Rapid determination of fluorine in coral skeletons by non-destructive neutron activation analysis using 20F

A rapid non-destructive technique has been proposed for the determination of fluorine in coral skeletons by thermal neutron activation analysis, using the short half-life ²⁰F nuclide (11.0 s). About 0.2-0.5 g samples were irradiated for 10 seconds in a Triga Mark II Reactor. Soon after the irradiation (25-35 s), measurements of -rays were performed with each sample and standard. The method has the drawback of low sensitivity (20 ppm of F), and the manual operation employed in the cooling step could lead to less precise measurements. We determined fluorine in coral standards within ~8% of analytical precision. The result obtained for the dolomite standard was fairly consistent with literature values, but those for the limestone standard showed to be considerably higher than the reported values. The present method was applied for the determination of fluorine in modern corals from Khang Khao Island, Thailand and Okinawa, Japan. Two core samples of an ancient reef from Funafuti Atoll were measured for fluorine to compare with modern samples. In order to understand the environmental media in which coral grew, the partition of fluorine between seawater and coral skeletons is also discussed.     

Non-destructive determination of uranium and thorium in geological materials by resonance-neutron activation analysis

A simple method is described for the determination of uranium and thorium in gological materials. The samples are irradiated in a reactor with resonance and fast neutrons behind a cadmium filter. Compared with an irradiation with the whole reactor neutron spectrum, the matrix activities are reduced to about 1%, those of uranium (²³⁹Np) and thorium (²³³Pa) to about only 50 and 25%, respectively. This relative diminution of matrix activities allows the γ-measurement of²³⁹Np and²³³Pa as early as after two days' cooling time; in samples with high uranium contents the determination of²³³Pa requires one month's cooling time. This non-destructive procedure yields a detection limit of 0.1 ppm for uranium and thorium in samples of 200 mg, with an error of ±5%. Dedicated to ProfessorW. Borchert on the occasion of his 60th birthday.     

Application of gamma-ray spectrometry for the assay of uranium in crude UF4—An input material used for producing nuclear grade U-metal at the natural uranium conversion plants

A -spectrometric method has been developed for the assay of uranium in crude UF₄, which is used as a secondary source of input material for producing nuclear grade U-metal at natural uranium conversion plants. The method makes use of a NaI (Tl) detector coupled with a multichannel analyzer. The 1 MeV -ray of²³⁸U is used for calibration. A method for the fabrication of uniform -assay calibration standards is also suggested, based on the results of this investigation. The calibration standards were prepared by soaking the matrix in uranium solution and then drying the whole material. The amount of²³⁸U in the crude UF₄ sample was directly estimated by comparing the areas under the 1 MeV -ray peak of known calibration standards with the corresponding areas of the samples to be measured. 100 g each of the standard and the sample were counted. 5 crude UF₄ samples were analyzed by this method. The uranium contents in these samples were found to be in the range of 12.2–28.7 g. To compare the -ray spectrometry results with a completely independent method, chemical analysis by potentiometry of all the samples was also done. The -spectrometric results were found to agree within ±18% with the chemical analysis results.     

Determination of uranium and plutonium in shielding concrete

The formation of plutonium radionuclides (^239+240Pu) from uranium was determined in dismounted shielding concrete from accelerator components. Plutonium and uranium fractions were separated by radioanalytical techniques and measured by -spectroscopy. The measurements are consistent with yield calculations based on transport and single particle codes. The yield of ^239+240Pu did not exceed the two-fold exemption limit given in the Swiss Radiation Protection Law, thus the plutonium content in shielding concrete should not cause problem for the environment.This revised version was published online in November 2005 with corrections to the Cover Date.     

Determination of trace amounts of uranium in silicate materials by means of neutron activation analysis involving rapid radiochemical separation

We determined uranium in silicate materials such as standard rocks and a meteorite by radiochemical neutron activation analysis. After activation with a cadmium cover, samples were subjected to radiochemical separation of uranium immediately. The gamma-ray intensity of²³⁹U was measured with a planar type pure germanium detector system. Our data are mostly consistent with the literature or reported values. Compared with a non-destructive method, the present method was found to improve the sensitivity by at least a factor of ten. Several errors which might be involved in our RNAA procedures were examined and their degrees were evaluated.     

