Determination of isotopic composition of lithium by neutron activation analysis; comparison with mass spectrometry

An activation analysis method is described for routine determination of⁶Li-abundances in various lithium compounds on the basis of the reaction sequence⁶Li(n,α)T and¹⁶O(t, n)¹⁸F and the measurement of¹⁸F. Irradiations of diluted equeous solutions of samples containing CrO₃ as internal flux monitor were carried out at a thermal neutron flux density of ϕ≤10¹¹ n·cm⁻²·sec⁻¹. Interferences from variations in neutron self-shielding oxygen concentration and triton range do not exceed 0.5% when using the dilution technique. The results for⁶Li abundances from 3.52 to 7.60% with standard deviations of 1 to 2.5% were confirmed by mass spectrometric measurements.     

Determination of lithium isotopic composition by thermal ionization mass spectrometry in seawater

The isotopic composition of lithium in seawater has been determined by thermal ionization mass spectrometry (TIMS) based on the use of lithium hydroxide as the ion source. Isotopic measurements in a reference material supplied by IAEA (L-SVEC Li₂CO₃) were made to check the reproducibility of the method and ⁶Li indicates mobilization of light isotope of lithium form the sediment.     

Determination of lithium by instrumental neutron activation analysis

The fast transfer system in the DR 2 reactor for irradiation at a thermal neutron flux density of 10¹³ n·cm⁻²·sec⁻¹ was used for the determination of lithium by the⁷Li(n, γ)⁸Li reaction. β-counting with a large perspex Cerenkov detector begun at 0.3 s after the end of irradiation, and multi-scaler data was accumulated in 300 channels at 0.1 s per channel. With a suitable choice of discrimination level only¹⁶N and background interfere, and the 0.84 s half-life of⁸Li was resolved by the method of weighted least squares. Results are presented for 36 international geochemical reference materials, and for a few biological samples, including BOWEN's kale and the NBS Standard Reference Material 1571 Orchard Leaves.     

Determination of lithium in graphite by neutron activation analysis

Trace impurities of lithium in graphite is one of the sources of tritium in high-temperature reactors. To determine contents of less then 1ng/g a procedure based on the (n,)-reaction of⁶Li was developed. The samples are irradiated in a reactor and then ignited in a Wickbold apparatus. Thereby the tritium produced by the (n,)-reaction is completely converted in HTO, which can be easily purified by distillation and, if necessary, by a scavenger precipitation step. Several types of graphite have been investigated and the lowest content measured was 0.2 ng/g.     

Plutonium isotopic composition measurement by high resolution gamma-spectrometry

Plutonium isotopic composition and the activities of non-separate transuranic elements:²³⁷Np and²⁴¹Am, are determined in the presence of long lived-fission products traces, by gamma-spectrometric measurements with a Ge-ultrapure detector. The quantitative values from the gamma-spectra analysis, are presented comparatively to mass-spectrometric data. This work has been done under AIEA, UNPD 7455/Rom. program.     

Determination of isotopic thorium in biological samples by combined alpha-spectrometry and neutron activation analysis

The determination of isotopic thorium by alpha-spectrometric methods is a routine practice for bioassay and environmental measurement programs. Alpha-spectrometry has excellent detection limits (by mass) for all isotopes of thorium except²³²Th due to its extremely long half-life. This paper reports a pre-concentration neutron activation analysis (PCNAA) method for²³²Th that may be performed following alpha-spectrometry if a suitable source preparation material is utilized. Human tissues and other samples were spiked with²²⁹Th and the thorium was isolated from the sample using ion exchange chromatography. The thorium was then electrodeposited from a sulfate-based medium onto a vanadium planchet, counted by alpha-spectrometry, and then analyzed for²³²Th by neutron activation analysis. The radiochemical yield was determined from the alpha-spectrometric method. Detection limits for²³²Th by this PCNAA method are approximately 50 times lower than achieved by alphaspectrometry.     

Determination of isotopic composition of boron

Investigations were carried out on the determination of isotopic composition of boron using Cs₂BO ₂ ⁺ ion and thermal ionisation mass spectrometry. The results show distinct advantage over the normally used Na₂BO ₂ ⁺ ion.     

The elemental and isotopic determination of lithium by the coincidence measurement of complementary particles

The coincident measurement of both nuclear products at their complementary angles was used to determine⁶Li by the reactions⁶Li(d, α)⁴He and⁶Li(p, α)³He, and⁷Li by the reaction⁷Li(p, α)⁴He. Elemental lithium was determined in natural samples or samples of known isotopic composition. Isotopic analyses could be carried out over the entire range from 0 to 100 atom% with a relative standard deviation of about 4%. The CMCP technique is highly specific and effectively eliminates interference and background.     

