Determination of the contents and distribution characteristics of REE in natural plants by NAA

The concentration of 8 REEs (La, Ce, Nd, Sm, Eu, Tb, Yb and Lu) in 17 species of plants and their host soil, which were collected from a rare earth ore area located in the south of China, have been determined by INAA. The chondritic normalized REE patterns for different parts of plants (e.g., leaf stem and root) and their host soils were studied. The results showed that the concentration levels of REE for most plants in the sampling area were elevated. Particularly, the leaves of the fern (Dicranopteris dichotoma) contain extremely high concentration of the total REE (675–3358 g/g) Generally, these REE distribution patterns in every part of plants were very similar and reflected the characteristics of their host soils. However, the chondritic normalized REE patterns in some plants relative to the host soil revealed obvious fractionation, such as the depletion of the heavy REE (for fernCitrus reticulata andBrassia campestris), the heavy REE enrichment (forCamellia sinensis, Camellia oleifera andZiziphus) and the Ce positive anomaly (forGardenia jasminoides).     

Multielement analysis by sequential instrumental and radiochemical neutron activation

We measured 37 elements in six USGS geological camples and one NBS biological orchard leaf (OL) sample, using sequential INAA and radiochemical group separation coupled with high resolution, high efficiency Ge(Li), and a Ge(Li) with anticoincidence shields. The elemental concentrations in these samples vary over three orders of magnitude. Our results agree very well with the reported values. The rare earth values in PCC-1 are 2–4 times lower than the reported values. Precise REE patterns are defined in USGS samples, which are characteristic of the total rock types. The REE pattern in OL is identical to the mineral apatite. In addition to the possibility that OL may be contaminated by local soil, it is also possible that the uptake of REE trace elements by plants from soil is perhaps dominated by accessory mineral such as apatite, or plants take up the REE from bulk soil in a preferential manner as a smooth function of the REE ionic radii.     

Neutron activation analysis of the rare earth elements in rocks from the earth's upper mantle and deep crust

Three techniques for analyzing rare earth elements (REE) in geological materials are described, i.e. instrumental neutron activation analysis (INAA), neutron activation analysis with pre-irradiation chemical REE separation (PCS-NAA) and radiochemical neutron activation analysis (RNAA). The knowledge of REE concentrations in eclogites, peridotites and minerals from the earth's lower crust and upper mantle is very useful in constraining their petrogenetic history.     

Determination of rare earth elements in carbonatites from the Kangankunde Mine, Malawi by instrumental neutron activation analysis

Nine rare earth elements (REEs) in African carbonatite samples were determined by instrumental neutron activation analysis (INAA). The geochemical behavior of REEs in carbonatites, especially REE pattern (chondrite-normalized), is studied in relation to carbonatite formation at the Kangankunde Mine, Malawi. REE-rich phosphate minerals, particularly monazite, and the other unusual minerals such as strontianite, are observed during the stages of carbonatite formation. Four kinds of carbonatites exhibit similar chondrite-normalized REE distribution patterns in spite of the marked difference of their REE contents. All these carbonatites are characterized by the strong fractionation between light and heavy REEs and by the very high La/Yb ratio (1000-2800).     

Determination of rare earth and other trace element abundances in human kidney stones and brain tissue by instrumental neutron activation analysis

We have used INAA to analyze more than 30 minor and trace elements in 10 human kidney stones (phosphate and oxalate types). In addition we also analyzed human brain tissue samples for trace elements by INAA to determine the limitations of the method. Samples were taken from the temporal and frontal cortex of the brain of a patient that suffered from dialysis encephalopathy (where an increased Al content is expected), as well as a number of control samples. Trace elements were analyzed to study possible compositional differences other than the Al content. The analyses were done using large volume HPGe detectors; because of the low abundances, accuracy and precision vary between 3–80% for individual elements. We found a difference between the rare earth element (REE) patterns for apatite and oxalate kidney stones, and a fractionation compared to typical REE contents in plants. For the brain samples there is evidence for differences between the dialysis patient and the control samples not only for Al, but also for some other elements including the REEs, but most differences are minimal, and may not be significant.     

