Determination of rare earth elements in recent and fossil shells by radiochemical neutron activation analysis

Seven rare earth elements (La, Ce, Sm, Eu, Tb, Yb and Lu) in marine shell samples were determined by neutron activation analysis. In order to measure γ-ray using a Ge(Li) detector without serious interference from the intense Compton background from²⁴Na, a simple radiochemical separation was performed by a co-precipitation method with hydrated iron(III) oxide. The chemical yields for shell samples (91–99%) were determined by a re-activation technique for Gd and Yb. The interference from the²³⁵U(n, fission) reaction was corrected for determination of La and Ce. The data obtained in this study showed the behavior of rare earth elements in shells during the process of fossilization.     

Determination of nanogram levels of lanthanoids in a marine macro-alga by neutron activation analysis combined with separation by selective precipitation

Preseparation of lanthanoids by substoichiometric precipitation of calcium oxalate and simple radiochemical separation of lanthanoids by lanthanum oxalate have been developed. They were combined with neutron activation analysis of a marine macro-alga (Laminaria religiosa, brown alga) sample. Quantitative recovery of lanthanoids throughout the procedure was examined by radiotracer technique. Eleven lanthanoids, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Er, Yb and Lu, at 0.7–140 ng g^–1 were determined with a relative standard deviation of 1–7% (n=3). Concentrations of lanthanoids in the marine macro-alga were compared with land plant and sea water.     

A Revised Periodic Table: With the Lanthanides Repositioned

The lanthanide elements from lanthanum to lutetium inclusive are incorporated into the body of the periodic table. They are subdivided into three sub-groups according to their important oxidation states: La to Sm, Eu to Tm, Yb and Lu, so that Eu and Yb fall directly below Ba; La, Gd, Lu form a column directly below Y; Ce and Tb fall in a vertical line between Zr and Hf. Pm falls below Tc; both are radioactive, and not naturally occurring. The elements with easily attained 2⁺ and 4⁺ oxidation states are grouped and clearly differentiated. Gadolinium has an important position as the centre of four triads in the block of elements that surround it– La, Gd, Lu; Ba, Gd, Hf; Eu, Gd, Tb; Yb, Gd, Ce. This new arrangement has the advantages of compactness, simplicity and clarity – there are no tie lines; and important oxidation states of these metals are emphasized. The actinides are also accommodated within this system, and element 114 falls naturally below lead in Group 14.     

Determination of impurities in titanium and titanium oxide by radiochemical neutron activation analysis

A radiochemical neutron activation analysis has been applied to 2N–4N grade titanium metal and its oxide. Twenty two impurities were separated in a group from scandium by a radiochemical separation method using cation exchange resin with HBr and HCl. The contents of the elements were calculated by a single comparator method using two monitors. The analytical results agree well within 10% deviation with those obtained by instrumental method. Eighteen elements, Na, Fe, Co, As, Se, Sr, Mo, Sb, La, Eu, Tb, Yb, Lu, Hf, Ta, W, Th and U, are determined in titanium oxides and 17 elements, Na, Cr, Fe, Co, Se, As, Zr, Mo, Sb, Cs, Ce, Tb, Yb, Hf, Ta, W and Th, in titanium metals.     

Mathematical Correction for Polyatomic Isobaric Spectral Interferences in Determination of Lanthanides by Inductively Coupled Plasma Mass Spectrometry

The determination of lanthanides by Inductively Coupled Plasma Mass Spectrometry (ICP‐MS) is complicated by several spectral overlaps from M⁺, MO⁺ or MOH⁺ ions formed in the ICP. Especially, it is essential to avoid the spectral interferences from lighter lanthanide and Ba polyatomic ions on middle or heavier lanthanides. To tackle this problem, we have developed a mathematical correction method, which reduces all the spectral overlaps from oxide species of Pr, Nd, Ce and Sm over Gd, Tb, Dy and Ho, and Gd, Tb over Yb and Lu. It can also successfully correct the oxide and hydroxide interference of Ba over Eu. The effectiveness of the proposed the mathematical correction scheme is demonstrated for the USGS Standard Rock samples AGV‐1 and G‐2. The results show that the experimental data obtained by applying the mathematical correction scheme for lanthanides is in good agreement with the reported values, using pneumatic and ultrasonic nebulisation methods, for their ICP‐MS analysis.     

