Epithermal neutron activation analysis using the monostandard method

A method is described for epithermal neutron activation analysis of 17 elements in granite rock samples using a single standard. Gold has been used as a single comparator due to its relatively high resonance integral value (I₀=400 barn). In addition, it is preferable to Co in order to obtain a large epithermal activation in a short irradiation. The method of calculation is simple and rapid and can be done using a small calculator. Epithermal activation is able to overcome the difficulty arising from changing irradiation position as well as increasing the number of determinable elements by eliminating the interference from undesired isotopes which have relatively high thermal cross section values (₀), when reactor neutron flux is used. The coupling of epithermal activation with the monostandard method has the advantage of using a small Cd-cover which overcomes most of the difficulties arising in the relative method with large volume cadmium filters.     

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.     

Examination of the modified monostandard method in neutron activation analysis

The reproducibility, the small scale as well as the large scale variability of¹³⁷Cs extracted sequentially from the soil by using a modified Tessier procedure was investigated at several grassland sites in Bavaria/Germany and in the Chemobyl area. Because undisturbed grassland soils are never homogeneous with respect to their soil properties, all sequential extractions at the German sites were carried out at each plot separately for different soil layers (e.g., 0–2, 2–5, 5–10, 10–15, 15–20 and 20–30 cm). The results show that the coefficients of variation (CV) for the reproducibility of the extraction procedure for¹³⁷Cs was (with some exceptions) around 10–20% for all fractions. For the small scale variability of¹³⁷Cs (samples within an area of 10×10m²) the values for theCV were (again with a few exceptions) in the same range. Compared to that, the large scale variability of extractable¹³⁷Cs (random soil samples within an area of 100×200 km²) was higher for all fractions, even though only moderately. The implications of these results with respect to a sampling design are discussed.     

An application of the monostandard epithermal neutron activation technique for the analysis of domestic phosphate ores

The trace elements As, Co, Eu, Ga, La, Sb, Sc, Sm, U and W and the major constituents Fe and Na were determined in four domestic phosphate rocks by the monostandard epithermal neutron activation technique. Samples of 0.1 g were irradiated in the Egyptian 2 MW ERR-1 reactor under Cd cover, and the induced gamma activities measured after 6 h, 7 d and 8 w with a Hp Ge detector coupled to a computerized multichannel analyzer. Uranium has been used as a monostandard due to its relatively high resonance integral value (I₀=274.6 b) and because it is one of the elements to be determined more accurately. The present data are compared with those obtained by instrumental neutron activation analysis (INAA) method performed at Institute of Radiochemistry, Karlsruhe. The observed discrepancies do not exceed 12% in average. The present method is a practical alternative for trace element analysis.     

Determination of silver using cyclic epithermal neutron activation analysis

A fast pneumatic transfer facility was installed in Nuclear Engineering Teaching Laboratory (NETL) of the University of Texas at Austin for the purpose of cyclic thermal and epithermal neutron activation analysis. In this study efforts were focused on the evaluation of cyclic epithermal neutron activation analysis (CENAA). Various NIST and CANMET certified materials were analyzed by the system. Experiment results showed ¹¹⁰Ag with its 25 s half-life as one of the isotopes favored by the system. Thus, the system was put into practical application in identifying silver in metallic ores. Comparison of sliver concentrations as determined by CENAA in CANMET certified reference materials gave very good results.     

Neutron activation analysis by the monostandard method

The “absolute” quantitative processing of complex gamma-ray spectra has been made possible by the use of high resolution detectors and by irradiation with a well thermalized neutron flux. So, the simultaneous determination of many stable elements, either major or trace components is possible without destruction of the sample. The results of measurements on the irradiated samples show a threefold recurrence: (1) each element appears as often as it possesses activable isotopes, under the form of ray emitting nuclides, (2) each nuclide is determined as often as it presents ditinct emission lines, (3) all measurements are repeated in time. So under these conditions and with an original computer data processing, neutron activation analysis is a powerful analytical tool. The recurrence of the results gives access to the interpretation of the origin of various errors which consequently are better estimated. If applied to the study of ancients ceramics, this method should perhaps allow to evaluate the relationship between the geochemical imprint characteristic of the artifact and the original location, or even workshop.     

Multi-elemental epithermal neutron activation analysis using an internal single comparator

Epithermal neutron activation analysis using an internal single comparator has been used for the analysis of Saudi Arabian iron ores. The concentration of thorium, barium, terbium, tantalum, cobalt, lanthanum and antimony was determined using iron in the ore as an internal comparator for all the elements. In case of antimony there was an agreement between this method and the conventional method indicating that the given method is accurate.     

