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.     

Thermal and epithermal neutron activation analysis using the monostandard method

A new approach is presented for neutron activation analysis using the monostandard (single comparator) method. Elements to be determined are classified into two groups; those with σ_o>I_o are activated with whole neutron spectrum (without Cd-cover), using a standard of the same group (e.g. Sc), while elements with I_o>σ_o are activated with epithermal neutrons (under Cd-cover) using a standard of the same group (e.g. Au or Co). Epithermal activation increases the number of determinable elements and its coupling with the monostandard method has the advantage of using a small Cd-cover. The σ_o and I₀ values of some elements were determined to test this approach.     

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.     

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.     

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.     

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.     

Rapid analysis of biological reference materials by instrumental neutron activation

Summary Instrumental neutron activation analysis (INAA) was applied to the rapid determination of cadmium and other elements in the IAEA biological reference material horse-kidney (H-8). Nuclear reactor neutrons and epithermal neutrons were used as neutron sources. Cadmium, bromide, iodine and phosphorus were determined by epithermal neutron activation analysis. Aluminum was determined by reactor neutron activation analysis taking into account the contribution of phosphorus to the ²⁸Al activity.     

Epithermal neutron activation analysis and its application in the Miniature Neutron Source Reactor

The cadmium and boron ratios from 44 elements, totally 66 nuclides, were determined in the inner and outer irradiation sites of the Miniature Neutron Source Reactor (MNSR). China Institute of Atomic Energy. A permanent Cd-shielded epithermal neutron irradiation site has been designed and installed in the outer of the beryllium reflector of this reactor. Elements e.g., I, Br, Sr, Si, Th and U in biological samples, such as foodstuff, water and blood, geological and environmental samples, such as soil, rock, sediment and vegetable leaves were analyzed by BN-shielded epithermal neutron activation analysis (ENAA), and Au, As, Sb, Th and U by Cd-shielded ENAA. The results show that the detection limits of these elements by ENAA are better by a factor of 1.5–7 than those with conventional NAA.     

Intercomparison and determination of environmental standard samples by instrumental neutron activation analysis

To identify and improve the analytical technique for air pollution research, four kinds of environmental standard samples, i.e., airbome particulate matter, coal flyash, soil and pine needle supplied from the NIST and the IAEA were analyzed using thermal and epithermal neutron activation techniques. Sample irradiation was done at the irradiation facilities (neutron flux, 1 · 10¹³ n·cm^–2·s^–1) of the TRIGA MARK-III Research Reactor in the Korea Atomic Energy Research Institute. The accuracy and precision for the analysis of 40 trace and toxic elements in the samples were compared with the certified and reported values, respectively. In the analytical results of all standard reference materials, the relative standard deviation were within the 15% except for 11 elements and the relative error were agreed within the 10–20% except for 13 elements. The benefit of epithermal activation was investigated and the optimum analytical condition is reported.     

Evaluation of soil to tea plant elemental correlation using instrumental neutron activation analysis

Instrumental neutron activation analysis using relative and k ₀-based internal monostandard methods were employed for determination of concentrations of 12 elements in soil and tea plants collected from three different tea producing regions in India namely Assam, Darjeeling and Kangra. A total of 17 tea leaf samples along with corresponding soil samples were analyzed for elemental content. The obtained concentration data was used for the soil–plant elemental correlation studies. Positive correlation was observed between elemental concentrations of tea plants and the associated soil with Pearson correlation coefficient values in the range 0.6–0.9 for ten elements. Variations in transfer factor values were also observed according to the geo-chemical variation.     

Advantage factors in optimized instrumental neutron activation analysis of some biosphere samples

The best conditions for the instrumental neutron activation analysis of some biosphere samples were determined by the numerical simulation of γ-ray spectra of samples of the specified composition. Certified reference materials of soil (SO-1 ), tobacco leaf (STA-OTL-1 ), carbon dust (FFA-1 ), and river (JSD-1 ) and lake (JLK-1) precipitates were used as test samples. The efficiency of the proposed procedure was demonstrated using advantage factors, which are expressed in terms of the signal-to-background ratio calculated by the proposed and conventional procedures     

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.     

Inteferences in neutron and photon activation analysis

The effect of following interferences was quantitatively assessed in terms of interference factor by irradiating samples together with highly pure reagents at two reactor sites of diferent neutron spectra and fluxes for neutron activation analysis (NAA) and an electron LINAC for photon activation analysis (PAA). The interfering reactions studied are 91) fast neutron-induced reactions, (2) uranium fission (3) (n,γ) reactions of other target elements in NAA, and (4) reactions induced by secondary neutrons in PAA. Corrections for these interferences were successfully applied to the activation analysis of some geological reference rock samples and biological samples.     

