Automation and Quality Assurance in the NAA Facilities in Delft

The facilities for instrumental neutron activation analysis in Delft are described. Technical details of the fast rabbit systems, the normal pneumatic rabbit system, the large sample facility and the various coaxial and well-type Ge-detector spectrometers and sample changers are given. The capacity of the facilities is in the order of 15,000 samples per annum for full multi-element analysis. The capacity of the fast rabbit systems for INAA for use with short half-life radionuclides is even larger. The facilities are accessible for use by scientists from other establishments and countries as well.     

Non-uniformity and representative sampling in NAA

An instrumental procedure of activation analysis has been developed to study the distribution of some minor components in synthetic granates, ferrites and glass charges in some environmental materials. The determination of the degree of non-uniformity by NAA has been used for the preparation of uniform mixtures and for representative sample estimation in the analysis of nonhomogeneous materials.     

The standardization of standardless NAA

This review describes how the original `standardless' (absolute and single-comparator) NAA-calibration methods, introduced in the mid-1960s, were stepwise upgraded with respect to their accuracy and manageability, leading to the launching of the k ₀-method in the mid 1970s. Next, an account is given of the achievements in the continuous development of the k ₀-standardization of NAA up to the present. Topics highlighted are:the k 0 -data library, the development of dedicated calibration procedures, extensions and limitations, computerization and quality control/assurance. Finally, a short outline is given of the international dissemination of the k ₀-methodology.     

The Feasibility of Combined NAA and Neutron Diffraction

By employing neutron (or X-ray) diffraction, the structure of crystalline materials can be determined. However, if an impurity in the crystal is present in concentrations below, say, 1·10^–4, its influence cannot be observed in the diffraction patterns. If the impurity present at low concentrations is to be localized, a signal uniquely attributable to the impurity must be obtained. In this paper, two such methods, based on the same principles as the "X-ray standing wave" technique, are proposed for neutrons.     

Application of NAA in diffusion studies

The diffusion of Mn₂+ ions in CoSO₄ , NiSO₄ and ZnSO₄ containing 1% agar gel as well as that of MnSO₄ in 1% agar gel was studied at 25 °C. The diffusion coefficientsat selected concentrations were determined by the zone diffusion techniqueand by measuring the concentration of diffusing ions using neutron activationanalysis.     

Automatic NAA: Saturation activities

A system for Automatic NAA is based on a list of specific saturation activities determined for one irradiation position at a given neutron flux and a single detector geometry. Originally compiled from measurements of standard reference materials, the list may be extended also by the calculation of saturation activities from k ₀ and Q ₀ factors, and f and a values of the irradiation position. A systematic improvement of the SRM approach is currently being performed by pseudo-cyclic activation analysis, to reduce counting errors. From these measurements, the list of saturation activities is recalculated in an automatic procedure.     

Uncertainty budget and validation of NAA using Reference Materials

Instrumental neutron activation analysis (INAA) has been used at the research reactor of the Institute of Nuclear Techniques for measuring different types of samples for many years. For standardization purposes, the single comparator method has been applied. Since the theoretical basis of NAA is well understood, the sources of uncertainty can be well estimated, detailed uncertainty calculations have been recently performed to meet the increasing demands for method validation. INAA was validated by the analyses of sets of reference materials (RM), selectivity was controlled, accuracy and precision of the method as well as linearity, detection limits and measuring ranges were determined. Under the conditions of QA/QC, NAA can meet the high demands of trace element analysis. This revised version was published online in August 2006 with corrections to the Cover Date.     

In vivo measurement of nitrogen by NAA

Nitrogen in the human body is measured in vivo using prompt neutron capture gamma-rays. The quantity of nitrogen can then be used as measured of protein. Data are presented on three groups of subjects; volunteers of different ages, those with liver ailments, and those on peritoneal dialysis. The data show that the nitrogen measurements given information (in accord with clinical findings) which is not given by indirect methods of estimating lean body mass.     

Comparative PGAA and NAA results of geological samples and standards

Concentrations of major and trace elements in volcanic rock and soil samples, including geological standard reference materials, were determined by neutron activation analysis (NAA) and prompt gamma activation analysis (PGAA), both using the k ₀-standardization method. The paper highlights the different experimental procedures, such as sample preparation, data collection and spectrum evaluation. In geological samples, PGAA gives precise results for major elements (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K and—as a unique method—for H), for some of the light trace elements as B and Cl, as well as for Sc, S, Cr, Co, Ni, Cd, Nd, Sm and Gd. NAA is sensitive for the rare earth elements, and for many major (Ti, Al, Fe, Mn, Mg, Ca, Na, K) and trace elements (e.g.: Sc, V, Cr, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Zr, As, Sb, Ce, Ba, Hf, Ta, W). For most major elements the results obtained by the two methods show good agreement. The comparison of the results obtained for trace elements is not always possible, since PGAA is less sensitive and concentrations are often below its detection limits. Nevertheless, the complementarity of NAA and PGAA allows nearly panoramic analysis of geological materials.     

A program for evaluation of NAA spectra

A program for qualitative and quantitative analysis of spectra obtained by comparative NAA method is described. It includes peak search, calculation of essential peak parameters, isotope identification and estimation of concentrations and/or detection limits of nuclides, corrected for cooling time and decay during measurement. Corrections for blank samples and peak interference are performed as well. Uncertainties estimation of final results are performed according to the error propagation law. The program is aimed to help an experienced user to calculate the results of analysis but the possibility for automatic mode for routine analysis is provided as well.Supported by International Atomic Energy Agency through the research contract 7268/RB.     

