Determination of rare earths in rare-earth concentrates by neutron activation analysis

Neutron activation analysis was applied to the determination of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Yb, Lu and Th in rare-earth concentrates resulting from minerals. High-resolution gamma-ray spectrometry with a Ge(Li) detector was used for the non-destructive determination, and a single comparator method using Co as flux monitor was applied.     

Determination of rare earths in geological samples by neutron activation analysis

The significance of rare earth distribution patterns in trace element geochemistry is briefly reviewed. Established methods for their determination at the Reactor Centre by instrumental and radiochemical techniques are described, and examples of recent applications discussed.     

Determination of traces of rare earths in high-purity thorium dioxide by neutron activation analysis

The use of thorium dioxide as a nuclear fuel requires the determination of individual rare earth impurities at 0.08–1 mg kg^?1 levels. Neutron activation is sufficiently sensitive but separation from the matrix is essential. In the proposed method, thorium dioxide (5–20 g) is dissolved in concentrated nitric acid with a little hydrofluoric acid; after evaporation, thorium is complexed with ammonium carbonate and the solution is passed through a small column of Chelex-100 resin which retains the rare earths quantitatively without retaining thorium. The rare earth elements are eluted with dilute nitric acid, concentrated, and irradiated with standards; after irradiation the rare earth are collected on a lanthanum carrier and measured by γ-ray spectrometry. The recoveries of rare earths were checked with tracers and by standard addition to thorium dioxide matrices. The reproducibility for La, Eu and Dy was satisfactory at 0.01, 0.003 and 0.002 mg kg^?1, respectively; as was the reproducibility for all rare earths added to thorium dioxide (1–4 μg/5 g). Limits of detection are adequate for certification of nuclear-grade material.     

Neutron activation analysis of heavy rare earths

A method of nondestructive activation analysis of heavy rare earth elements (Sm−Lu) is described. Intensities of γ-ray peaks are compared to that of an internal reference after irradiations by both thermal and fission spectrum neutrons. Results are obtained from computer comparisons of peak areas. Work was performed at the Ames Laboratory of the U.S. Atomic Energy Commission. Contribution No. 2895.     

Determination of rare earths by high-resolution X-ray spectrometry following neutron activation

Reactor neutron activation followed by high-resolution X-ray spectrometry has been applied to the non-destructive quantitative determination of the rare earth elements in naturally occurring materials. The various sources of error as well as the possibilities of minimizing them are discussed.     

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.     

Determination of rare earths in low grade uranium ores and SRM-rock by instrumental neutron activation analysis

An instrumental neutron activation analysis technique has been developed for simultaneous determination of 10 REE in low grade U/Zr ores and other geological materials. The samples were irradiated with reactor neutrons for 2 min to 8 hrs followed by a cooling of 30 min to 3 weeks. The γ-ray activity was measured with a semi-planar Ge(Li) detector. A precision of 5% has been obtained by the repeated analysis of NBS-SRM. The technique is relatively simple and adaptable on the routine basis.     

Analysis of low levels of rare earths by radiochemical neutron activation analysis

A procedure for the radiochemical neutron-activation analysis for the rare earth elements (REE) involves the separation of the REE as a group by rapid ion-exchange methods and determination of yields by reactivation or by energy dispersive X-ray fluorescence (EDXRF) spectrometry. The U. S. Geological Survey (USGS) standard rocks, BCR-1 and AGV-1, were analyzed to determine the precision and accuracy of the method. We found that the precision was ±5–10% on the basis of replicate analysis and that, in general the accuracy was within ±5% of accepted values for most REE. Data for USGS standard rocks BIR-1 (Icelandic basalt) and DNC-1 (North Carolina diabase) are also presented.     

Spectrophotometric determination of the rare earths yttrium and cerium by bromopyrogallol red

A method is described for the spectrophotometric determination of microgram quantities of rare carths, yttrium and cerous cerium ions, using the colour of the complexes formed with bromopyrogallol red. The procedure has been applied to pure solutions containing 10–50 μg of the element.     

Determination of carbon in copper by photon activation analysis

Determination of carbon in copper has been studied by photon activation analysis using 30 MeV bremsstrahlung. Chemical separation of carbon as CO₂ was performed by the combustion method in a high flow rate of oxygen stream. It has been demonstrated that the trace amount of carbon in copper can be determined accurately and precisely, and that the detection limit is 0.02 g.     

