Precise determination of rare earth elements in rocks by neutron activation analysis

A pre-irradiation group separation method has been developed for the neutron activation analysis of rare earth elements (REE) and Ba in silicate rocks. REE and Ba were quantitatively separated from other elements by cation exchange column method. The chemical yield of each separation was monitored with Pr added to the sample powder before decomposition. The accuracy and precision were tested by repeated analyses of JB-1 and one analysis of BCR-1. In addition, it was found that REE distribution in a granitic rock powder was inhomogeneous and therefore special care must be taken for the sampling of granitic rock powders.     

Neutron activation analysis of bulk samples from Chinese ancient porcelain to provenance research

Neutron activation analysis (NAA) is an important technique to determine the provenance of ancient ceramics. The most common technique used for preparing ancient samples for NAA is to grind them into a powder and then encapsulate them before neutron irradiation. Unfortunately, ceramic materials are typically very hard making it a challenge to grind them into a powder. In this study we utilize bulk porcelain samples cut from ancient shards. The bulk samples are irradiated by neutrons alongside samples that have been conventionally ground into a powder. The NAA for both the bulk samples and powders are compared and shown to provide equivalent information regarding their chemical composition. Also, the multivariate statistical have been employed to the analysis data for check the consistency. The findings suggest that NAA results are less dependent on the state of the porcelain sample, and thus bulk samples cut from shards may be used to effectively determine their provenance.     

Instrumental neutron activation analysis of some rock samples from Akwana and Arufu areas,Middle Benue Trough,Nigeria

Twenty nine (29) major, minor and trace elements including rare earth elements (REEs) were determined by INAA in rock samples from Akwana and Arufu areas, Middle Benue Trough, Nigeria. The rock units are located within the lead-fluorite and baryte mineralisation there. The concentrations of the major elements in the tertiary basalt (TB) and dolerite are similar while the elemental abundance in the granite gnesses is completely different. The elemental concentrations in the rock samples do not show any known relationship with fluorite abundance. The concentrations of some elements in both tertiary basalt and dolerite show them to be derived from alkali basaltic liquid. The chondritic normalised REE distribution patterns for the TB are similar to those of BCR-1 but the chondritic relative REE abundance is more enriched in TB than in the BCR-1. The chondritic normalised REE distribution patterns for the granite gneisses are also compared to those of the standard granite samples.     

Trace element determination in rocks and sediments by neutron activation analysis

Neutron activation analysis (NAA) is one of the most used analytical techniques for trace element determination in rocks, because time consuming operations are avoided. We have analyzed different types of USGS reference materials (G-2, GSP-1, BHVO-1, STM-1, GXR-3, GXR-4, GXR-5), using both thermal (TNAA) and epithermal neutrons (ENAA). ENAA has been used to reduce interferences due to Sc-46 and to other high activities. The following elements have shown an improvement when analyzed by ENAA: Ba, Cs, Gd, Rb, Sb, Sr, Ta, Tb, Th, Tm, U, Yb, Zr; better results were found for Ce, Co, Cr, Eu, Fe, Hf, La, Lu, Na, Nd, Sc, Zn with TNAA. The accuracy of both methods has been tested comparing our results with some published values. The agreement is in general very good. The precision also is satisfactory, being for many elements better than 10%. After these tests, a study on some rock samples from the basaltic plateau of Kenya, east of Gregory Rift, has been performed by ENAA. Among the elements determined in this work, the rare earch elements (REE) can give significant petrogenetic information, by means of their distribution and fractionation in the rocks. The main parameters investigated are the degree of fractionation of light (La to Eu) relative to heavy (Gd to Lu) REE and the occurence of Eu anomalies, when the REE concentrations are compared to chondritic values. The evaluation of detection limits by TNAA has been performed for REE in sediment samples from Thyrrenian Sea (Central Italy).     

INAA determination of holmium in submilligram samples of cosmochemical and geochemical interest and the second-order activation interference

Second-order neutron activation becomes a serious interference in NAA determinations of REE in submilligram samples of meteoritic and terrestrial materials when neutron fluences reach levels of 10²⁰ n·cm^–2 or more. The Dy-interference to Ho determination and the Eu-interference to Gd determination are quite, large. We discuss the importance of second-order activation interferences in REE determinations, and present an experimental method to correct the Dy-interference to Ho determination by INAA. Ho concentrations in splits of less than 0.2 mg of BCR-1 and SP can be accurately determined by INAA with a neutron fluence of 2·10²⁰ n·cm^–2 in spite of large Dy interferences of up to 200%. It is necessary for NAA determinations of REE with high neutron fluences that each REE standard be separated from its neighboring REE, in order to correct the second-order activation interferences experimentally.     

Comparative methods for determination of rare earths in geological and mineral samples

Particle induced X-ray emission (PIXE) has been used for the quantitative analysis of rare earth elements (REE) in thick targets prepared from geological and mineral samples. Measurements were made with 1 and 3 MeV proton beams. For comparison, determination of the same elements was made by X-ray fluorescence (XRF) using a²⁴¹Am annular source. Minimal detectable limits (MDL) have been estimated for the two situations. Neutron activation analysis (NAA) has also been used for the determination of REE at the ppm level.     