Accuracy and uncertainty in radioactivity measurement for NAA

The basic assumptions of activation analysis are that the induced radioactivity is proportional to the amount of analyte, and that the quantity of radioactivity can be related simply to the number of counts observed. Quantitative measurement of activity (and of its uncertainty) is not always simple, especially when accuracy better than a few percent is sought. Recent work with ⁷⁷Ge and ⁷⁶As has demonstrated that the accuracy of half-lives in the literature is sometimes insufficient. Despite these and other problems, quantitative understanding and documentation of uncertainties can be accomplished, providing demonstrable quality assurance and supporting claims of traceability to the Système International.     

k0 and Comparator NAA: Influences and Interactions

A discussion is held on mutual influences and interactions between k ₀- and (relative) comparator-type NAA. Examples are given concerning: (1) the application of comparator-type NAA in the quality control/quality assurance of the IRMM-530 Al-0.1%Au neutron flux monitor developed for use in k ₀-NAA, (2) the utilization of the k ₀-method of calibration as a tool for the quality assurance of comparator-type NAA, (3) the introduction of corrections for detection efficiency and true-coincidence (of primordial importance in k ₀-NAA) in comparator-type NAA, (4) the development of k ₀-type standardization for use in prompt gamma neutron activation analysis, and (5) the renewal of insights in the traceability of k ₀- and comparator-type NAA.     

Sedimentation process in Ariake Bay using NAA and gamma-spectrometry

In order to assess the effect of marine and terrestrial environmental change in the last decades on the sedimentation environment in Ariake Bay, we collected three sediment cores. The concentrations of natural and anthropogenic radionuclides, major elements, and rare-earth elements were measured using gamma-spectrometry and neutron activation analysis. Vertical distributions of both radionuclides and sedimentation rates, determined using Cs-137 and Pb-210_ex dating methods, varied significantly among the sites.     

The role of NAA in nuclear chemistry education

One of the missions of our Institute is the promotion of basic nuclear teaching for students as well as professional teaching for workers in nuclear industry and research. For nuclear chemistry education, we present here a one day teaching course on radioactive decay and nuclear reactions, and a two or three days course based on reactor irradiation of uranium oxide, instrumental and radiochemical analysis of fission products. In the first experiment, the neutron capture is presented as an example of nuclear reaction; the neutron activation of a silver coin with a Am-Be neutron source, followed by γ-ray spectrometry, is used to identify three radionuclides of silver and to calculate their half-lives. In the second experiment, our teaching reactor is used as a neutron source with a flux about 10¹⁰ n·cm⁻²·s⁻¹ at a low thermal power (10 kW). This low flux allows us to irradiate a small uranium sample which is usable for spectrometry after a short cooling time of about two hours. The first day is reserved for instrumental analysis of the fission products and a second day for the radiochemical separation of a fission radionuclides. With these experimental results, the students have to calculate the number of fissions in the irradiated sample. On optional third day for postgraduate students is devoted to the presentation of NAA and some applications as uranium determination by the fission product spectrometry.     

Standardization of NAA Using the Activation Equation and Isotope-Related Constants

A standardization method for NAA has been developed based on the activation equation and on isotope-related k _i -values that are composite nuclear constants. This approach combines the simplicity of the absolute methods with nearly the same accuracy as that obtained by the relative ones. The k _i -constants are calculated from the well measured k ₀-factors and the neutron flux is determined as with the k ₀-method. A computer program was developed for the determination of the neutron flux parameters and the concentration of the trace element. These calculations start with the measured activity of the radionuclides.     

Analysis of natural milk and milk poweder samples by NAA

As a part of the Iraqi Food Analysis Programme /I.F.A.P./ the concentration of Na, Mg, P, Cl, K, Ca, Zn, Se, Br, Rb and I in natural milk collected from different regions of Iraq, and in milk powder samples have been determined by using the NAA technique. It was found that except for the elements I, Rb and Br the concentration of the elements was approximately identical in both the natural milks and milk powders.     

Study of organohalogen contaminants in yogurt by NAA and GC-ECD

The concentrations and distributions of total halogen (TX), extractable organohalogen (EOX) and extractable persistent organohalogen (EPOX) were determined in 20 kinds of yogurt specimens collected from Chinese supermarkets using neutron activation analysis (NAA) and gas chromatography equipped with a ⁶³Ni electron capture detector (GC-ECD). The results indicated that the halogens in yogurt mainly existed as non-extractable organohalogen compounds. About 25–30% of EOX was EPOX. EOCl and EPOCl were the main organohalogen species in yogurt. The average concentration of the identified organochlorine, such as organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs), was below 4% of EPOCl.     

Selenium determination in biological materials by NAA

Results for Se in several biological standard reference materials obtained by INAA and selective RNAA procedures developed in our laboratory, are presented and discussed. The comparison of selenium levels in selected blood plasma samples determined by non-destructive NAA and HG-AAS is also presented. The reproducibility and accuracy of the analytical procedure was tested and the results of these investigations were compared with the certified values.     

An automatic NAA analyzer for short-lived nuclides

An automatic activation analyzer with sample changer, pneumatic transfer system and fast pulse counting with real time pulse pile-up and dead time compensation is described. Transfer times between 80 and 300 ms from irradiation position to measurement station can be obtained. Counting losses are corrected within 10% up to total count rates of 120 kc/s.     

Local area networks in NAA: Advantages and pitfalls

Both at IRI and at NIST, Local Area Networks (LANs) are being used to acquire and process data from multiple gamma-ray spectrometers. In this paper, differences and similarities between three systems are discussed, resulting in recommendations for new systems to be set up.