Rare earth element patterns in biotite muscovite and tourmaline minerals

Rare earth element concentrations in the minerals biotite and muscovite from the mica schist country rocks of the Etta pegmatite and tourmalines from the Bob Ingersoll pegmatite have been measured by INAA and CNAA. The concentrations range from 10^–4 g/g to 10^–10 g/g. The REE patterns of biotite, muscovite and tourmaline reported herein are highly fractionated from light to heavy REE. The REE concentrations in biotite and muscovite are high and indigenous. The pegmatite tourmalines contain low concentrations of REE. Variations in tourmaline REE patterns reflect the geochemical evolution of pegmatite melt/fluid system during crystallization.Work supported by the U. S. Department of Energy under Contract DE-AC06-76RLO 1830.     

Determination of rare earths and other trace elements in samples of Antarctica by neutron activation analysis

The concentrations of REE and other trace elements have been determined in samples of Antarctica by Instrumental Neutron Activation Analysis (INAA). The samples were collected from the West Lake area near Great Wall Station. The samples include sediment, residual plants, rock and soil taken from the bottom of the lake to 3.4 m deep. The amounts of samples were very rare. In order to get more information, reactor NAA using both short and long irradiations with K₀ standardization has been adopted. Nine rare-earth elements (REE) namely La, Ce, Nd, Sm, Eu, Tb, Dy, Yb, and Lu as well as other trace elements (As, Au, Ba, Br, Co, Cr, Hf, Sc, Se, Th, V, Zn) have been determined. The concentrations and distribution patterns of REE in the samples have been given.     

The use of pre-irradiation group separations with neutron activation analysis for the determination of the rare earths in silicate rocks

The radiochemical neutron activation technique used consists of five stages; viz. sample digestion, cation exchange chromatography, irradiation and counting. Silicate samples are decomposed using a conventional hydrofluoric/perchloric acid digestion followed by loading the solutions, as chlorides, onto cation exchange resin columns. The columns are eluted with 2M HCl to remove unwanted elements and the rare earth elements are subsequently desorbed with 6M HCI. A tracer,¹⁴⁴Ce, is used to monitor the chemical yields and studies show that no fractionation or loss of any REE occurs. The REE abundances of five reference samples (NIM-G, SY-2, MRG-1, JB-1 and BOB-1) show that the described procedure is capable of providing good accuracy and precision. The method has some advantages over conventional INAA and RNAA and these are described.     

Use of INAA,PGAA, and RNAA to determine 30 elements for certification of an SRM: Tomato Leaves, 157a

Analyses for certification have been made for the determination of 30 elements in the National Institute of Standards and Technology (NIST) Tomato Leaves renewal reference material, SRM 1573a. Three of the analytical techniques used were instrumental neutron activation analysis (INAA), radiochemical neutron activation analysis (RNAA), and prompt gamma activation analysis (PGAA). These techniques provided data on 19 elements by INAA, 10 elements by PGAA, and 7 elements by RNAA, with some overlap between techniques. For example, INAA was able to obtain overall analytical uncerainties (at the 95% confidence level) averaging ±2.2% for major and minor constituents (Ca, Mg, K), ±3.3% for constituents from 1 to 1000 g/g (Na, Fe, Al, Mn, Ba, Zn, Rb, La, Cr), and ±6.4% for elements between 10 and 1000 ng/g (Co, V, Se, Th, Sc, Sb), using sample dry weights of approximately 150 mg. These analyses represent the most extensive use to date of nuclear analytical techniques in the certification of a trace element SRM at NIST.     

Non-destructive bone aluminum assay by neutron activation analysis

A non-destructive method based on instrumental neutron activation analysis (INAA) for the assay of aluminum in bone samples is described. The²⁸Al signal obtained upon neutron irradiation includes contributions from both the reaction²⁷Al(n,)²⁸Al and³¹P(n,)²⁸Al. The first reaction is with the thermal neutrons and the second one is with the fast neutrons. The contribution from the³¹P reaction is calculated from the fact that Ca/P ratio in bone mineral is constant and the amount of calcium can be measured from the thermal reaction⁴⁸Ca(n, )⁴⁹Ca. The aluminum values obtained by the INAA procedure agreed within 10% of those obtained by atomic absorption spectrophotometry. With this assay the levels of aluminum in normal bones (<70 g g^–1 apatite) cannot be determined reliably but higher aluminum levles in bone biopsies associated with Al toxicity, e.g. some patients with renal osteodystrophy, can be determined with a precision of ±10%.     