Simultaneous determination of trace uranium and thorium by radiochemical neutron activation analysis

A method for the simultaneous, radiochemical neutron activation analysis of uranium and thorium at trace levels in biological materials is described, based on a technique known as LICSIR, in which a double neutron irradiation is employed. In the first, long irradiation²³³Pa (27.0 d) is induced by neutron capture on²³²Th and then the sample is cooled for several weeks. A second short irradiation to induce²³⁹U (23.5 m) is followed by a rapid sequential radiochemical separation by solvent extraction of²³⁹U with TBP and²³³Pa with TOPO. Chemical yields of²³⁹U and²³³Pa were measured for each sample aliquot using added²³⁵U and²³¹Pa tracers from the -spectra of the separated fractions. The technique was validated by quality control analyses.     

Simultaneous determination of hafnium and zirconium in low grade uranium ores using INAA

A non-destructive neutron activation analysis technique has been developed for the determination of hafnium and zirconium in low grade uranium ores. In order to calculate the fission contribution of²³⁵U, thermal neutron absorption cross-section /_a/ for⁹⁴Zr has been determined. The study shows that 1 g of uranium produces the same activity as from 10.03 g of zirconium. Based on this fact, the degree of interferences have been calculated for each sample and the necessary corrections have been applied. The values have been compared with the reported IAEA and NBS values.     

A new application of neutron activation analysis with239U to determine uranium in groundwaters

A rapid neutron activation method was developed to determine very low levels of uranium (gl^–1) in groundwater from the Palmyrides region, Central Syria. The²³⁹U -ray at 74.7 keV energy was used in the measurements. Results of this technique were compared against the conventional neutron activation analysis (INAA) with²³⁹Np and the laser-induced fluoremetry (LIF). In general, the three data sets showed a very good agreement. The described method provides good accuracy, precision and low detection limit, particularly when the total dissolved solids (TDS) of the samples is low.     

Speciation of239Np in neutron irradiated uranium compounds

The chemical state of²³⁹Np formed in the -decay of²³⁹U produced by thermal neutron capture in²³⁹U, has been determined in simple uranium compounds as well as in macrocyclic complexes of this element. It is shown that the behavior of neptunium depends on such factors as the nature of the target, the counter-ion of the complex, the dissolution medium and the pH. The change of the oxidation state of²³⁹Np with time and the effect of the presence of macroscopic amounts of²³⁸UO ₂ ²⁺ and of²³⁸U(IV) in the solution have also been investigated. The results are discussed in terms of the hot atom behavior of²³⁹U and of the genuine effects of -decay.     

Alpha-recoil atoms of plutonium in the environment

The -recoil effect of²³⁹Pu has been observed in environmental samples and theN ₅ ^P /N₅ ratio in these samples has been calculated. This ratio in atmospheric samples is in the range between 10^–5 and 10^–4 (atom/atom). For other contemporary terrestrial samples it is in the range between 10^–7 and 10^–6 (atom/atom), while that of uranium mineral is about 10^–10 (atom/atom). The results further explain the radioactive fallout contamination of our environment by uranium and plutonium isotopes.     

