Comments on “Quality assurance of nuclear analytical techniques based on Bayesian characteristic limits”

A paper by R. Michel in this journal (J. Radioanal. Nucl. Chem., 245 (2000) 137) describes, among other things, a numerical example: the calculation of characteristic limits in an analysis of ¹²⁹I via radiochemical NAA. A key problem in Bayesian characteristic limits is a proper formulation of the expression for the uncertainty associated with the measurand if its true value is equal to zero, ũ(0). We show that MICHEL’s expression for ũ ²(0) is not correct and propose a new one. Some numerical errors found in the paper are also indicated.     

Further studies in the advance prediction of gamma-ray spectra and detection limits in instrumental neutron activation analysis

This computational procedure, described earlier for NaI(Tl) gamma-ray spectrometry, has now been set up for Ge(Li) spectrometry measurements, has been extended further in various details, has been partially computerized, and has been tested experimentally on both biological and geochemical types of samples—with good results. The procedure enables one to compute, in advance of any activations, the approximate Ge(Li) pulse-height spectrum of a sample for any selected flux and irradiation, decay, and counting times —and to compute the lower limits of instrumental NAA detection of any trace elements of interest—if the principal composition of the matrix is known. Various other useful parameters are also readily calculated.     

Elemental analysis of a single-wall carbon nanotube candidate reference material

A material containing single-wall carbon nanotubes (SWCNTs) with other carbon species, catalyst residues, and trace element contaminants has been prepared by the National Institute of Standards and Technology for characterization and distribution as Standard Reference Material SRM 2483 Carbon Nanotube Soot. Neutron activation analysis (NAA) and inductively coupled plasma mass spectrometry (ICP–MS) were selected to characterize the elemental composition. Catalyst residues at percentage mass fraction level were determined with independent NAA procedures and a number of trace elements, including selected rare earth elements, were determined with NAA and ICP–MS procedures. The results of the investigated materials agreed well among the NAA and ICP–MS procedures and good agreement of measured values with certified values was found in selected SRMs included in the analyses. Based on this work mass fraction values for catalyst and trace elements were assigned to the candidate SRM.     

Opportunities for innovation in neutron activation analysis

Neutron activation laboratories worldwide are at a turning point at which new staff has to be found for the retiring pioneers from the 1960s–1970s. A scientific career in a well-understood technique, often characterized as ‘mature’ may only be attractive to young scientists if still challenges for further improvement and inspiring new applications can be offered. The strengths and weaknesses of neutron activation analysis (NAA) are revisited to identify opportunities for innovation. Position-sensitive detection of elements in large samples, Monte Carlo calculations replacing the use of standards, use of scintillator detectors and new deconvolution techniques for increasing the sensitivity are examples of challenging new roads in NAA. Material science provides challenges for the application of NAA in both bulk samples, ultrathin layers and ultrapure materials.     

Neutron activation analysis of semiconductor silicon

The determination of impurities in semiconductor silicon by nondestructive and destructive NAA is described. To improve the detection limit, a multiple beta—single gamma detector assembly is used. It is shown that²⁴Na is also produced from silicon by a (n, αp) reaction with reactor neutrons. The cross-section with fission neutrons is 1.8·10⁻⁹ barn.     

Evaluation of relative comparator and <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-NAA for characterization of Aboriginal Australian ochre

Ochre is a significant material in Aboriginal Australian cultural expression from ceremonial uses to its application on many types of artifacts. However, ochre is a complex material, with associated surrounding minerals potentially challenging the overall analysis. In recent literature several studies have attempted to characterize ochre by a variety of techniques to understand procurement and trade. However, ochre is difficult to differentiate on major elemental or mineralogical composition and requires a detailed analysis of its geochemical “fingerprint”. Neutron activation analysis (NAA) provides the high sensitivity (sub-ppm), precision and accuracy in multi-elemental analysis required for ochre. The elements of interest for ochre generally include rare earth elements (REEs) and certain transition metal elements as well as arsenic and antimony. Data from relative comparator NAA (MURR, University of Missouri, USA) is compared with data from k ₀-NAA OPAL (ANSTO, Lucas Heights, Australia). A discussion of the two methods will be examined for their utility in “fingerprinting” the provenance of ochre. The continuing importance of NAA to archaeometry will also be discussed.     

