutron cross section data of JENDEL-3.2. The neutron spectrum correction was made for the measured k₀-factors of the non-1/v elements such as Cd, Sm and Gd with the cold and thermal guided neutron beams of JRR-3M using the g-factors. The corrected k₀-factors between the cold and thermal neutron beams using both g-factors for both neutron beams agreed well for Cd. However, 9 to 44% deviations have been found for Sm and Gd, respectively.     

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.     

Development and implementation of the k0-standardization and other parametric methods of INAA in Cuba. Part I

This paper explains chronologically the implementation of thek ₀-standardization and other parametric methods in Cuba. Fundamental and applied results in the determination of the most important parameters are obtained, using the IBR-2 at Dubna and Triga Mark III at Mexico reactor facilities. Some modifications in the Stoughton-Halpering convention, and its comparison with the modified Westcott and Høgdahl method are presented. The application of the described methods at the CS-ISCTN low flux facility, using the big samples techniques, is presented.     

k0-NAA quality assessment by analysis of different certified reference materials using the KAYZERO/SOLCOI software

A suite of natural matrix reference materials (RMs) were used to assess the quality of analytical results obtained by k ₀-instrumental neutron activation analysis (k ₀-INAA) at the Joef Stefan Institute (IJS). Five certified reference materials (CRMs) from the Institute for Reference Materials and Measurements (IRMM), two standard reference materials (SRMs) from the National Institute of Standards and Technology (NIST), three RMs from the International Atomic Energy Agency (IAEA) and one RM from IJS were analyzed. Altogether, results for twenty-four elements in inorganic matrices and twenty-nine elements in organic matrices, obtained by k ₀-INAA, were compared to certified values. Results obtained show good agreement with certified or assigned values except for Fe, La, Nd, Sm and U in inorganic matrices, and Ag, Al and Cr in organic matrices.     

Correction for neutron induced reaction interferences in the NAA k0-standardization method

A study is made of the correction, in k₀-standardized NAA, for interferences caused by fast neutron induced threshold reactions, second order reactions and²³⁵U-fission. The following examples are elaborated: determination of the Cr and Sc concentrations in a reference human serum, corrected for the⁵⁴Fe(n,)⁵¹Cr and⁴⁴Ca(n,;^–; n,)⁴⁶Sc interferences, respectively, and the determination of Zr, Cs, La, Ce, Nd and Sm concentrations in USGS BCR-1 and G-2, corrected for²³⁵U(n, f) interference. A detailed uncertainty analysis and a comparison of the analytical results thus obtained with other literature values proves that the interferences can be accurately corrected for by employing the usual neutron flux monitors in the k₀-method, namely a Zr-foil and a dilute Au–Al alloyed wire.