Synthesis,Structures, and Luminescent Properties of Chloride and Nitrate LnIII Complexes Coordinated by tris(Pyrazolyl)methane

We report the synthesis of Ln³⁺ nitrate [Ln(Tpm)(NO₃)₃] ⋅ MeCN (Ln=Yb ( 1Yb ), Eu ( 1Eu )) and chloride [Yb(Tpm)Cl₃] ⋅ 2MeCN ( 2Yb ), [Eu(Tpm)Cl₂(μ-Cl)]₂ ( 2Eu ) complexes coordinated by neutral tripodal tris(3,5-dimethylpyrazolyl)methane (Tpm). The crystal structures of 1Ln and 2Ln were established by single crystal X-ray diffraction, while for 1Yb high resolution experiment was performed. Nitrate complexes 1Ln are isomorphous and both adopt mononuclear structure. Chloride 2Yb is monomeric, while Eu³⁺ analogue 2Eu adopts a binuclear structure due to two μ²-bridging chloride ligands. The typical lanthanide luminescence was observed for europium complexes ( 1Eu and 2Eu ) as well as for terbium and dysprosium analogues ([Ln(Tpm)(NO₃)₃] ⋅ MeCN, Ln=Tb ( 1Tb ), Dy ( 1Dy ); [Ln(Tpm)Cl₃] ⋅ 2MeCN, Ln=Tb ( 2Tb ), Dy ( 2Dy )).     

Precise trace rare earth analysis by radiochemical neutron activation

A rare earth group separation scheme followed by normal Ge(Li), low energy photon detector (LEPD), and Ge(Li)−NaI(Tl) coincidence-noncoincidence spectrometry significantly enhances the detection sensitivity of individual rare earth elements (REE) at or below the ppb level. Based on the selected γ-ray energies, normal Ge(Li) counting is favored for¹⁴⁰La,¹⁷⁰Tb and¹⁶⁹Yb; LEPD is favored for low γ-ray energies of¹⁴⁷Nd,¹⁵³Sm,¹⁶⁶Ho and¹⁶⁹Yb; and noncoincidence counting is favored for¹⁴¹Ce,¹⁴³Ce,¹⁴²Pr,¹⁵³Sm,¹⁷¹Er and¹⁷⁵Yb. The detection of radionuclides^152mEu,¹⁵⁹Gd and¹⁷⁷Lu is equally sensitive by normal Ge(Li) and noncoincidence counting;¹⁵²Eu is equally sensitive by LEPD and normal Ge(Li); and¹⁵³Gd and¹⁷⁰Tm is equally favored by all the counting modes. Overall, noncoincidence counting is favored for most of the REE. Precise measurements of the REE were made in geological and biological standards. Prepared for the U.S. Department of Energy under Contract DE-AC06-76RLO 1830.     

Lanthanide(III) Complexes of 4,10‐Bis(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecane‐1,7‐diacetic acid (trans‐H6do2a2p) in Solution and in the Solid State: Structural Studies Along the Series

Complexes of 4,10‐bis(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecane‐1,7‐diacetic acid (trans‐H₆do2a2p, H₆ L ) with transition metal and lanthanide(III) ions were investigated. The stability constant values of the divalent and trivalent metal‐ion complexes are between the corresponding values of H₄dota and H₈dotp complexes, as a consequence of the ligand basicity. The solid‐state structures of the ligand and of nine lanthanide(III) complexes were determined by X‐ray diffraction. All the complexes are present as twisted‐square‐antiprismatic isomers and their structures can be divided into two series. The first one involves nona‐coordinated complexes of the large lanthanide(III) ions (Ce, Nd, Sm) with a coordinated water molecule. In the series of Sm, Eu, Tb, Dy, Er, Yb, the complexes are octa‐coordinated only by the ligand donor atoms and their coordination cages are more irregular. The formation kinetics and the acid‐assisted dissociation of several Ln^III–H₆ L complexes were investigated at different temperatures and compared with analogous data for complexes of other dota‐like ligands. The [Ce( L )(H₂O)]^3? complex is the most kinetically inert among complexes of the investigated lanthanide(III) ions (Ce, Eu, Gd, Yb). Among mixed phosphonate–acetate dota analogues, kinetic inertness of the cerium(III) complexes is increased with a higher number of phosphonate arms in the ligand, whereas the opposite is true for europium(III) complexes. According to the ¹H NMR spectroscopic pseudo‐contact shifts for the Ce–Eu and Tb–Yb series, the solution structures of the complexes reflect the structures of the [Ce(H L )(H₂O)]^2? and [Yb(H L )]^2? anions, respectively, found in the solid state. However, these solution NMR spectroscopic studies showed that there is no unambiguous relation between ³¹P/¹H lanthanide‐induced shift (LIS) values and coordination of water in the complexes; the values rather express a relative position of the central ions between the N₄ and O₄ planes.     

Determination of rare earths and thorium in apatites by thermal and epithermal neutron-activation analysis

A procedure is described for the non-destructive determination of Na, Mn, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu and Th in apatites by thermal and epithermal neutron-activation of independent portions of the material. The method was applied to three apatites with different contents. The precision obtained was better than +/-5% for La, Ce, Sm, Eu, Gd, Tb and Dy and +/-20% for Yb, Nd, Ho, Er and Lu for an apatite with a total rare-earth oxide content of the order of 1%. Determination of Ce, Tb and Yb could only be carried out with thermal neutron-activation analysis, while Gd, Ho and Er could only be determined after irradiation with epithermal neutrons.     