Simultaneous determination of boron and lithium by activation analysis

Simultaneous determination of boron and lithium is done by double irradiation with protons. One irradiation with 1.55 MeV protons and another with 7.4 MeV protons, measuring in both cases the amount of⁷Be formed /⁷Li/p,n/⁷Be and¹⁰B/p,/⁷Be/. Deuteron bombardment was not found to be of much advantage.     

Determination of isotopic ratios of osmium and ruthenium in meteorites by pretreatment and radiochemical neutron activation analysis

The isotopic abundance ratios of¹⁹⁰Os/¹⁸⁴Os and⁹⁶Ru/¹⁰²Ru for the metal phases of the Jilin and Taonan stone meteorites were determined by pretreatment and radiochemical neutron activation analysis. All experimental factors affecting Os and Ru isotopic ratios were discussed, including sampling, standard, irradiation, separation and counting. The statistical errors of measurement for the¹⁹⁹Os/¹⁸⁴Os ratio can be controlled within 1%. The experimental results indicate that the statistically significant anomalies of the¹⁹⁰Os/¹⁸⁴Os and⁹⁶Ru/¹⁰²Ru ratios have not been found relative to the terrestrial Os and Ru standards.     

Determination of 17 trace elements in gallium arsenide by reactor neutron activation analysis

A method has been developed for the simultaneous determination of 17 trace elements in gallium arsenide. The method involves reactor neutron irradiation of the samples, distillation of the arsenic matrix activity and Ge(Li) γ-ray spectrometry. For a sample size of 0.1 g and a 10-day irradiation at 2·10¹³ n cm^-2 s^-1, the detection limits vary from 70 p.p.b. (tin) down to 5·10^-3 p.p.b. (scandium).     

Determination of the elemental composition of copper and bronze objects by neutron activation analysis

A method for the elemental analysis of copper and bronze objects is described. Na, Co, Ni, Cu, Zn, As, Ag, Sn, Sb, W, Ir and Au are determined through instrumental neutron activation analysis. Mg, Al, V, Ti and Mn are determined after chemical separation using anionic exhange. The detection limits for a number of other elements are also given. Results for NBS standard reference materials are presented and the results compared with the recommended values. The agreement is good. The results of the analysis of five ancient bronze and two copper objects are presented.     

Determination of traces of lithium in biological, environmental and metal samples by neutron activation analysis

Summary Lithium in environmental, biological and metal samples was determined by neutron activation analysis via the⁶Li(n,)T and¹⁶O(T,n)¹⁸F reactions. The samples were converted to aqueous solutions either by dissolution or by digestion and their aliquots were irradiated in a nuclear reactor for 2 h. The irradiated sample solution, was placed in a ZrO₂ column on which the¹⁸F nuclide was adsorbed. Most of the coexisting nuclides²⁴Na,⁸²Br,³⁸Cl,⁶⁴Cu, etc. were separated by elution with pH 1 3 solution. The column was subjected to a Ge(Li) detector for-ray spectrometry. The lithium content in the sample was estimated from the¹⁸F activity obtained. The matrix effect can be eliminated by either strong dilution of the samples in aqueous medium or by the method of standard addition. Lithium can be determined with high precision and accuracy in sub-ppm samples.

---

Bestimmung von Lithiumspuren in biologischen, Umwelt- und Metallproben mit Hilfe der Neutronenaktivierungsanalyse

Zusammenfassung Lithium wird über die Reaktionen⁶Li(n,)T und¹⁶O(T,n)¹⁸F bestimmt. Die Proben werden durch Auflösung oder Aufschluß in wäßrige Lösung übergeführt und im Reaktor 2 h lang bestrahlt. Die bestrahlte Lösung wird auf eine ZrO₂-Säule gegeben, wo die¹⁸F-Nuklide adsorbiert werden. Die meisten anderen Nuklide (²⁴Na,⁸²Br,³⁸Cl,⁶⁴Cu usw.) werden durch Elution mit Säurelösung pH 1 3 abgetrennt. Die-Spektrometrie erfolgt mit einem Ge(Li)-Detektor. Der Lithiumgehalt ergibt sich aus der¹⁸F-Aktivität. Durch starke Verdünnung oder durch das Standardzugabeverfahren kann der Matrixeffekt eliminiert werden. Lithium ist so mit hoher Präzision und Genauigkeit in sub-ppm-Proben bestimmbar.