Die Bestimmung von Uran und Plutonium im Rahmen der Ausscheidungsanalyse

Zusammenfassung Eine in der Praxis angewandte Analysenmethode zur Bestimmung von Plutonium in Harnproben wurde mit Hilfe von Tracerversuchen mit²³⁶Pu,²³³U und²⁴¹Am hinsichtlich ihrer radiochemischen Ausbeute und ihrer Trenneffizienz überprüft. Dabei zeigte sich, daß die Pu-Bestimmung mit einer Ausbeute von 95% praktisch quantitativ erfolgt. Im allgemeinen ist es nicht notwendig, vom Restgehalt an Uran, der 25% beträgt, weiter abzutrennen. Bei Uranmengen bis zu 100g U (nat.) sind die Meßproben alphaspektrometrisch zur qualitativen und zur quantitativen Auswertung geeignet. Auf diese Weise kann neben der Pu-Bestimmung aus demselben Alphaspektrum einer Harnprobe auch eine Aussage über die Isotopenzusammensetzung des Urangehaltes und eine mengenmäßige Abschätzung getroffen werden.Die Abtrennung des²⁴¹Am erfolgt dagegen vollständig. Der Restgehalt an²⁴¹Am in der durch Elektrodeposition hergestellten Pu-Meßprobe wurde mit weniger als 0,3% ermittelt und ermöglicht eine Auswertung des Alphaspektrums auch auf²³⁸Pu.Die Ergebnisse von Routinemessungen im Rahmen der Personenüberwachung zeigten einen normalen Urangehalt im Harn von <0,3g U/l und einen normalen Plutoniumgehalt von 0,05 pCi²³⁹Pu/24 h-Harn.

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The determination of uranium and flutonium in excretion analysis

Summary A routine method for the determination of Pu in urine samples was tested with tracer amounts of²³⁶Pu,²³³U and²⁴¹Am for its recovery and for efficiency of radiochemical separation. Pu recovery was 95%, uranium about 25%, which in generally does not need to be separated for-spectrometric determination of Pu. With uranium content up to 100g U_(nat.) counting sources are suitable for qualitative and quantitative evaluation of-spectra. In this way additionally information about the isotopic composition and the amount of uranium in the urine sample can be achieved from the same measurement.Separation from²⁴¹Am, however, can be assumed quantitatively. The activity of²⁴¹Am in such counting sources prepared by electrodeposition was less than 0,3% which enables evaluation of²³⁸Pu too. Results of routine determinations in personnel monitoring show normal background levels of uranium concentration in urine samples of less than 0,3g U (nat.)/l and for plutonium of 0,05 pCi²³⁹Pu/24-hr urine samples.

     

High precision elemental abundances for tektites and crater glasses-thorium,uranium and potassium

Thorium, uranium and potassium mean abundances for 15 Ivory Coast tektites, 23 Australites, 10 Philippinites, 25 Thailandites, 16 Bediasites and 12 Moldavites are reported. Abundances are also reported for Muong Nong type tektites, Nordlinger Ries crater glass, Bosumtwi crater glass and Darwin crater glass. Previous measurements are reviewed. The value of the present work lies in the fact that high precision instrumental neutron activation analysis was employed to measure a large number of tektites encompassing the major strewn fields. Four independent measurements of thorium were made for each specimen with two Ge(Li) gamma spectrometers. Two of the measurements were based on the 312 keV gamma of²³³Pa, while the other two measurements were based on the uranium and X-rays which accompany the decay of²³³Pa. Internal consistency among the four thorium measurements is high. The uranium measurements were based on the 106 keV gamma of²³⁹Np, while potassium was measured from the 1524 keV gamma of⁴²K.     

Determination of environmental actinide nuclides and210Pb(210Po) by low-energy photon spectrometry with alpha-spectrometry

Low-energy photon spectrometry with -spectrometry was used to determine the environmental concentrations of low-level actinides and other nuclides, especially²¹⁰Pb and²¹⁰Po. The isotopic ratio of²⁴⁰Pu/²³⁹Pu was successfully determined by measuring L_x-ray/-ray counting ratio. A reliable method has been developed for the determination of extremely low-level²³⁷Np global fallout in environmental samples. The non-destructive determination by Ge-LEPS for natural²¹⁰Pb in various samples (tobacco leaves, commercially available tobacco, etc.) was also carried out with the determination of²¹⁰Po by -spectrometry using²⁰⁹Po as a yield tracer.     