The monostandard method in thermal neutron activation analysis of geological, biological and environmental materials

Summary A simple method is decribed for instrumental multielement thermal neutron activation analysis using a monostandard. For geological and air dust samples, iron is used as a comparator, while sodium has advantages for biological materials.To test the capabilities of this method, the values of the effective cross sections of the 23 elements determined were evaluated in a reactor site with an almost pure thermal neutron flux of about 9·10¹² n·cm^–2·s^–1 and an epithermal neutron contribution of less than 0.03%. The values obtained were found to agree mostly well with the best literature values of thermal neutron cross sections. The results of an analysis by activation in the same site agree well with the relative method using multielement standards and for several standard reference materials with certified element contents. A comparison of the element contents obtained by the monostandard and relative methods together with corresponding precisions and accuracies is given.

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Die Monostandardmethode bei der Aktivierungsanalyse mit thermischen Neutronen von geologischem, biologischem und Umweltmaterial

Zusammenfassung Die Monostandardmethode wurde erstmals auf die Aktivierungsanalyse mit rein thermischen Neutronen aus der thermischen Säule des Reaktors FRJ-2 (mit epithermischen Anteilen von < 0,03%) angewendet. Hier sind die theoretischen Verhältnisse und damit auch Gleichungen besonders einfach. — Die bei einem Neutronenfluß von 9·10¹² n·cm^–2·s^–1 ermittelten effektiven Neutroneneinfangquerschnitte stimmen häufig gut mit den Literaturwerten überein. — Für geologische Proben wurde Eisen, für biologisches Material Natrium als Komparator, d.h. Monoelementstandard, verwendet. Es konnten über zwanzig Elemente in Andesit, Granit, Flugstaubasche, Luftstaub, Pflanzenmaterial und Obstblättern bestimmt werden.

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Dedicated to Professor Dr. Kurt Starke, University of Marburg/ Lahn on the occasion of his 70 th birthday

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Fourth Communication on Improvement of Instrumental Analysis for Service Analysis

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Guest Scientist from Egypt.

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Guest Scientist under IAEA-Fellowship from the Faculty of Chemistry, University of Sofia, Bulgaria

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This paper is an extract of the more detailed Report Jül-1822 (ISSN 0366-0885), January 1983.     

The epithermal neutron flux distribution in a nuclear reactor and its effect on epithermal neutron activation analysis

The shape of the epithermal neutron energy distribution has been determined in two irradiation positions of the University of London CONSORT II reactor. The method applied involves cadmium ratio measurements using a series of resonance detectors. Principles of the method and some considerations relative to epithermal neutron activation analysis in connection with the deviation of the epithermal neutron flux distribution from the 1/E law are given.     

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 determinations in ground water ultrafiltrates using inductively coupled plasma mass spectrometry and monostandard neutron activation analysis

Twelve ultrafiltrates of two ground waters rich in humic substances (up to 97.8 mg CL^–1) and in salinity (up to: cations 44.3 meq L^–1, anions 44.9 meq L^–1) were investigated with ICP-MS and with NAA in parallel. With both techniques 22 elements were analysed in a wide concentration range (mg/L to ng/L). Ultrafiltration at pore sizes from 1000 nm down to 1 nm lowers the humic colloid content as well as the concentration of the colloidborne polyvalent cations. Carbon interferences were studied in detail using artificially prepared model waters. The detection limits of ICP-MS in the ultrafiltrates (0.01 g/L–10 g/L) and in pure analyte solutions (5 ng/L–600 ng/L) are compared with those of NAA for pure water analysis (0.004 ng/L–50 ng/L).Dedicated to Professor Dr. H. Schmidbaur on the occasion of his 60th birthday     

Determination of bromine and iodine in biological and environmental materials using epithermal neutron activation analysis

Epithermal neutron activation analysis (ENAA) was applied to the determination of the contents of bromine and iodine in 40 biological and environmental standard reference materials and Chinese diets. Boron nitride (BN) for solid samples and BN+Cd for liquid samples were adopted as shield material. Irradiation was carried out in inner and outer irradiation sites in a Miniature Source Reactor (MNSR) for solid and liquid samples, respectively. The 443 keV photopeak of ¹²⁸I and the 616 keV photopeak of ⁸⁰Br were used. The precision of measurement (relative standard deviation) is 2∼6% for contents of iodine of more than 100 ng/g and 8∼12% in the 20∼100 ng/g range in solid samples, and 12∼18% at less than 100 ng/ml in liquid samples. For bromine, the precision of measurement is 2–8% for solid samples and lower than 13% for liquid samples. The detection limits under experimental conditions varied between 10∼30 ng/g, 55∼95 ng/g and 25∼68 ng/g for iodine and 50∼150 ng/g, 200∼450 ng/g and 100∼300 ng/g for bromine in ENAA with BN shield in inner irradiation sites, with Cd shield and BN+Cd shield in outer irradiation sites, respectively. Received: 13 June 1996 / Revised: 2 September 1996 / Accepted: 19 September 1996     

Trace multielement analysis in boron materials by epithermal neutron activation analysis

A method, based on epithermal neutron activation analysis using a boron filter is described for the determination of ～60 trace elements in boron and its compounds. The method has an accuracy of ～20%, a precision of ～15% RSD and limits of detection for most elements are either at the sub-ppm or low ppm levels. The method requires no sample preparation and is economical in effort.     