     

Neutron activation analysis of6Li isotopic abundance using a low background liquid scintillation counter

A neutron activation method based on the measurement of tritium radioactivity produced by⁶Li (n,)³H reaction was applied to determine the isotopic abundance of⁶Li in aqueous solution with known lithium concentration. Tritium radioactivity was measured with a low background liquid scintillation counter over a period of 2000 min. The present method demonstrated a good linearity between the isotopic abundance of⁶Li and tritium radioactivity produced per unit amount of lithium in a wide range of lithium concentration. A comparison of the present data with those from mass spectrometry showed agreement, though our method was 10 times less sensitive, than mass spectrometry. The present new approach should thus prove quite useful for determining the isotopic abundance of⁶Li.     

Accurate measurement of neodymium isotopic composition using Neptune MC-ICP-MS

This paper reports the measurement of the Neodymium isotopic composition by Neptune Multiple Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS) over the last two years. Although there is concomitant Cerium in the chemical separation process, this has no significant influence on the Neodymium analysis. As for the sample containing small amounts of Samarium (Sm/Nd < 0.04), direct calibration for isobaric interference and mass discrimination by the exponential law can be obtained by assuming that Samarium mass discrimination is the same as that of Neodymium. Geological samples after traditional chemical separation were measured by Neptune MC-ICP-MS and Thermal Ionization Mass Spectrometry (TIMS) respectively. The results show that Neptune MC-ICP-MS can measure Neodymium isotopic composition as precisely the TIMS does and is even more effective and less time-consuming than the TIMS Method. __________ Translated from Chinese Journal of Analytical Chemistry, 2007, 35(1): 71–74 [译自: 分析化学]     

Atomicm absorption spectrometric determination of the isotopic composition of lithium by an ultimate absorbance-ratio technique

The conventional absorbance-ratio technique for determining the isotopic composition of lithium by atomic absorption spectrometry is improved by the use of “ultimate absorbance ratios” of sample solutions. These ratios are obtained by extrapolating the linear portion of lithium content/absorbance-ratio plots to the intercept at 0 mol m^?3 lithium. These graphs are obtained measuring the absorbances of solutions of known ⁶Li abundance and of various lithium contents with natural and ⁶Li-enriched lithium hollow-cathode lamps. Linear calibration is attained over the range 0.0–99.3% ⁶Li, and the lithium isotopic abundance can be determined with an absolute error of ±0.7% ⁶Li for > 0.01 mol m^?3 lithium solutions. The method requires neither prior measurement of the total lithium content in sample solutions nor adjustment of the content to match that in the standard solutions.     

Trace characterisation of lithium niobate by neutron activation analysis

Summary Coprecipitation behaviour of As, Au, Co, Cr, Cu, Eu, Fe, Ir, La, Lu, Mn, Mo, Nb, Ni, Pd, Pt, Sb, Sc, Ta, W, Zn and Zr during precipitation of hydrous oxide of niobium from lithium niobate was investigated. The matrix was dissolved in HF-HNO₃, evaporated to dryness and niobium was precipitated from HNO₃-H₂O₂ medium. The recovery studies were made using radiotracers. A radiochemical separation scheme based on group precipitation has been developed for the determination of Au, Co, Cr, Cu, Fe, Mn, Ni, Pd, Pt, Zn, Zr and rare earth elements. The method was applied to the analysis of lithium niobate. This analysis has provided fruitful information for improving the quality of the crystal.     

Determination of activable isotopic tracers of zinc by neutron activation analysis for study of bioavailability of zinc

A procedure of pre-irradiation concentration of zinc in fecal samples using anion exchanger was developed for the study of the bioavailability of zinc by neutron activation analysis. The mass ratios between⁷⁰Zn and⁶⁸Zn, or⁶⁴Zn and their contents between natural zinc and enriched zinc are used to calculate the bioavailability of zinc when the abundance of the isotope⁷⁰Zn is not high ehough.     

Variable isotopic composition of lead as a source of systematic error in proton activation analysis

This paper considers the variable isotopic composition of lead as a possible source of systematic errors in proton activation analysis. The importance of this source of error was evaluated for environmental and geological samples. As proton activation analysis is frequently used for the certification of lead, the error was determined for three sediment reference materials. Inductively coupled plasma-mass spectrometry was used for the determination of the isotopic composition of lead. The systematic error amounted for the sediments to approximately 1%.     

Simultaneous determination of nitrogen and lithium by thermal neutron activation analysis

The determination of lithium and nitrogen in a variety of materials by thermal neutron activation is described. The nuclear reactions used are ¹⁴N(n,p)¹⁴C and ⁶ Li(n,α)³H. Radionuclides. ¹⁴C and ³H for counting are isolated by fusion of the irradiated sample in a vacuum system. Data are presented on lithium and nitrogen concentrations in several terrestrial standards. The new method allows reliable measurements on 10–50-mg samples.