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.     

Determination of k 0-factors and validation of k 0-INAA for short-lived nuclides

For standardization of k ₀-based instrumental neutron activation analysis, k ₀-factors for short-lived nuclides (half-lives—11 s to 37 min) of elements F, Se, Sc, Al, V, Ti, Cu, Ca, Mg, I, and Cl with respect to gold (¹⁹⁷Au) were determined using pneumatic carrier facility (PCF) at CIRUS reactor of BARC, Mumbai. Characterization of PCF was carried out by cadmium-ratio method using Au and Zr. The experimental k ₀-factors of the isotopes were found to be in good agreement with the recommended k ₀-factors in most of the cases, as evident from the values of % error and U-score at 95% confidence level. The method was validated by determining concentrations of elements through their short-lived nuclides in one type of the synthetic multielement standards (SMELS-I) obtained from SCK-CEN, Belgium. The method was also applied for determination of concentrations of some of the elements in two reference materials of IAEA, SL-3, and SL-1.     

In-beam determination of k0 factors for short-lived nuclides

The prompt -activation analysis (PGAA) facility at Budapest Research Reactor offers a unique possibility to perform in-beam measurements. Several k ₀ factors for decay -lines of short-lived nuclides have been determined accurately by means of in-beam activation. The present values compare well with literature data. New k ₀ factors are proposed for ^24mNa and ^60mCo.     

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.     

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.     

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.     

Quantu-design and development of a software package dedicated to k0-standardized NAA

This work shortly describes the main steps involved in the design and development of the software package Quantu, created to conduct k ₀-standardized NAA. The package comprises a database as well as two individual programs. Quantu-MCA is dedicated to (g-ray spectrum analysis and Quantu-INAA is the interface for the database administration, also dealing with k ₀-method calculations.     

The NAA method at Polytechnique Montreal: an efficient alternative way to use the k 0 NAA models

At Ecole Polytechnique Montreal, the philosophy in performing neutron activation analysis (NAA) is long-term and application oriented. Thinking long-term implies a good understanding of the fundamentals of the method, of the samples, of the tools, reactor and detectors, and there must be constant innovation that is experimentally validated with extensive measurements. Application oriented means a NAA method developed to provide users with fast, sensitive, accurate and reliable analyses for various types of materials. This philosophy dictates the manner in which the developments in the areas of NAA software, peak-area calculation, dead-time correction, detection efficiency model, k ₀ and Q ₀ values, neutron moderation and neutron self-shielding are carried out. This paper presents a survey of the Laboratory’s methodology, reviewing a few of its unique features such as detector efficiency calibration and sample related perturbations of the neutron activation. These features are used as examples to provide the reader with an understanding of the philosophy and the evolution of the NAA method at Ecole Polytechnique.     

Application of k 0-based NAA for multielement determination in serpentines and associated minerals

The k ₀-based neutron activation analysis method was applied for multielement determination in black and yellow serpentines along with two associated minerals namely altered and unaltered dolomites and intrusive rock dolerite, obtained from the asbestos mines of Cuddapah basin, Andhra Pradesh, India. Concentrations of 20 elements were determined and they were used to predict the process of formation of fibrous chrysotile asbestos. Majority of elements as well as REEs reveal the contribution of elements from both dolerite and dolomite during the process of contact metamorphism in forming the mineral serpentine.     

An electronic database with a compilation of k0 and related data for NAA

An electronic data base (DB) containing recently evaluated k ₀ and related data has been developed. The tables composing the DB are relationally linked to support data integrity. The purpose of the DB development is to make an official source of data used for electronic synchronization of the input parameters needed for the k ₀ methodology, which is developing in numerous laboratories. Such solution saves time when updating, ensures the quality of the primary data and hence of the analysis results, and due to the recording of the updating history preserves traceability of the data in time.     

The updated NAA nuclear data library derived from the Y2K k0-database

Values of 2200 m^.s^-1 cross sections, together with the associated nuclear data, are tabulated for 128 (n,g) reactions of interest in NAA. The values are derived from the Y2K database of experimentally measured k ₀-factors.     

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.     

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.     