Interference by neutron induced second order nuclear reaction in activation analysis of rare earths

In determining the trace impurities existing in high-purity rare earth samples by the neutron activation analysis, there are much interference due to nuclides induced from neutron induced second order nuclear reaction. This paper presents the degree of interference calculated over the ranges of irradiation time from 10⁵ to 10⁷ sec and of thermal-neutron flux from 1·10¹² to 1·10¹⁵ n·cm⁻²·sec⁻¹. According to the results of these calculations, degree of interference under the neutron irradiation condition for 288 hrs in the thermal-neutron flux of 3·10¹³n·cm⁻²·sec⁻¹ is concluded to be 6.4·10⁶ ppm Gd in Eu, 2.2·10⁴ ppm Sm in Eu, 1.9·10⁴ ppm Ho in Dy, 1.1·10³ ppm Eu in Sm, 1.1·10² ppm Ce in La and 1.1·10 ppm Tb in Gd, respectively. Especially, the Gd determination in the Eu target is extremely affected by¹⁵³Gd formed from the¹⁵¹Eu (n, γ) reaction. On the contrary, this reaction is effective in producing¹⁵³Gd activity.     

Determination of fluorine in standard rocks by photon activation analysis

A highly sensitive determination of fluorine in standard rocks by photon activation using the¹⁹F(,n)¹⁸F reaction combined with pyrohydrolysis for the separation of¹⁸F has been reported. The irradiation energy was operated at 20 MeV to avoid the interference from Na, because Na is one of the major element in rocks and¹⁸F is also produced from Na via²³Na(,n)¹⁸F reaction above its threshold energy, 20.9 MeV. After irradiation, fluorine was extracted by pyrohydrolysis and separated as LaF₃ precipitate. It was ascertained that the average recovery of fluorine in standard rocks was about 90% and the precipitate was of high radiochemical purity. This method was applied to the analysis of ten GSJ rock reference samples and two USGS standard rocks issued by the Geological Survey of Japan and the United States Geological Survey, respectively. The detection limit of this method was 0.02 g/g, and the results obtained by this method were in good agreement with the recommended values. This method was easily applied to the determination of a few ppm level of fluorine in rock samples, such as ultrabasic rock and feldspar.     

Determination of rare earths in silicate rocks by epithermal neutron activation and a simple group separation

The determination of nine rare earth elements in rock samples by epithermal neutron activation, followed by a simple group-separation procedure and Ge(Li) γ-ray spectrometry, is described. This method is found to be advantageous for the determination of Nd, Gd, Ho, Er and Lu by means of the short-lived nuclides¹⁴⁹Nd,¹⁵⁹Gd,¹⁶⁶Ho,¹⁷¹Er and^176m Lu. Precision for La, Sm and Eu is similar to that of thermal neutron activation, that for Dy is worse. Samples of the standard rocks, basalt BCR-1 and granite G-2, were analyzed by this procedure and the results obtained are compared with previously reported data.     

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 nitrogen in boron carbide by instrumental photon activation analysis

Boron carbide is widely used as industrial material, because of its extreme hardness, and as a neutron absorber. As part of a round-robin exercise leading to certification of a new reference material (ERM-ED102) which was demanded by the industry we analysed nitrogen in boron carbide by inert gas fusion analysis (GFA) and instrumental photon activation analysis (IPAA) using the ¹⁴N(γ,n)¹³N nuclear reaction. The latter approach is the only non-destructive method among all the methods applied. By using photons with energy below the threshold of the ¹²C(γ,n)¹¹C reaction, we hindered activation of matrix and other impurities. A recently installed beam with a very low lateral activating flux gradient enabled us to homogeneously activate sample masses of approximately 1 g. Taking extra precautions, i.e. self-absorption correction and deconvolution of the complex decay curves, we calculated a nitrogen concentration of 2260 ± 100 μg g⁻¹, which is in good agreement with our GFA value of 2303 ± 64 μg g⁻¹. The values are the second and third highest of a rather atypical (non-S-shape) distribution of data of 14 round-robin participants. It is of utmost importance for the certification process that our IPAA value is the only one not produced by inert gas fusion analysis and, therefore, the only one which is not affected by a possible incomplete release of nitrogen from high-melting boron carbide. Figure Twin-Detector system for analyzing spatially extended samples     

Prompt analysis of rare earths by high-energy PIXE

Thin targets of rare earth fluorides were bombarded with 66 and 85 MeV protons. Measured cross sections for X-ray production agreed with PWBA calculations. Satellite X-rays from nuclear reactions were obtained for both (Z-1) and (Z+1) products from the bombardment of element Z. Interference-free sensitivities were of the order of tens of nanograms under bombardment with 1 mC of integrated charge. The technique was applied for the analysis of geological ores and standards.     

Activation analysis of rare earths : The determination of rare earths in minerals by the single comparator technique

The determination of rare earths in minerals by activation analysis is described. The rare earths are separated as a group from the bulk of the material before irradiation. After irradiation the rare earths are separated from each other by gradient elution with ammonium α-hydroxyisobutyrate on a cation-exchange column. The elements are determined by the single comparator technique. This method permits a practical application of activation analysis to the routine determination of rare earths in complex matrices,