A combined method of neutron activation analysis and radiometric measurements for <Superscript>234</Superscript>U and <Superscript>238</Superscript>U determination in soil samples of low uranium concentration

A method that combines the use of non-destructive neutron activation analysis and high-resolution α spectrometry has been developed for determination of the activities of ²³⁴U and ²³⁸U in geological samples of low uranium content. The ²³⁸U content is determined by k₀-based neutron activation analysis, whereas the ²³⁴U/²³⁸U relationship is measured by α spectrometry after isolation and electrodeposition of the uranium extracted from a lixiviation with 6 M HCl. The main advantage of the method is the simplicity of the chemical operations, including the fact that the steps destined to assure similar chemical state for the tracer and the uranium species present in the sample are not necessary. The method was applied to soil samples from sites of the North Peru Coast. Uranium concentration range 3–40 mg/kg and the isotopic composition correspond to natural uranium, with about 10% uncertainty.     

Isotopic analysis of uranium by neutron activation and high resolution gamma ray spectrometry

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.     

Actinides in the near release from the Chernobyl NPP accident

Actinide elements concentrations in the products of near release from CNPP accident were estimated. The data on uranium,²³⁷Np,²⁴¹Am and plutonium and curium isotopes content in fuel particles are given. Sums of -emitting radionuclides and plutonium isotopes in reactor graphite particles and of uranium,²⁴²Cm,^239+240Pu isotopes in the soil and aerosol samples were also determined. By 1989 soil and dust contamination in near release of the accident is due to long-lived -emitting plutonium isotopes.     

Non-destructive determination of low-level210Pb and226Ra with an ordinary high-purity Ge-detector

A convenient non-destructive method for the determination of low level²¹⁰Pb and²²⁶Ra with an ordinary high-purity Ge-detector is presented. The ordinary Ge-detectors used in this work were available to measure 46.5 keV -rays of²¹⁰Pb. These detectors were also useful for the non-destructive analysis of low-level²²⁶Ra in lime-stone and calcium chemicals when a stream of nitrogen gas was maintained around the detectors. By this method, measurements could be carried out not only for²¹⁰Pb and²²⁶Ra but also for other -emitting radionuclides simultaneously, using the same detector. The detection limits of about 1 Bq per sample for²¹⁰Pb and about 0.05 Bq per sample for²²⁶Ra, respectively, were estimated, when the samples were counted for 1–2 days.     

Influence of daughter radionuclides on Purex-process parameters

Experimental and calculated data are presented which concern the limiting influence of²³⁹Np,²³⁷U,²³³Pa,²³⁴Th,²²⁸Th (with daughter radionuclides) on the final decontamination of uranium, plutonium and neptunium from -emitters in Purex-process for NPP fuel reprocessing. It was found, in particular, that in the investigated flowsheet²²⁸Th follows neptunium(IV) and²³³Pa accompanies plutonium. The influence of accumulated daughter -emitters on ionization characteristics of end products in storage up to 100 years was studied. It is shown that stored regenerated uranium and plutonium may require repeated reprocessing just before refabrication.     

Determination of fluorine in coral skeletons by instrumental neutron activation analysis

Summary A systematic and non-destructive technique is proposed for the determination of fluorine in coral samples by instrumental neutron activation analysis using the ¹⁹F(n,γ)²⁰F reaction. About 50 to 80-mg samples in polypropylene capsules were irradiated for 15 seconds in the pneumatic transfer tube system (PN-3) of JRR-3M reactor. After the irradiation at a thermal neutron flux of 1.5 ^. 10¹³ n ^. cm^{-2 .} s^-1, the coral samples and standards were cooled for 6 seconds and the g-rays emitted were measured for 15 seconds with a Ge detector. The sequence from sample irradiation to g-ray counting was performed under a computer-control mode. The analytical precision was ~5% for the JCp-1 coral standard. The present method was applied to the determination of fluorine in corals from Thailand, Okinawa and the Philippines. The advantage of one method over destructive techniques is discussed by comparing the analytical results obtained for the JCp-1 coral standard using INAA, ion chromatography and spectrophotometry. Factors that may control the levels of fluorine in corals are also discussed.