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.     

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.     

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.     

Error estimation of the single comparator method due to uncertainties of literature data for thermal and epithermal neutron activation cross-sections

The reliability of the single comparator method depends mainly on the accuracy of k factors. This paper describes error in theoretical k factors, especially that due to the scattering in literature data for thermal and epithermal neutron activation cross-sections. Error calculations were performed for thirteen elements using comparator sets of⁶⁰Co−¹⁹⁸Au and⁹⁵Zr−⁹⁷Zr to evaluate the accuracy of this method.     

Multi-element analysis of japanese tea leaves by neutron activation analysis and the single comparator method

The reliability of the single comparator method in neutron activation analysis has been studied by comparing the calculated and experimental k values and by determining the concentration of trace elements in iron. The method has been applied to the analysis of tea leaves for thirteen elements; their concentrations varied over five orders of magnitude.     

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.     

Reactor neutron activation analysis by a triple comparator method

The single comparator method has been extended to a triple comparator method, using⁶⁰Co,^114m In and¹⁹⁸Au. In this technique, thek-ratios of the elements to be analyzed, now determined against the three comparators, are corrected for each new ratio of thermal to epithermal reactor neutron flux. These flux ratios are calculated from the absolute activities of the three comparators. The thermal neutron activation cross-section and the resonance integral for the reaction¹¹³In(n,γ)^114m In have been determined.     

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.     

Prompt-gamma neutron activation analysis using an isotopic neutron source

This paper describes an experimental set up using an isotopic neutron source with graphite, preferably to a hydrogen-rich compound, as moderator. This low thermal flux source has been employed in PGNAA experiments. Only those elements having a high cross section can be quantitatively analyzed at low concentration levels, mainly, Gd, Cd, Sm, B and Hg; the other elements can only be probed at macroscopic levels. An application to the determination of boron content in collyria examplifies the possibilities of the technique.     

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.     

Instrumental neutron activation analysis of silicon wafers using the silicon matrix as the comparator

For the instrumental neutron activation analysis of trace impurities in high purity silicon wafer, a modified single comparator method has been applied. The energy distribution of the neutrons at the irradiation position was measured using the two flux monitors, Au and Co, and elemental contents were calculated using the silicon matrix in the wafer as a comparator. This has advantage of reducing the cross contamination from an external monitor during sample preparation and irradiation, the uncertainties from the non-homogeneity of the neutron flux and the error on the weight of comparators. Determination limits for 49 elements were presented under the condition of 72 hours irradiation at a neutron flux of 3.7·10¹³ n·cm^-2·s^-1 and 4000 s measurement. The analytical results obtained by this method and the conventional single comparator method were compared and were found to agree well within 5%.     

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.     

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     

Determination of iodine in human nails via epithermal neutron activation analysis

An epithermal instrumental neutron activation analysis (EINAA) method, using a boron nitride irradiation capsule compatible with use in the University of Missouri Research Reactor pneumatic-tube irradiation facility, has been developed for the analysis of iodine in human nails. The principal objective was to determine if the nail could be used as a means of monitoring dietary intake of iodine. The EINAA method was used to analyze nails from subjects having iodine intakes that could be qualitatively differentiated. Iodine concentrations in nails from these subjects were positively correlated with apparent iodine intake.     

Silicon determination in plant materials by instrumental epithermal neutron activation analysis

The Si determination with epithermal neutrons using the reaction²⁸Si (n,p)²⁸Al is described. Thermal neutrons are eliminated from the irradiation position with a BN-shield. Two first order interfering reactions with P and with Al necessitate appropriate corrections. The interfering reaction on Al is shown to depend heavily on the hydrogen (H) content of the sample, which therefore must be taken into account. The lower application range in plant samles is estimated to be 500 g g^–1. Reproducibility is <5% in suitable cases, but not as good if the necessary corrections are large. The capacity is 25 samples per 8 h. The method is applied to 3 plant standards (rice, hay and pine needles) and to 47 samples of spruce needles. The applicability to different plant materials is mainly limited by their relative Al, P and Si concentrations. Literature values are use to find plant categories in which Si can be reasonably determined by instrumental epithermal neutron activation analysis (IENA).     

Estimates of iodine in biological materials by epithermal neutron activation analysis

Iodine abundances in NBS biological SRMs and various organs of rats were evaluated by epithermal neutron activation analysis with a boron carbide filter. Detectability of iodine in different biological materials by this method is discussed.

     

Examination of Greek neolithic ceramic shards by epithermal neutron activation analysis

At the reactor of the NCSR “Demokritos” epithermal irradiation was used in connection with a loss-free counting technique to investigate rare Neolithic ceramic shards, about 4000 years old, from the Alepotrypa Cave of Diros, Greece. The application of an irradiation time of 30 minutes, the measurements of the samples after less then 24 hours and a counting time of 20 minutes in connection with a loss-free counting unit allowed the determination of 12 elements per sample. The comparison of these rare fine ceramic shards with those of primitive shape showed that both were produced from the same raw materials. Small differences could be explained by a raw material pretreatment. The Neolithic potters were obviously aware of separation techniques in order to obtain fine clay fractions to produce those rare ceramics.