The Effect of Naphthalene-Acetic Acid on Biomass Productivity and Chlorophyll Content of Green Algae,Coccolithophore, Diatom,and Cyanobacterium Cultures

The application of biochemical stimulants to enhance biomass and metabolite productivity is being investigated here and may be a simpler approach to achieve our goals of higher productivity and lower costs than methods such as genetic modification. The research builds on prior work of screening various biochemical stimulants representing different types of plant growth regulators with the green alga, Chlorella sorokiniana. Here, we report the impact on biomass and chlorophyll productivity by comparing the delivery method of a previously identified superior stimulant, the synthetic auxin naphthalene-acetic acid (NAA), solubilized in ethanol or methanol. Algae evaluated included the green alga, C. sorokiniana, as well as a mixed consortium that includes C. sorokiniana along with two other wild-isolated green algae, Scenedesmus bijuga and Chlorella minutissima. It was found that NAA dissolved in ethanol was more effective in enhancing biomass productivity of C. sorokiniana. However, no differences were observed with the mixed consortia. The most effective treatment from this step, EtOH_500ppm + NAA_5ppm, along with two other NAA concentrations (EtOH_500ppm + NAA_2.5ppm and EtOH_500ppm + NAA_10ppm), was then applied to six diverse species of microalgae to determine if the treatment dosage was effective for other freshwater and marine green algae, cyanobacteria, coccolithophore, and diatoms. It was found that three of the species bioassayed, Pleurochrysis carterae, C. sorokiniana, and Haematococcus pluvialis exhibited a substantial boost in biomass productivity over the 10-day growth period. The use of ethanol and NAA at a combined dosage of EtOH_500ppm + NAA_5ppm was found to generate the highest biomass productivity for each of the species that responded positively to the treatments. If scalable, NAA and ethanol may have the potential to lower production costs by increasing biomass yields for commercial microalgae cultivation.     

Estimation of alert and change limits and its application in the plausibility control

In the clinical laboratory, one of the most objective ways to perform the final review of patients’ measured values is the use of computerized plausibility control (i.e., set of procedures used to decide whether a patient’s measured value is valid according to established clinical and biological criteria). This study is focused on the estimation of alert and change limits to be applied to detect doubtful patients’ measured values. These limits are useful to improve the final review of patients’ measured values since these limits are produced objectively and are selected according to the clinical laboratory needs, letting the clinical laboratory professional staff to save time and effort.     

Ultra-sensitive determination of K, Th, U and other trace impurities in liquid organic scintillators by NAA

We present a NAA method to determine ultratraces of K, Th, U and other trace impurities in liquid organic scintillators, which are known as ultrapure detector materials for neutrino or dark matter experiments. A combined optimization of relevant factors for sensitive NAA has been realized, leading to a sensitivity for U down to 10⁻¹⁶g/g. Samples of 250 ml have been irradiated up to 120 h at a thermal neutron flux of 5–8·10¹²·n·cm⁻²·s⁻¹. Acidic extraction, wet ashing and TBP-extraction are used for radiochemical separations. Finally, coincidence techniques are applied for increased sensitivity.     

Instrumental neutron activation analysis limits of detection in the presence of interferences

Many tables of neutron activation analysis (NAA) limits of detection, in the absence of interferences, for various irradiation and counting conditions, may be found in the literature. This paper presents a method for estimating, in advance, the instrumental NAA limits of detection for any elements of interest in any given matrix, including ones generating high interference levels. The rationale of the method is presented, and the procedure for applying it is illustrated.     

Microgels formed by electrostatic and hydrophobic interaction of naphthaleneacetic acid with β-cyclodextrin-grafted polyethyleneimine

Microgels were prepared by physically cross-linking β-cyclodextrin-grafted polyethyleneimine (βCD-PEI) using a hydrophobic acidic compound, naphthaleneacetic acid (NAA). Under a strong acidic condition (e.g., pH 3.0), fibrous microgels were observed on a scanning electron microscope (SEM) possibly due to the intermolecular electrostatic interaction of NAA with PEI. In the range of pH 4.0 to pH 8.0, globular microgels were found possibly because an intramolecular electrostatic interaction prevails over an intermolecular interaction. At pH 9.0 and pH 10.0, neither fibrous nor globular microgels were observed due to lack of the electrostatic interaction and the hydrophobic interaction of NAA with βCD-PEI. The release of fluorescein isothiocyanate-dextran (FITC-dextran; M.W., 10,000) from the microgels increased with increasing pH. At pHs higher than pH 3.0, not only the diffusion of the solute, but also the dissolution of the microgels could contribute to the release.     

Different methodologies in neutron activation to approach the full analysis of environmental and nutritional samples

Different methodologies of neutron activation analysis (NAA) are now available at the Technological and Nuclear Institute (Sacavém, Portugal), namely Compton suppression, epithermal activation, replicate and cyclic activation, and low energy photon measurement. Prompt gamma activation analysis (PGAA) will be implemented soon. Results by instrumental NAA and PGAA on environmental and nutritional samples are discussed herein, showing that PGAA — carried out at the Institute of Isotope Research (Budapest, Hungary) — brings about an effective input to assessing relevant elements. Sensitivity enhancement in NAA by Compton suppression is also illustrated. Through a judicious combination of methodologies, practically all elements of interest in pollution and nutrition terms can be determined.     