Thek 0 calibration of the IRI system for INAA of samples in the kg range

The feasibility of the INAA of samples in the kg range has been demonstrated in 1994 byOverwater et al. In his studies, however, he demonstrated only the agreement between the corrected -ray spectrum of large samples and that of small samples of the same material. In this paper, thek ₀-calibration of the IRI facilities for large samples is described, and some ofOverwater's results for homogeneous materials are presented again, this time in tems of (trace) element concentrations. It is concluded that large sample INAA can be as accurate as ordinary INAA.     

ICP emission spectrometric analysis of rare earth elements in permanent magnet alloys

An analytical method for the determination of rare earth elements (REE) in a NdFeB permanent magnet alloy by ICP emission spectrometry is described. Spectral interferences, arising from overlapping, as well as matrix effects have been studied. Considering spectral interferences, sensitivities of spectral lines, background intensities and the chemical composition of the sample investigated, optimum spectral lines for each REE have been selected. Because of an unfavourable concentration ratio in samples of a NdFeB permanent magnet alloy, a preliminary separation of matrix elements from rare earth elements by ion chromatography is necessary. Different modes of elution (isocratic and gradient) with -hydroxy-isobutyric acid and different columns (NUCLEOSIL, SULFOPROPYL SI-100, DIONEX HPIC-CS3) have been tested. Optimum separation conditions have been chosen for each element and the separation efficiency at equal or different concentrations of the selected elements have been established. Although the separation of REEs resulted in partly overlapping peaks, the ratio between analyte and interferent is improved and the spectral interferences are diminished. The results obtained are in good agreement with certified values.     

The effect of other activities on INAA limits of detection

The instrumental neutron activation analysis (INAA) Advance Prediction Computer Program (APCP) is described, as well as its areas of usefulness. Particular attention is devoted to its ability to predict g and ppm INAA lower limits of detection (LOD's) of any particular elements of interest in any sample matrix type of even very approximately known average or typical elemental composition. In general, INAA g LOD's are found to be 10 to 100 times higher than the corresponding interference-free values, and INAA ppm LOD's are found to be 100 to even 100 000 times higher than the corresponding interference-free values calculated for a one-gram sample.     

Multielement characterization of silicon carbide powders by instrumental neutron activation analysis and ICP-atomic emission spectrometry

Summary Instrumental neutron activation analysis (INAA) and inductively coupled plasma atomic emission spectrometry (ICP-AES) have been optimized for application to a comprehensive analysis of silicon carbide powders. Via medium- and long-lived indicator radionuclides with half lives between 2.3 h (¹⁶⁵Dy) and 12.4 a (¹⁵²Eu), INAA can detect 55 elements. Analytical parameters and experimental modes are given with limits of detection obtained for a silicon carbide powder of typical purity grade. For the performance of ICP-AES, a wet-chemical decomposition procedure was optimized for sample portions of about 1 g using a mixture of high-purity conc. HF, HNO₃ and H₂SO₄ for digestion in autoclaves with a PTFE-liner. For all investigated elements, recoveries 98% were obtained. By scanning wavelength profiles, interference-free emission lines were found for 56 elements. By the combined performance of INAA and ICP-AES, 66 elements were assayed in the analysed silicon carbide powder. The limits of detection were below 0.01 g/g for 24 elements, they were between 0.01 and 0.1 g/g for 17 and between 0.1 and 1 g/g for 15 elements. The remaining 10 elements were detectable at levels >1 g/g. The comparison of results of these two methods as well as of results obtained by other laboratories shows that, for the most common impurities, a satisfactory degree of accuracy could be achieved.     