Determination of trace amounts of gold in the presence of rare earth elements in rock samples from Makhtesh Ramon (Southern Israel), by instrumental epithermal neutron activation analysis

Epithermal neutron activation analysis (ENAA), followed by high resolution gamma-ray spectrometry, was applied to determine trace amounts of Au in the presence of rare earth elements (REE) from vein samples in the basaltic rocks of Makhtesh Ramon, located in southern Israel. The contribution of¹⁵²Eu (411.1 KeV) to the 411.8 keV peak of¹⁹⁸Au was determined using multiple gamma-peak, ratios derived from Eu standards and mixtures of Au and Eu. The concentration of Au was found to be in the range of 10–80 ppb. A group of rare earth elements: La, Eu, Ce, Tb, Sm, Lu, Yb was identified; the concentration of Eu was found to be 0.5 ppm.     

Syntheses, structure and rare earth metal photoluminescence of new and known isostructural A2Mo4Sb2O18 (A=Ce, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) compounds

Nine new A₂Mo₄Sb₂O₁₈ (A=Ce, Pr, Eu, Tb, Ho, Er, Tm, Yb, Lu) compounds have been synthesized by solid-state reactions. They are isostructural with six reported analogues of yttrium and other lanthanides and the monoclinic unit cell parameters of all fifteen of them vary linearly with the size of A³⁺ ion. Single crystal X-ray structures of eight A₂Mo₄Sb₂O₁₈ (A=Ce, Pr, Eu, Gd, Tb, Ho, Er, Tm) compounds have been determined. Neat A₂Mo₄Sb₂O₁₈ (A=Pr, Sm, Eu, Tb, Dy, Ho, Er, Tm) compounds exhibit characteristic rare earth metal photoluminescence.     

Molar enthalpies of formation of LnAl2 compounds

The enthalpy of solution of Eu in Al and the standard molar enthalpy of formation of LnAl₂ (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb) were determined by dissolution calorimetry, using a calorimeter based on liquid aluminium. Experimental results are compared with model predictions.     

Quantum-chemical calculations of the tautomeric forms of azo derivatives of acetylacetone and determination of the stability constants of their complexes with rare-earth metals

The effective atomic charges in the tautomeric forms (enol-azo, keto-azo, and hydrazo) of 3-(2-hydroxy-5-nitro-3-sulfophenylazo)pentane-2,4-dione (L¹), 3-(2-hydroxy-3,5-disulfophenylazo)pentane-2,4-dione (L²), 3-(5-chloro-2-hydroxy-3-sulfophenylazo)pentane-2,4-dione (L³), 3-(2-hydroxy-4-nitrophenylazo)pentane-2,4-dione (L⁴), and 3-(2-hydroxyphenylazo)pentane-2,4-dione (L⁵) were calculated by the Hückel method (MO LCAO). It was found that the hydrazo form is most reactive for meta- and meta’-substituted derivatives (L^1–3) and the keto-azo form is most reactive for para-substituted (L⁴) and unsubstituted ones (L⁵). The stability constants of complexes of rare-earth metals (La, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) with L^1–5 determined by potentiometric titration decrease in the order: Lu > Yb > Tm > Er > Ho > Dy > Tb > Gd > Eu > Sm > Nd > Ce > La. Functionalization of the aromatic part of ligands L affected neither the rare-earth metal: L ratio (1: 2) nor the above order of the stability constants.     

The concentration of rare earth elements in plants and in the adjacent soils

La, Ce, Nd, Sm, Eu, Tb, Yb and Lu were determined in needles of age class 5 from 6 individual Norway spruce trees and in their soils. Measurements were done by neutron activation analysis with a group separation of the REE. Concentrations in spruce needles are among the lowest values reported for plant leaves. Concentrations show small variations between the soils, but large variations between the trees. The mean ratio plant/soil is about 5·10^–3 forall REE except Ce. Needles have no Eu-anomaly and a strong negative Ce-anomaly with respect to the soil. In addition to the fractionation of the individual REE between trees and the soil, there is also a considerable fractionation between the trees.     

