Application of neutron activation analysis to the measurement of isotope abundance shifts in calcium and potassium

A simple method for the measurement by neutron activation analysis of the isotopic abundance shifts of⁴⁴Ca and⁴¹K in compounds of low volatility is described. Extraction and measurement procedures for the radioactive argon isotopes (³⁷Ar,³⁹Ar and⁴¹Ar produced by (n, α) and (n, p) reactions are also given. The results obtained demonstrate that the accuracy for the measurement of δ⁴⁴Ca is better than by the mass spectrometric method; in the case of δ⁴¹K measurement the accuracy is the same as that obtained with the mass spectrometer. Interfering reactions which yield other rare gases, and their relative contribution to the error in the measurement of δ values are also discussed.     

Volumetric method for the determination of uranium in the active process solutions

The DAVIES and GRAY method for the determination of uranium has been scaled down to facilitate the analysis of the radioactive solutions encountered in the fuel reprocessing plants. The sensitivity of the end point detection is improved by carrying out suitable modification in the procedure. Two procedures are described: (1) 70-ml procedure for the determination of 5–25 mg uranium, and (2) 30-ml procedure for 1–5 mg of uranium. The coefficient of variation is about 0.2% for 2–25 mg of uranium.     

Neutron activation analysis by combined capture and decay gamma-spectrum method

The usual method of the neutron activation analysis is performed by the measurement of the characteristic nuclear radiations of the produced radioactive isotope by neutron irradiation. An advance in this field has recently been proposed in which the prompt capture γ-rays are observed in addition to the nuclear radiation of the produced nucleus. The characteristic energy spectra of these two kinds of γ-radiations are the main basis for the combined activation analysis method. The experimental setup consists of a γ-radiation pulse height energy spectrum system which is synchronized with a pulsing neutron generator of ‘D—T’ or ‘D—D’ reaction. The present results indicate that a qualitative and semi-quantitative determination of a number of elements is feasible, with an overall error of 10–15%.     

The use of the microtron for the activation analysis of pure metals and alloys

Oxygen and carbon concentrations up to 0.06 ppm and 0.03 ppm respectively were determined in high purity metals such as Fe, Cu, Nb, Mo, In and some others. Analytical procedures and results of the determination of alloying additives in a number of rare metal alloys are given. The relative standard deviation constitutes 0.02 to 0.04. Accuracy of the procedures used is confirmed by a comparison of experimental results with those of the other analytical methods. Experimental data on the sensitivity of determining 35 elements are reported on irradiating them with thermal neutrons and a bremsstahlung emitted by the microtron. For most elements (for radioactive isotopes having a half-life of above 2 min.) sensitivity of the analysis is 10⁻⁶ to 10⁻⁸, g, at the microtron current of 30 μA and irradiation time of less than 10 min.     

Activation Analysis—Its Present State of Development and Its Importance as an Analytical Tool

Activation analysis is one of the most important methods available for the determination of traces of elements and of isotopes. One special advantage of activation analysis is its ability to cope with the simultaneous determination of many elements with very high detection sensitivity–for many elements lying below the ppb level. In some cases as little as 10^?14—10^?15g of an element can be detected. A number of sources of systematic errors common to other analytical procedures, mainly those caused by the blank, are eliminated in activation methods. The disadvantages may be seen as the inconvenience of handling radioactive materials, the dependence on large irradiation facilities, and sometimes the unavoidably long irradiation and cooling periods. On account of its unique capabilities activation analysis finds applications in all fields of endeavor where minute amounts of elements are of significance, from materials research through medicine to archaeology. Further improvements in performance and increases in scope are seen to lie in the development of new radiation sources, activation techniques, measurement systems, and separation procedures.     

Application of80m Br to the semi-automated analysis of bromine in biological fluids

A method is presented for the determination of bromine in biological fluids that demonstrates the possibility of adapting neutron activation analysis to large-scale, routine programs. By means of a simple and inexpensive semi-automated system radioactive bromine is separated from one hundred samples per day. A new procedure for determining bromine through measurement of the 36-keV γ-ray of^80m Br has been developed and incorporated into this method. The advantages achieved with this multipurpose separation system and low-energy γ-spectrometry are demonstrated through analyses of urine, serum, plasma and saliva.     

Should the Poisson statistical density function be used in the mesurement of short-lived isotopes?