Trace element determination in high-purity aluminum clad samples by k 0-based internal monostandard instrumental neutron activation analysis

The k₀-based internal monostandard instrumental neutron activation analysis (IM-INAA) method was applied for quantification of trace impurities in seven high purity aluminum samples used as fuel cladding in a research reactor. Samples along with BCS CRM 182 (Si–Al alloy) were irradiated in high flux reactor neutrons for 10–15 h. In situ detection efficiency, needed in concentration calculation ratio by IM-INAA, was obtained using gamma rays of activation products produced in the samples. Elemental concentration ratios obtained with respect to Fe (used as internal monostandard) were converted to absolute concentrations by determining concentration of Fe by relative method of NAA. Concentrations of ten trace elements (Sc, Cr, Co, Zn, Ga, La, Ce, Sm, W and Hf) including major element Fe were determined in this work. The method used is non-destructive in nature and does not need multielement standards. Results of IM-INAA were compared with those obtained by relative method of INAA and inductively coupled plasma atomic emission spectrometry (ICP-AES). Details of methodologies and results obtained by all methods are discussed and compared in the paper.     

Large sample neutron activation analysis of dross for gold and silver

Large sample neutron activation analysis of dross from India Government Mint, Mumbai was carried out for quantification of gold (Au) and silver (Ag) using graphite reflector position of Advanced Heavy Water Reactor critical facility at Bhabha Atomic Research Centre, Mumbai. The k ₀-based internal monostandard NAA was used to calculate concentration ratios of Au and Ag with respect to sodium (Na), which was used as an internal monostandard. The concentration ratio values of Au to Na of varying mass of dross showed that mass ≥2 g was the representative sample size for analysis. Concentrations of gold and silver were found to be in the range of 200–400 and 1200–1700 mg kg^?1, respectively in three different samples.     

Large sample neutron activation analysis of municipal solid waste using shutdown MNSR photoneutrons

Waste material in many cases may contain hazardous substances. Therefore, it requires appropriate classification. Large sample neutron activation analysis (LSNAA) can be adapted for the screening of such materials. LSNAA of municipal solid waste utilizing shutdown MNSR photoneutrons was performed in this work using internal monostandard technique. Good agreement was obtained between the results of this method and that of standard comparative one. This work allows extending the reactor utilization period by using its irradiation sites during shutdown state as low neutron flux irradiation facility for LSNAA.     

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.     

Serum aluminum determination by instrumental neutron activation analysis in long-term haemodialysis patients

Serum aluminum levels were determined by instrumental neutron activation analysis in 31 patients undergoing long-term haemodialysis. Aluminum-28 1.778 MeV (T _1/2=2.24 min) γ-rays produced by the thermal neutron reaction²⁷Al(n,γ)²⁸Al were detected. Successive irradiation of the samples at epithermal neutron fluence was performed to correct for the interference from the fast neutron reaction³¹P(n,α)²⁸Al. Serum aluminum level in this group of subjects was adequately represented by a lognormal distribution with a mean and variance of 16.5 μg/l and 16.8 μg/l, respectively. The results obtained were found to be in agreement with serum aluminum determination performed by electrothermal atomic absorption spectrophotometry (r ²=0.97). Instrumental neutron activation can provide a rapid technique to routinely monitor long-term haemodialysis patients in order to identify individuals at greater risk to develop aluminum toxicity.     

Determination of trace elements in water by non-destructive neutron activation

A systematic study was undertaken in order to find out which of the most relevant elements can be determined in water under normal conditions by non-destructive neutron activation simultaneously using a suitable monostandard method. Standardized water samples as well as natural water of different kind were used, brought to dryness by freeze-drying and irradiated in quartz at a neutron flux of 10¹⁴ cm⁻² s⁻¹ for 1 day. The trace element content in quartz ampoules of different origin was determined separately. The following elements are discussed in detail including possible interferences: As, Au, Br, Ca, Cd, Co, Cr, Cu, Eu, Fe, Hg, K, La, Mo, Na, Ni, Sb, Sc, Se, U, Zn. Presented at the Euroanalysis II Conference, Budapest, 25–30. Aug. 1975.     

Monte Carlo calculations and neutron spectrometry in quantitative prompt gamma neutron activation analysis (PGNAA) of bulk samples using an isotopic neutron source

An activation analysis facility based on an isotopic neutron source (185 GBq ²⁴¹Am/Be) which can perform both prompt and cyclic activation analysis on bulk samples, has been used for more than 20 years in many applications including 'in vivo' activation analysis and the determination of the composition of bio-environmental samples, such as, landfill waste and coal. Although the comparator method is often employed, because of the variety in shape, size and elemental composition of these bulk samples, it is often difficult and time consuming to construct appropriate comparator samples for reference. One of the obvious problems is the distribution and energy of the neutron flux in these bulk and comparator samples. In recent years, we have attempted to adopt the absolute method based on a monostandard and to make calculations using a Monte Carlo code (MCNP4C2) to explore this further. In particular, a model of the irradiation facility has been made using the MCNP4C2 code in order to investigate the factors contributing to the quantitative determination of the elemental concentrations through prompt gamma neutron activation analysis (PGNAA) and most importantly, to estimate how the neutron energy spectrum and neutron dose vary with penetration depth into the sample. This simulation is compared against the scattered and transmitted neutron energy spectra that are experimentally and empirically determined using a portable neutron spectrometry system. This revised version was published online in August 2006 with corrections to the Cover Date.