ICP-MS multielement determination in fly ash after microwave-assisted digestion of samples

A microwave assisted digestion procedure has been developed for dissolution of fly ash samples prior to the inductively coupled plasma-mass spectrometric determination of their elemental composition. The developed methodology was validated by carrying out the analysis of two high-silicate containing reference materials (CRM 134R sewage amended soil and NIES JR 1 rock) and by means of the comparison between results found by microwave-assisted digestion and ICP-MS of fly ash samples with those found by neutron activation analysis (NAA) for Sb, Cs, Cr, Co, Fe, U and Zn determination. The method developed can be recommended for routine multielement analysis of fly ash.     

Rare earth element patterns in ultramafic rocks of the Schist Belt of Southwestern Nigeria by instrumental neutron activation analysis

24 Ultramafic rock samples from 3 different areas of the Schist Belt of Southwestern Nigeria were analyzed for 11 rare earth elements (REE) by instrumental neutron activation analysis (INAA). REE patterns of the ultramafic rocks are similar for the 3 different areas, and the REE abundances are smaller than for other types of rocks from the same areas. However, the moderate fractionation between LREE and HREE observed for these samples is unusual for ultramafic rocks. Some geochemical implications of the results are discussed.     

Utilization of pneumatic carrier facility of Dhruva reactor for trace element determination by neutron activation analysis

The pneumatic carrier facility (PCF) of Dhruva reactor is being extensively used for neutron activation analysis (NAA) studies pertaining to research work as well as routine sample analysis. It is useful for the determination of trace elements using short and medium half-lives radioisotopes produced in neutron activation with available higher neutron flux (~5 × 10¹³ cm^?1 s^?1). Solid samples placed in high density polypropylene capsule, are irradiated for 1 min duration and radioactive assay is carried out by high resolution gamma ray spectrometry. Design aspects of PCF and various applications to samples of diverse matrices using NAA are presented.     

The non-destructive determination of REE in fossilized bone using synchrotron radiation induced K-line X-ray microfluorescence analysis

The sensitivity and applicability of the synchrotron radiation induced X-ray microfluorescence (μ-SRXRF) spectrometer at the Hamburg synchrotron laboratory Hasylab for the determination of the distribution of trace concentrations of rare-earth elements (REE) in fossilized bone are discussed and critically compared to those of other trace analytical methods such as instrumental neutron activation analysis (INAA) and LAMP-ICPMS (laser ablation microprobe inductively-coupled plasma mass spectrometry). Measurements were carried out on two bone samples from contrasting terrestrial depositional environments at Olduvai Gorge (Tanzania). Results indicate that the microdistribution of the REE in these biological materials is not homogeneous and that the relative abundance of these elements can provide information on the palaeoenvironment during the fossilization process. The heterogeneous distribution of the REE can be determined in a quantitative and completely non-destructive manner provided the concentrations of individual REE are above 10 μg/g.     

Multielemental NAA of geological micro-grain samples for origin identification

Thirty two elements were determined in five pieces of presumed cosmic dust samples with the weights of 5 to 25 g by neutron activation analysis (NAA). All the interferences from fission, threshold reactions and -spectra were corrected for and different counting geometries normalized. Enrichment factors with reference to C1-chondrite are about 200 and 100 for lithophile refractory elements (e.g., V, Th, Hf and W) and rare earth elements (REE), respectively. Deficiencies were observed for Co, Cr, Mg and Na, etc. The C1-chondrite normalized REE patterns are close to those of extraterrestrial materials, with no anomaly of Eu, indicating an extraterrestrial origin of the grain samples analyzed.     

Different methodologies in neutron activation to approach the full analysis of environmental and nutritional samples

Different methodologies of neutron activation analysis (NAA) are now available at the Technological and Nuclear Institute (Sacavém, Portugal), namely Compton suppression, epithermal activation, replicate and cyclic activation, and low energy photon measurement. Prompt gamma activation analysis (PGAA) will be implemented soon. Results by instrumental NAA and PGAA on environmental and nutritional samples are discussed herein, showing that PGAA — carried out at the Institute of Isotope Research (Budapest, Hungary) — brings about an effective input to assessing relevant elements. Sensitivity enhancement in NAA by Compton suppression is also illustrated. Through a judicious combination of methodologies, practically all elements of interest in pollution and nutrition terms can be determined.     