The conditions under which the Poisson statistical density function adequately describes the counting of a radioactive isotope are examined and found that for counting processes where λt≳1, where λ is the decay constant and t the counting period, one of the fundamental properties, namely the condition of stationarity, is violated rendering application of Poisson statistics invalid. The Ruark-Devol statistical density function, a binomial, is instead shown to be satisfactory since it is capable of describing radioactive disintegration where the only fundamental property is independence and its use is recommended in both activation analysis and medical imaging when the half-life of the isotope of interest is short compared to the period of observation. It is pointed out that no satisfactory expression incorporating the distortion produced by dead-time on the statistical density function has yet been derived but the practical implications of the adoption of the Ruark-Devol function are discussed with respect to standard deviation and precision of the measurement. It is shown how the application of the Poisson statistical density function, under conditions of tλ≳1, is not only invalid but also overestimates the standard deviation significantly.     

The determination of tellurium in geological materials using radiochemical neutron activation analysis with a low energy photon detector

A method is described for the trace level determination of Te in geological materials with a detection limit of 5–10 ppb. Destructive thermal neutron activation analysis is used with relatively simple radiochemistry employing efficient precipitation and ion exchange techniques. A germanium Low Energy Photon Detector (LEPD) is used for radioassaying which allows the relatively aboundant X-rays from^123mTe to be measured. This radioactive isotope emits Te Kα and Kβ X-rays at 27–31 keV which are readily resolved by the LEPD and therefore allows interference effects from fission product Te to be minimised giving reliable trace level data of high accuracy. The validity of the method is demonstrated by reporting analytical data for Te in a range of USGS Standard Rocks.     

Instrumental neutron activation analysis of geological and pedological samples. Further investigation of epithermal neutron activation analysis using monostandard method

A comparative study is presented on neutron activation analysis of rock and soil samples using whole reactor neutron spectrum and epithermal neutrons with both relative and monostandard procedures. The latter procedure used with epithermal neutron activation analysis of soil samples necessitated the use of the “effective resonance integrals” which were determined experimentally. The incorporation of the β factor, representing deviation of reactor epithermal neutron flux from 1/E law, is developed in the present work. The main criteria for the choice of one or more of the procedures studied for a given purpose are also indicated. Analysis of 15 trace elements, Ca and Fe in the standard Japanese granite JC-1 using monostandard epithermal neutron activation gave results in good agreement with the average literature values. This paper is dedicated to the 80th birthday of Professor Dr. Robert Klement, University of Munich.     

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.     

Improved method for the separation of radioactive strontium from various samples by mixed solvent anion exchange

Procedures for the separation and determination of⁹⁰Sr in liquid samples, with cation and anion exchangers have been described. Strontium, yttrium and other cations bind to the cation exchanger and are eluted from the column by means of nitric acid. Separation of yttrium and strontium from other cations is carried out on columns filled with strong base anion exchangers in nitrate form with alcoholic solutions of nitric acid. This separation method enables the determination of⁹⁰Sr through yttrium on a low-level gas flow α, β-counter, as well as through strontium on a lowlevel liquid scintillation counter by means of Cherenkov counting. Such procedures have been tested by the determination of⁹⁰Sr in water, wine, medium radioactive liquid waste samples, milk and clover samples. For comparison, the determination has also been carried out by the standard method. It has been showed that the developed procedures might produce a high efficiency in strontium separation and a satisfactory accuracy of determination.     

Neutron activation analysis of impurities in gallium phosphide

Gallium phosphide is a new type of semi-conductor material. Although this substance becomes highly radioactive after neutron irradiation, because of the nature of its component elements (gallium and phosphorus) the chances were that the great sensitivity of the neutron activation technique would at least partly solve this very difficult trace analysis problem. The possibilities of non-destructive analysis of long lived elements (Co−Sb−Sc−Zn−Fe...) were investigated first. To extend this method to the determination of medium-life elements, different methods of radiochemical separation plan was worked out. Finally the method developed gives quantitative analysis of fourteen elements (Ag−As−Au−Ba−Co−Cr−Cu−Fe−Ir−Na−Rb−Sb−Sc−Zn) amounting very often less than one ppb.     