Some aspects of quality assessment of the k0-based method of NAA

Neutron activation analysis is one of the analytical techniques often used for certification of reference materials. The k₀-based method of instrumental neutron activation analysis can also be applied in intercomparison runs in the certification process and therefore it is desirable to know its accuracy in advance. Possible systematic errors related to the application of nuclear data at given neutron flux rate parameters, that can affect the uncertainties of the results obtained by this specific method, are elucidated and error propagation factors calculated for a typical irradiation position in the TRIGA Mark II reactor of the Jozef Stefan Institute. It was found that these uncertainties are at the level of 1–2% on the average.     

The k0-standardization method and its multifacetness: an eminent tool to master NAA

Journal of Radioanalytical and Nuclear Chemistry - It is outlined in the present paper that the continuous development and multi-purpose implementation of the k0-standardization in NAA implies the...     

A simplified method to replace the Westcott formalism in k 0-NAA using non-1/v nuclides

The Westcott formalism was developed to accurately describe the activation of nuclides whose neutron capture cross-sections do not follow the 1/v-law and it was incorporated in the k ₀-method about 20 years ago. However, its implementation in the original fashion is not easy, requiring the use of a different formalism for the non-1/v nuclides, with a g(T _n) factor for the thermal neutron activation and an s ₀ factor for epithermal activation, the measurement of the neutron spectral index of the irradiation channel and the irradiation of a temperature monitor with each batch of samples as well. In this work we investigated the accuracy of maintaining the simpler formula of the Høgdahl convention for all nuclides and introducing the g(T _n) factor for the thermal neutron activation for non-1/v nuclides. The epithermal activation is calculated using a Q ₀-value estimated from the measured s ₀-value for non-1/v nuclides. This new approach has been shown, by calculations with the parameters of the neutron spectra of five irradiation channels, not to give a significant loss of accuracy relative to the Westcott formalism.     

Experimental determination of k 0, Q 0 factors,effective resonance energies and neutron cross-sections for 37 isotopes of interest in NAA

The recommended k ₀ nuclear data from 2003 has been re-investigated by some authors during the last decade, motivated by some discrepancies that were systematically observed during the analysis of reference materials. Their significant findings have not been included (yet) on a newer compilation, as it is difficult to draw conclusions on the accuracy of k ₀ and Q ₀ factors when the statistical population of independent experimental values are quite scarce. In some cases, a strong correlation to the adopted Q ₀ factor means that a direct comparison between the results of different authors is not possible if the data required for a proper renormalization was not provided. At the SCK-CEN and UGent (Belgium) we would like to continue with the experimental k ₀ determination exercises performed during the last years and to supply to the k ₀-community with the nuclear data of 37 additional target isotopes, for a total of 77 isotopes investigated since 2012. The isotopes were investigated on up to 4 channels of the BR1 reactor at the SCK-CEN, obtaining values with <2.6 % uncertainty. Our results are discussed and compared to the literature elsewhere.     

The impact of polyethylene vials on reactor channel characterization in k 0 -NAA

Reactor channel characterization is commonly performed by irradiating bare and cadmium-covered “fluence rate monitors”, avoiding as much as possible the use of irradiation vials and spacers to position the monitors inside the channel. However, in routine k ₀ -Neutron Activation Analysis often samples are packed in small polyethylene vials prior to irradiation. This work aims at studying the impact of typical NAA polyethylene vials (~1 mm wall thickness) on the determination of the f and α channel-specific parameters through the “Bare”, “Cadmium-Covered” and “Cadmium-Ratio” methods. The impact of these vials on each method was studied for 3 irradiation channels of the Belgian Reactor 1 at SCK·CEN (Mol, Belgium) with low to high f and α-values. The net impact was 1% on each parameter. Inconsistencies between the different methods were found when the impact of the polyethylene was neglected, implying that all determination methods must be pooled and thin monitors should be used for an accurate channel characterization.     

ROMOS: A new computer code for nuclide identification and concentration calculation in NAA using the k0-concept

The program ROMOS and the assisting program RECAL are presented. These programs were designed to facilitate nuclide identification and concentration calculation in NAA using the k₀-concept. For nuclide identification classical tests (energy match, decay factor) are complemented with a test of the saturation factor including the sensitivity of neutron acctivation analysis for the candidate nuclide. For nuclides emitting more than one gamma-energy the intensity of the observed peaks in the spectrum are compared. Thereby full account is taken of relative detection efficiency and true coincidence effects. Practical experience in using the interactive code shows that it is a convenient and time-saving working aid for an experienced experimenter.