The use of reference materials in the fossil fuels quality control

The determination of trace elements in fossil fuels is of primary importance to achieve correct evaluation of environmental impact of power plants. The characterization of coals and fuel oils can be carried out by several analytical techniques such as ICP-MS, FI-HG-AAS, ETA-AAS, ICP-AES and XRF. The accuracy of the analysis, done to routine basis, can be systematically checked by means of the reference materials available or comparing the results obtained by different techniques. Quality control activities in the field of trace element determination in fossil fuels (coal and fuel oil) are described. The determination of As, Hg and Se in coals was carried out by different techniques (NAA, FI-HG-AAS and FI-ICP-MS) together with the determination of several trace metals in residual fuel oils by NAA, ETA-AAS and ICP-MS. The use of certified reference materials in order to check the accuracy of procedures is discussed and the results obtained for NIST 1632a and NIST 1632b (coal samples) and NIST 1634b and NIST 1619 (fuel oil samples) are reported.     

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.     

Rare earth analysis of usgs rocks SCo-1 and STM-1

Twelve of the rare-earth elements (La, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb and Lu) were determined by radiochemical neutron activation analysis on two samples per bottle from two bottles each of SCo-1 (Cody shale) and STM-1 (nepheline syenite). The data provide no evidence for differences in REE concentrations between bottles of the same rock. Values of the concentrations for most of the REE in SCo-1 and STM-1, based on the samples analyzed, have been established to better than ±10% overall uncertainty, with a 95% confidence limit.     

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.     

Applicability of capillary electrophoresis to the analysis of trace rare earth elements in geological samples.

This study developed a methodology to analyze trace rare earth elements (REEs) in geological materials by capillary electrophoresis (CE). Changed from dilute HNO3 into a water medium by heating, REE ions are detectable at approximately 2 ng mL(-1). In the presence of coexisting elements from geological samples, REE separations were carried out. After sample fusion with Na2O2 and interference separation with ammonium pyrrolidinedithiocarbamate chelate, REE analytes were coprecipitated with Mg(OH)2 at pH 8.5, and then prepared into a water medium for CE determination. Using the standard addition method, this protocol was validated by analyses with better than 5% precision. This method was applied to geological materials; the REE results are in consistence with their certified values. With electrokinetic injection, internal standard (IS) selected among lanthanides is a prerequisite of high-quality REE data. An approach was proposed to derive the IS content for further correcting its contribution from unknown samples.     

Rare earth element (REE) in surface mangrove sediment by instrumental neutron activation analysis

A study is carried out on the concentrations of rare earth element (REE) elements present in surface mangrove sediments from 10 locations throughout west coast Malaysia. In carrying out the analysis, the best and most convenient method being the instrumental neutron activation analysis (INAA). Samples were obtained, dried, crushed to powdery form and samples prepared for INAA. All the samples for analysis were weighted approximately 150 mg for short irradiation and 200 mg for long irradiation time. As calibration and quality control procedures, blank samples, standard reference material SL-1 were then irradiated with thermal neutron flux of 4 × 10¹² cm^?2 s^?1 at the MINT TRIGA Mark II research reactor which operated at 750 kW by using a pneumatic transport facility. The REE elements of surface sediment samples in this study are Dy, Sm, Eu,Yb, Lu, Tb, La and Ce. It was found that the level of concentrations of all the REE elements varies in the range (0.35–117.4 mg/kg). The geochemical behavior of REEs in surface sediments and normalized pattern (chondrite and shale) has been studied. The degree of sediments contaminations were computed using an enrichment factor. The results showed that the enrichment factor varied in the range (0.75–6.75).     

The non-destructive determination of REE in fossilized bone using synchrotron radiation induced K-line X-ray microfluorescence analysis

The sensitivity and applicability of the synchrotron radiation induced X-ray microfluorescence (μ-SRXRF) spectrometer at the Hamburg synchrotron laboratory Hasylab for the determination of the distribution of trace concentrations of rare-earth elements (REE) in fossilized bone are discussed and critically compared to those of other trace analytical methods such as instrumental neutron activation analysis (INAA) and LAMP-ICPMS (laser ablation microprobe inductively-coupled plasma mass spectrometry). Measurements were carried out on two bone samples from contrasting terrestrial depositional environments at Olduvai Gorge (Tanzania). Results indicate that the microdistribution of the REE in these biological materials is not homogeneous and that the relative abundance of these elements can provide information on the palaeoenvironment during the fossilization process. The heterogeneous distribution of the REE can be determined in a quantitative and completely non-destructive manner provided the concentrations of individual REE are above 10 μg/g. Received: 18 January 1998 / Revised: 6 October 1998 / Accepted: 10 October 1998     

Preconcentration of rare earths in geological materials with ascorbic acid for their neutron activation analysis

The potential use of ascorbic acid as a complexing reagent in the separation and preconcentration of rare earth elements (REE) in geological materials in a suitable solid matrix has been demonstrated. Traces of REE from some USGS standard rock samples, viz., GSP-1, G-2, AGV-1 and PCC-1, have been separated after acid dissolution in two ways: (1) by ion exchange chromatography on Dowex 50×8 column and Na-ascorbate as eluent and (2) by direct complexation with ascorbic acid under specific experimental conditions. The separated REE were coprecipitated with the non isotopic diluent, calcium fluoride, before neutron activation analysis. Radiometric determinations showed that the overall recovery of REE in both cases was practically quantitative.