Metrological role of neutron activation analysis. IA. Inherent characteristics of relative INAA as a primary ratio method of measurement

In a series of three papers, the inherent characteristics of relative instrumental neutron activation analysis (INAA) as a primary ratio method of measurement, the unique functions of parametric INAA as an ideal back-up method of the relative INAA, and the valuable role of INAA in characterization of sampling behavior of individual elements in certified reference materials (CRMs) will be discussed. In this paper, the first of the series, the uncertainty evaluation and the traceability of values measured by neutron activation analysis (NAA), especially instrumental NAA (INAA), will be described to demonstrate the method at its ”the state-of-the-art” level can meet CCQM criteria for a primary ratio method. The scope and examples will be given. Received: 19 March 2001 Accepted: 2 October 2001     

Determination of silver in biological reference materials by neutron activation analysis

Silver in selected, predominantly biological, reference materials (NIST SRM 1515, 1547, 1549, 1566a, 1571, 1577b, 2704, CTA-OTL-1, and Bowen’s Kale) was determined using neutron activation analysis (NAA) in two different analytical modes: instrumental NAA with epithermal neutrons (ENAA), and NAA with radiochemical separation (RNAA). The ENAA mode was based on long-time 5-hour irradiation of samples in a special Cd lined box with counting after 8-month decay. The RNAA procedure consisted in 20-hour irradiation of samples, their decomposition/dissolution by alkaline-oxidative fusion, and precipitation of AgCl including several purification steps. Both methods provided Ag contents in the analyzed reference materials consistent with certified and/or literature values down to the ng·g⁻¹ level.     

Comparison of neutron activation analysis with other analytical techniques for the determination of inorganic constituents of milk powder

The contribution of different analytical techniques to the results of a recent IAEA intercomparison (A-11) of the determination of the inorganic constituents of a milk powder sample is discussed. In all, 43 laboratories from 24 countries reported results on 40 elements, “recommended” concentrations for 14 elements were established. NAA was the most important of the 9 techniques used in this run, it contributed 40% of all the results and all the results for 7 elements. Accuracy and precision of NAA proved to be good compared to those of other methods.     

Neutron activation analysis in the geosciences: Lost territory, or New Deal?

NAA was the first technique to facilitate extensive studies of trace elements in the geosphere. Since the first applications around 1950 a rapid development was observed during the following years due to improvements in radiochemistry, detectors, and electronics, which reached a maximum in the early 1970s with the studies of lunar rocks. Since then the use of NAA in the geosciences has gradually lost momentum, not only due to the fact that new analytical techniques have emerged but also because some of the knowledge acquired during the “golden years” may appear to have been forgotten. In the present paper some important milestones in geochemical analyses by NAA are reviewed, recent trends are discussed, and some priorities for future work are suggested. This revised version was published online in July 2006 with corrections to the Cover Date.     

Application of NAA to air particulate matter collected at thirteen sampling sites in eight Asian countries: A collaborative study

Air particulate matter (APM) samples (PM_2.5 and PM_10–2.5) were collected at 13 sampling points in 8 Asian countries and their chemical compositions were determined by using neutron activation analysis (NAA) with the k ₀-standardization method in addition to conventional comparative method of NAA. Analytical data showed that mass concentration and elemental composition of the APM collected are variable in terms of time and space, and are related to the characteristics of the sampling sites concerned. NAA was proved to be highly effective for the regional characterization of APM in chemical composition.     

A multiple time-gated system for pulsed digital gamma-ray spectroscopy

Neutron activation analysis (NAA) systems that use pulsed neutron generators (NGs) employ spectrum gating procedures to segregate nuclear processes by acquiring gamma-ray spectra separately when the generator is on (HIGH gate) and off (LOW gate). Often, the actual neutron burst lags the leading edge of the HIGH gate signal by a few μs. Thus, count rates vary not only between the on and off states of the NG, but within them as well. Recent advances in digital gamma-ray spectrometers that allowed the concurrent acquisition of data by sorting events into two separate spectra based on gate status suggested that a time-resolved analysis that further subdivided the neutron pulse cycle could obtain further information to separate gamma-rays produced by different nuclear reactions. In this paper we introduce a gating system for time-resolved NAA that is capable of concurrently acquiring as many as 16 spectra from up to 8 user-defined time intervals during each of the HIGH gate and LOW gate periods, each with all required timing and count rate information. We present the new gating system’s implementation, operation and some first experimental test results.     

Methodological developments and applications of neutron activation analysis

The paper reviews the author’s experience acquired and achievements made in methodological developments of neutron activation analysis (NAA) of mostly biological materials. These involve epithermal neutron activation analysis, radiochemical neutron activation analysis using both single-and multi-element separation procedures, use of various counting modes, and the development and use of self-verification principle. The role of NAA in the detection of analytical errors is discussed and examples of applications of the procedures developed are given.     

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.