Authors:R. Cretella, R. Lukaszew, J. Dal Fávero, and R. Servant
A technique for isotopic submicrosample analysis of uranium by TIMS is presented. The heating pattern, used was modified in order to improve the precision for microsample analysis of SRM U-500 /NBS/ The technique was applied to submicrosample isotopic analysis of SRM U-150 /NBS/ and found satisfactory.
The coincident measurement of both nuclear reaction products at their complementary angles was used for the isotopic analysis
of boron by the reactions10B(d,p)11B and11B(d,α)9Be. Both isotopes were determined simultaneously with a relative standard deviation of ±2.5%.
Isotopic analysis of243Cm and244Cm has been tried by using a newly developed internal conversion electron spectrometer with high energy resolution. As a result, it was demonstrated that the above isotopes can be determined individually, accurately and precisely, and that the isotopic ratio is also possible to determined sensitively by measuring only the ratio of gross counting rate of internal conversion electrons to that of alpha-rays.
A sequential radiochemical procedure for isotopic analysis of uranium and thorium in soil has been developed. Analysis involves total dissolution of the samples to allow equilibration of the natural isotopes with added tracers, followed by radiochemical separation using anion exchange chromatography (BioRad AG 1–X8). Further separation and purification is performed employing solvent extraction techniques. Finally, the U and Th fractions are co-precipitated with lanthanum and cerium fluoride, respectively, and quantified by alpha-particle spectrometry. Overall chemical yields range from 60 to 90%. Under normal operating conditions and present counting set up, the minimum detectable concentration (MDC) is approximately 2 Bq/kg for soil samples. This is based on one gram aliquot of sample, 80% chemical yield, and 1000 minute counting with a detector having about 15% counting efficiency. The procedure has been successfully tested with Standard Reference Materials. Various soil samples were analyzed with high chemical yields and fine quality of alpha-spectra. Decontamination factor studies were performed to determine the extent of the carry over of210Po,225Ac,226Ra, and229Th into U fraction and210Po,225Ac,226Ra, and232U into Th fraction.
Thermal ionization mass spectrometry (TIMS) is an effective method for isotopic and ultra-sensitivity determination of plutonium.
This project aims at improving the National Institute of Standards and Technology (NIST) TIMS system sensitivity for the analysis
of plutonium from environmental samples. The TIMS detection limits for direct, electrodeposition, and resin bead source loading
techniques were determined by systematically varying the amount of plutonium loaded on the rhenium filament. It has been shown
in our preliminary work that the resin bead could produce a stable TIMS ion beam for as long as 6 h period with »108 Pu atoms loaded onto a single resin bead.
A methodology for the isotopic determination of lithium in enriched7LiOH.2H2O samples by SSMS is described. The photoplate emulsion calibration curve was not used. The accuracy of the results was checked against the analysis of LiOH.2H2O with natural isotopic composition, and it was found that the result obtained was accurate within 5% with respect to the published natural value. The accuracy was improved using an enriched in7Li reference sample. The technique was applied to the analysis of batches of7LiOH.2H2O to be used in a nuclear power reactor to control the pH in the water cooling system.
Authors:R. Michel, U. Herpers, H. Kulus, and W. Herr
On applique l'activation neutronique aux mesures d'abondance isotopique du rhénium dans les matériaux lunaires. On y parvient
en comparant les activités induites par (n, γ) de186Re et188Re au moyen des raies γ de respectivement 137 et 155 keV. Afin d'éviter les interférences, (spécialement celles de199Au et99mTc) on a besoin d'un procédé conduisant à une grande pureté radiochimique. De plus, on détermine les teneurs en rhénium et
tungstène. On a remarqué une anomalie isotopique du rhénium dans les échantillons d'Apollo-14, montrant un enrichissement
remarquable en187Re (de 1,4 à 1,8% dans les sols et jusqu'à 29% dans les brèches). On montre enfin que cet enrichissement est partiellement
dû à l'irradiation neutronique sur la surface lunaire par la réaction186W(n,γ)187W
187Re. Cependant, l'anomalie observée, causée principalement par les neutrons intermédiaires, n'est pas produite uniquement par
les neutrons lunaires. L'activation d'un réacteur y contribue aussi par la réaction:186W(n,γ)187W
187Re(n,γ)188Re, qui peut être corrigée par l'analyse d'étalons de tungstène irradiés simultanément. On estime que la contribution lunaire
à l'enrichissement du187Re est de 20 à 60% de l'excès total observé.
A method is described for the non-destructive and accurate determination of the isotopic composition of uranium by activation
analysis. The high resolving power of Ge(Li) detectors permits easy identification on a single gamma spectrum of the gamma
peaks of239Np formed from238U by activation and those of fission products formed from235U. The ratio of the peak intensities is proportional to the238U/235U ratio in the sample. A precision of ±0.6% has been obtained.
Charged particle spectrometry was used to determine the isotopic concentration of lithium in lithium fluoride targets irradiated
with a deuteron beam of 4.0 MeV. Alpha particles emitted by the6Li(d, α)4He and7Li(d, α)5He reactions were used as a measure of6Li and7Li, respectively. From the6Li/7Li α-count ratio the isotopic concentration of6Li was determined for isotopic concentrations over the range 7.42 (natural) to about 30 atom%6Li, with a relative standard deviation of±4.1%. Alpha particles from the19F(d, α)17O reaction could also be measured as an internal standard, extending the measurements from natural to 100 atom%6Li and giving a relative standard deviation of ±1.9%. The effect of target thickness on the accuracy of the determinations
Authors:I. Kuleff, R. Djingova, A. Alexandrova, V. Vakova, and B. Amov
Lead stocks of wooden-lead anchors found along the Bulgarian Black Sea coast and typologically dated VI c. B.C.-III c. A. D. have been analyzed for chemical composition and lead isotope ratios by INAA, AAS and mass spectrometry. Using multivariate methods for analysis as well as simple bivariate plots the lead for production of the stocks was localized as originating from Laurion, Thassos, Troas, Chalkidike and the Rhodopes. In general, the chemical composition is not recommended to be used for provenance study of lead artefacts. Combining the results from this study with the existing typological classification certain conclusions about the production and distribution of lead anchors in the Aegean region are made.