Comparison of routine INAA procedures based on k0 and kZn standardizations

Performance characteristics (especially accuracy) of a routine INAA with k₀ standardization were verified and compared with those of INAA with a classical single comparator. For this purpose, samples of three certified reference materials of environmental origin (Fly Ash, Orchard Leaves and Buffalo River Sediment—all supplied by NIST) were irradiated with both kinds of comparators (Au–Zr for k₀ and Zn for classical k method) in one irradiation rabbit. Also the following steps of INAA procedure were practically the same for both standardization methods used (counting, spectral processing, etc.). The results have shown that the k₀ method gives sufficiently accurate results comparable with those of the well established and routinely used single comparator (Zn) method, provided proper neutron flux monitoring, efficiency calibration and also coincidence summing corrections are applied. This work shows that modern k₀ standardization method in INAA can be sucessfully used in routine practice and applied with an advantage in INAA laboratories subject to changes of neutron spectra or counting conditions.     

Determination of rare earth elements by neutron activation analysis in altered ultramafic rocks from the Akwatia District of the Birim diamondiferous field,Ghana

Summary Rare earth element (REE) analysis using instrumental neutron activation (INAA) was carried out on ultramafic rocks from the Akwatia District of the Birim diamondiferous field, Ghana, with the primary objective of investigating their kimberlitic characteristics. The total REE concentrations range from 113 to 1610 ppm and fall within the interval of those reported in the literature for kimberlites. Despite the marked difference in the REE contents, all the analyzed samples show similar REE patterns that resemble those of kimberlites. However, compared to most of the kimberlites, the ultramafic rocks have small negative Eu anomalies and low light-REE/heavy-REE ratios, suggesting that the rocks have been significantly assimilated by crustal rocks.     

Multi-element standard for routine instrumental activation analysis of trace elements in rocks and tectites

The use of high-resolution Ge(Li) detectors in non-destructive instrumental neutron activation analysis (INAA) of mineral materials makes possible the simultaneous determination of a number of trace elements. In routine applications of INAA the use of a multi-element standard (MES) has proved to have advantages over a set of standards for each determined element. An MES has been prepared containing 8 trace elements mixed in a suitable proportion and giving, after neutron activation, long-lived γ-emitters, the γ-ray lines of which regularly occur in the γ-ray spectra of silicate mineral materials. This method has been used in the determination of Sc, Cr, Co, Rb. Cs, Eu, Hf and Th in samples of standard rocks and moldavites.     

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.     

Elemental analysis of the marine sediment reference materials MESS-1 and PACS-1 by instrumental neutron activation analysis

Two fairly recent sediment reference materials (MESS-1, PACS-1) have been analyzed by INAA in order to determine the concentration of their elements and to ascertain the homogeneity of each standard. Two rock samples (USGS-GSP-1 and JG-1) were used as standards for the determination of element concentrations, for inter-calibration purposes and also to assess the precision of the technique used. Eighteen elements were determined in these sediments. Comparison of the certified values with our results, where this is possible, indicates the accuracy of the method for environmental studies. These materials were shown to be very homogeneous and hence useful as sediment standards. The data presented here extend the range of useful element concentrations in these reference materials.     

Concentration levels of rare-earth elements and thorium in plants from the Morro do Ferro environment as an indicator for the biological availability of transuranium elements

Plants and soils from a natural thorium and rare-earth element occurrence (Morro do Ferro, Brazil) were analyzed by alpha spectrometry (Th) and ICP-AES (REE), after pre-concentration of the elements by solvent extraction, co-precipitation and ion exchange procedures. Leaching experiments with humic acid solutions and different soils were performed to estimate the fraction of elements biologically available. High concentrations of the light rare-earth elements (LREE) and of Th, reaching some hundreds of g/g-ash, were measured in plant leaves from the areas of the highest concentration of these elements in soil and in near-surface waters. Chondrite normalized REE plots of plant leaves and corresponding soils are very similar, suggesting that there is no significant fractionation between the REE during uptake from the soil solution and incorporation into the leaves. However, Ce-depletion was observed for some plant species, increasing forSolanum ciliatum in the sequence: leaves<fruits<seeds. Soil to plant concentration ratios (CR's) for Th and the REE, based on the total concentration of these elements in soils, are in the range of 10^–3 to 10^–2. Leaching experiments confirmed the importance of humic acid complexation for the bio-uptake of Th and REE and further showed that only a very small fraction of these elements in soil is leachable. The implications of these results on the calculated CR's will be discussed.