Investigations on the comparator technique used in epithermal neutron activation analysis

The possible extension of the comparator technique of reactor neutron activation analysis into the field of epithermal neutron activation has been investigated. Ruthenium was used for multi-isotopic comparator. Experiments show that conversion of the so-called reference k-factors—determined by irradiation with reactor neutrons—into k_epi-factors usable at activation under cadmium filter, can be evaluated with fair accuracy. Sources and extent of errors and their contribution to the final error of analysis are discussed. Based on the paper presented at the 2nd European Conference on Analytical Chemistry, 25–30 August, 1975, Budapest, Hungary.     

Multielement analysis of Chinese Biological Standard Reference Material by monostandard instrumental neutron activation analysis

A procedure for monostandard INAA of 21 elements (Hg, As, Br, Cr, Sb, Se, Ba, Zn, Ca, Ce, Co, Cs, Eu, Fe, Hf, K, La, Rb, Sc, Sr, Ta) in Chinese Biological Standard Reference Material (peach leaves) is described. The accuracy of the procedure was checked by analyzing the U.S. NBS Standard Reference Materials SRM-1571 and SRM-1632a.     

Analysis of foods for iodine by epithermal neutron activation analysis

Epithermal-neutron activation analysis (ENAA) was applied to the analysis of foods for iodine. The procedure involves irradiation of wet foods in a boron nitride, vessel, followed by direct counting of the 442.9 keV gamma ray of¹²⁸I without any processing of the sample. Three research reactors were evaluated for use in determining iodine by ENAA. The University of Virginia reactor at Charlottesville was chosen for this study because the reactor facilities minimized thermal heating of the boron nitride vessel, enabling irradiation of larger, more representative analytical portions. Iodine concentrations ranging from <0.003 to 0.74 g/g are reported for 17 different food matrices.     

Detection limits in epithermal neutron activation analysis of geological material

The improvement of detection limits for trace elements in geological samples by epithermal neutron activation analysis is examined. The relative merits of cadmium, boron and composite cadmium+boron filters are compared for trace elements Ni, As, Pd, Cd, Sb, W, Ir, Pt and Au, and interfering elements Na, K, Sc, Cr, Fe, Co and Cu. A boron filter gives optimum sensitivity for the trace elements based on interference from⁴⁶Sc, but the detection limits are only improved 2–5 times. Ma imum possible improvement, which is shown by Ni, gives sensitivities 5 times better under cadmium and 15 times under boron.     

A technique for reducing interferences in epithermal neutron activation analysis

A new epithermal neutron activation technique is described. The technetium is based on the existence of non-overlapping resonance peaks in the neutron absorption cross-section spectra for the nuclides present in the sample to be analyzed. By this method it is possible to reduce some of the interfering activities with respect to the sought activity by using appropriàte filters. An experiment has been carried out to demonstrate the validity of the technique.     

Uranium in coral skeletons determined by epithermal neutron activation analysis

A simple and non-destructive method has been proposed for the routine determination of uranium by epithermal neutron activation analysis in coral skeletons. Using a cadmium capsule, about 0.1-0.2 g samples were irradiated for 6 hours in the Triga Mark II Reactor. Measurements of -ray (²³⁹Np via ²³⁹U) were performed with each sample and standard after cooling for about three days. Compared with a non-destructive thermal NAA, the present method was found to improve the sensitivity because it reduced the intense Compton background induced by ²⁴Na. We determined uranium in coral standards within 2% of analytical precision. The data obtained for the carbonate standards are mostly consistent with reported values. The present method could be usefully applied to determine uranium contents in fossil corals from the Funafuti Atoll in the Pacific. The distribution of uranium between seawater and coral skeletons is also discussed in order to understand the environmental media in which the coral grew.     

Trace element analysis of biological materials by thermal and epithermal neutron activation analysis

A scheme for instrumental neutron activation analysis of biological materials is proposed. The scheme is based on a combination of thermal and epithermal activation. The accuracy is evaluated by analyzing 4 standard reference materials. Results from the analysis of human blood serum and plasma are given.