FluMag-SELEX as an advantageous method for DNA aptamer selection

Aptamers are ssDNA or RNA oligonucleotides with very high affinity for their target. They bind to the target with high selectivity and specificity because of their specific three-dimensional shape. They are developed by the so-called Systematic Evolution of Ligands by Exponential Enrichment (SELEX) process. We have modified this method in two steps—use of fluorescent labels for DNA quantification and use of magnetic beads for target immobilization. Thus, radioactive labelling is avoided. Immobilization on magnetic beads enables easy handling, use of very small amounts of target for the aptamer selection, rapid and efficient separation of bound and unbound molecules, and stringent washing steps. We have called this modified SELEX technology FluMag-SELEX. With FluMag-SELEX we have provided a methodological background for our objective of being able to select DNA aptamers for targets with very different properties and size. These aptamers will be applied as new biosensor receptors. In this work selection of streptavidin-specific aptamers by FluMag-SELEX is described. The streptavidin-specific aptamers will be used to check the surface occupancy of streptavidin-coated magnetic beads with biotinylated molecules after immobilization procedures.     

Sub-micron wear measurement using activities under the free handling limit

In the present work we demonstrate the development of a thin layer activation (TLA) method to be able to measure micrometer wear or less by using radioactive tracing. In order to activate very swallow depths we decreased the bombarding energy to the “linear” region of the cross-section curve. The disadvantage of the method is that the wear curve will be “linear” near to the surface instead of “constant” as is the case with the usual (high energy) TLA. The advantage is that the activity of the sample will be much lower and it is concentrated in the swallower studied depth. The other possible method is irradiation under small angle (15 to 30° or even grazing incidence), which also causes a near-surface concentration of the activity produced. Both methods are demonstrated with the most suitable nuclear reactions and some commonly used industrial materials.     

Isotopic ion exchange separation of radioisotopes using an acetone-water-hydrochloric acid system

Isotopic ion exchange for the rapid separation of radioactive mixtures has been further extended through the use of an acetone-water-hydrochloric acid system. Distribution data were obtained for 27 elements in the range of 15–90% acetone, 0.3N HCl indicating a number of new separations. The approach was used for the separation of several radioisotopes from short half-life magnesium matrix for activation analysis. The separations were completed in less than 5 minutes. Research supported by the Advanced Research Projects Agency.     

Cyclic neutron activation analysis for determination of selenium in food samples using <Superscript>77m</Superscript>Se

Cyclic neutron activation analysis method was conducted for determination of Se in food samples. High accuracy and good precision were proved by analyzing certified reference materials (CRMs) of chicken (GBW10018), rice (GBW10010) and cabbage (GBW10014). The detection limits for the three CRMs reached 0.16, 0.66 and 1.2 ng after 6 cycles at the 161.9 keV γ-peak from ^77mSe, under a neutron flux of 9.0 × 10¹¹ n cm⁻² s⁻¹ and the conditions of 30 s irradiation, 2 s decay, 30 s counting and 2 s waiting, significantly lower than those of conventional neutron activation analysis without any cycles, which were 0.94, 3.6 and 4.3 ng, respectively.     

Arsenic speciation: HPLC followed by ICP-MS or INAA

Sensitivities for the measurement of four arsenic species, As^III, As^V, monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), in environmental waters and rice extracts by a new neutron activation analysis (NAA) method using pre-separation of the species by liquid chromatography were determined. A manual fraction collection was used to isolate the species, followed by instrumental neutron activation analysis procedures. The sensitivities determined for arsenic species in the samples varied from 1.21 to 1.47 ng per vial or about 30 μg·L⁻¹ in sample solutions which translates to about 900 ng arsenic per gram of rice for our HPLC-NAA experiments.     

Hydride formation rates of B.C.C. group V metals

The group V b.c.c. metals generally require extensive activation procedures (e.g. heating to 300–500 °C and undergoing several absorption-desorption cycles) before they react with hydrogen at appreciable rates. We found that the solution of small amounts of a second metal yields alloys which will react extremely rapidly with hydrogen at room temperature without activation. The second metal should have a radius which is at least 5% smaller than that of the solvent group V metal.     

The effect of mechanical activation on the thermal reactions of P2O5–Al2O3–Fe2O3–Na2O phosphate glasses

The effect of mechanical activation on the structure and thermal reactions of glasses has been studied on the example of Na–Al–Fe phosphate glasses. These glasses are used in nuclear technology for immobilization of radioactive waste. The glasses were activated by grinding in a planetary mill. Mechanical activation causes a decrease of the T _g temperature as well as of the glass crystallization temperature. The type of crystalline phases formed and the quantitative proportions between them are changing. Analysis of inter-atomic interactions in the structure of glass was applied to explain the observed regularities governing the crystallization of the activated glasses.