Facile Synthesis of Lanthanide (Ce,Eu, Tb,Ce/Tb,Yb/Er,Yb/Ho,and Yb/Tm)‐Doped LnF3 and LnOF Porous Sub‐Microspheres with Multicolor Emissions

Monodisperse YF₃ and YOF porous sub‐microspheres were synthesized by using a novel sacrificing template method with amorphous Y(OH)CO₃ ⋅ x H₂O as the precursors and the template. It was found that the size and shape were well maintained, and the condensed precursor was transformed into uniform porous structures after fluoridation. By fine‐tuning the feed of the fluorine source, the final product could be converted from YF₃ to YOF. A possible growth mechanism is proposed for the uniform porous YF₃ structure and the porous yolk–shell‐like YOF structure. The luminescence properties showed that the as‐synthesized YF₃:Ln³⁺ (Ln=Eu, Tb, Ce, Ce/Tb, Yb/Er, Yb/Ho, and Yb/Tm) products exhibited strong multicolor emissions, which included down‐/upconversion and energy‐transfer processes. Additionally, YOX (X=Cl and Br) could be obtained if a different halogen source was used during calcination. However, the spheres were almost completely destroyed. Our novel synthetic route can also be extended to other lanthanide fluorides (REF₃, RE=Gd, Lu), which may open a facile way to fabricate novel porous nanostructures.     

Determination of rare-earth eleemnts in rock samples by neutron activation analysis

A Ge(Li) detector combined with cation exchange separation has been used for the determination of 12 rare-earth elements (La, Ce, Nd, Sm, Eu, Gd, Tb, Ho, Er, Tm, Yb, and Lu) in rock samples by neutron activation analysis. After purification by the conventional hydroxide-fluoride precipitation, the rare-earth elements are separated into two fractions, light (La-Tb) and heavy (Ho-Lu), by EDTA cation exchange, and the γ-activities of the two fractions are measured by a Ge(Li) detector. The heavy rare-earths, such as Ho, Er, and Tm, can be easily γ-counted without serious interference from the intense Compton background and photopeaks due to the light rare-earths such as¹⁴⁰La,¹⁵³Sm,¹⁵²Eu, and¹⁶⁰Tb. The chemical yields (60%) for the individual rare-earths are determined by a reactivation technique. The results obtained for the U.S. Geological Survey standard rocks G-1 and W-1 are compared with the previously reported data.     

Rare earth elements determination and distribution patterns in sediments of a polluted marine environment by instrumental neutron activation analysis

Results obtained from the analysis of sediment core samples taken froma fairly polluted marine environment were analyzed for the REE contents todetermine the concentrations of La, Ce, Sm, Eu, Tb, Dy and Yb using instrumentalneutron activation analysis. Core samples were divided into strata of between2 to 3 cm intervals and prepared in the powdered form before irradiating themin a neutron flux of about 5.0 . 10¹² n . cm ^—2s ^—1 in a Triga Mark II reactor. Down-core concentration profilesof La, Ce, Sm, Eu, Tb, Dy and Yb in 3 core sediments from three sites areobtained. The shale-normalized REE pattern from each site was examined andlater used to explain the history of sedimentation by natural processes suchas shoreline erosion and weathering products deposited on the seabed and furnishingsome baseline data and/or pollution trend occurring within the study area.The shale-normalized REE patterns also showed that LREE in the sediment samplesexhibit enrichment relative to HREE particularly, La and Sm showing enrichmentcompared to the ratios in shale. REE concentrations of 124 µg/g at thesurface of sediment collected at two of the three sites were found to decreaseto 58 and 95 µg/g, respectively. This was of particular interest whenit is used to explain the anomalies occurring in the marine sediment as aresult of geochemical processes over a long period of time. Changes in concentrationsfrom surface to bottom of the sediments ratioed to Sm concentrations and thecorrelation between concentrations of Sm and these elements were also investigatedand correlation coefficients were calculated for all REEs and sites. Validationof the method used was done using a Soil-7 SRM.     

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.     

Determination of ten lanthanoids in chondritic meteorites by radiochemical neutron activation analysis using coaxial and planar type pure Ge detectors

In order to determine the trace amounts (3 ng–100 ng) of lanthanoids in chondritic meteorites, new and convenient analytical procedures of radiochemical neutron activation method were presented. Applying these procedures to Antarctic meteorites, a total of ten lanthanoids (La, Ce, Nd, Sm, Eu, Gd, Tb, Tm, Yb, and Lu) were precisely determined in a sample of 50–100 mg. Considering several error sources such as counting statistics, collection of interferences, and determination of chemical yield, magnitude of overall error was estimated for each element.     

Determination of rare earth elements in hot spring and crater lake waters by epithermal neutron activation analysis

Determination of the rare earth elements (REE's) in acidic hot spring and crater lake waters by neutron activation analysis (NAA), in which activation was performed mostly by epithermal neutrons (epithermal NAA) was investigated. Nine REE's, La, Ce, Sm, Eu, Tb, Ho, Tm, Yb and Lu, out of fourteen naturally existing REE's were determined at ppb levels with satisfactory precision. The epithermal NAA was found to be more effective in the determination of Sm, Tb, Ho and Yb than normal NAA, in which activation was performed mainly by thermal neutrons. Combined use of the epithermal and normal NAA's enabled the determination of eleven REE's, La, Ce, Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb and Lu.