Determination of actinide nuclides in water samples from the primary circuit of a research reactor

Primary coolant samples from a research have been analyzed for^239,240Pu,²³⁸Pu,²³⁸U,²³⁷Np and²³⁹Np. The determination of²³⁷Np and²³⁸U was carried out with the help of isotope dilution neutron activation analysis with²³⁹Np or²³⁸Np as tracer. For determination of^239,240Pu and²³⁸Pu alpha spectroscopic isotope dilution analysis with²³⁸Pu as tracer was used.²³⁹Np was determined with the help of isotope dilution analysis using²³⁸Np as tracer. Nuclides were isolated by chemical separation on anionite resin. Before measurement, Pu isotopes were electrolytically deposited on stainless steel plates. Activity ratios referred to²³⁸U were reported. They are helpful for identification of the sources of actinide activity in reactor effluents.     

Dosage du237Np en trances dans l'uranium et le plutonium

The²³⁷Np content of²³⁸Pu or²³⁹Pu samples were determined by the gammaspectrometry of²³⁸Np formed by thermal neutron activation. The measurements were carried out on irradiated²³⁸Pu samples directly, and after the chemical separation of²³⁹Pu samples. The²³⁷Np content of natural uranium was determined from the ratio of the alpha-activities of²³⁸Pu and²³⁹Pu isotopes formed from the decay of neptunium isotopes produced by the activation of²³⁷Np and²³⁸U isotopes, respectively.      

Speciation of239U and238Np produced by radiative neutron capture

Various simple and complex compounds of²³⁸U and²³⁷Np have been irradiated in a neutron flux. The chemical state of²³⁹U and²³⁸Np formed in (n, ) reactions has been determined as a function of the initial oxidation state of the actinide elements and of the nature of ligands. A scheme for the chemical reactions following neutron capture is proposed.     

High precision instrumental neutron activation analysis of uranium by multiple gamma-ray peak ratio determination

The method of multiple γ-ray peak ratio determination has been applied to the nondestructive neutron activation analysis of uranium in rocks and ores. The photopeaks of²³⁹Np gamma-rays produced by the activation of²³⁸U and those of the fission products of²³⁵U are a measure of the quantity of uranium in the irradiated sample, provided that the uranium is of natural isotopic composition. The ratios between the integrated areas of the different photopeaks are calculated and compared with those obtained for a uranium standard. The uranium concentration in the sample is calculated from the photopeaks whose ratios correspond, within the error limits to those of pure natural uranium. High accuracy better than ±2% has been obtained.     

The leachability of some natural and man-made radionuclides from soil and sediments on acid attack

A radiotracer study was made of the leachability of some natural and man-made radionuclides from soils and sediments subjected to attack by various acid mixtures. Particular attention was paid to the nuclides²³⁸U,²³²Th, Pa (as²³³Pa) and Np (as²³⁹Np), since for these neutron activation can be used to study recoveries and/or to induce in situ radionuclides in samples. Thus conventional NAA allowed determination of total²³⁸U and²³²Th instrumentally, and also enabled analysis of leachates and residues by radiochemical or instrumental NAA. Activation of these nuclides produced samples endogenously labelled with²³³Pa and²³⁹Np whose behaviour on acid dissolution/leaching could be examined. Furthermore, comparison of neutron irradiated and non-irradiated samples allowed us to investigate the possibility of increased leachability induced by nuclear recoil reactions; however, this effect was negligible. We also investigated the acid leaching of americium adsorbed on the surface of sediment. In general, unsatisfactory leaching recoveries were found for²³³Pa,²³⁹Np and²³²Th for most materials, indicating the need for total dissolution procedures.     

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.     

Simultaneous determination of 226Ra and 238U in soil and environmental materials by gamma-spectrometry in the absence of radium progeny equilibrium

The determination of ²²⁶Ra and ²³⁸U in environmental samples by gamma-spectrometry is most often carried out by hermetic sealing of the sample in a suitable container, waiting until secular equilibrium that has been established in the ²³⁸U decay chain below ²²⁶Ra and counting of the high intensity emissions of ²¹⁴Pb and ²¹⁴Bi. The 186 keV multiplet can then be corrected to provide a measure of ²³⁵U and hence, ²³⁸U. The work presented in this paper involves a critical examination of the analysis of ²³⁸U and ²²⁶Ra in environmental materials without secular equilibrium established between ²¹⁴Pb, ²¹⁴Bi and their progenitor. Results indicate that the correction of the 186 keV doublet via ²³⁴Th determination is possible, even for low-level samples but careful consideration of both experimental conditions and the composition of the sample matrix is required. This revised version was published online in July 2006 with corrections to the Cover Date.     

Non-destructive assay technique for the determination of <Superscript>238</Superscript>U/<Superscript>232</Superscript>Th ratio in the mixed oxides of uranium and thorium using prompt gamma-ray neutron activation

A non-destructive assay technique based on prompt gamma-ray neutron activation analysis for the determination of ²³⁸U to ²³²Th ratio in the mixed oxide fuel materials has been established. The method uses closely spaced high energy gamma-rays in the region of 4000 keV to 4150 keV enabling it to be applied for samples of any geometry and thickness without having any correction for gamma-ray attenuations and detection efficiencies.     

Neutron activation determination of uranium by coprecipitation of neptunium-239 on zirconium phosphate

A method is proposed for neutron activation determination of U via²³⁹Np. This is separated by coprecipitation of ZrO(H₂PO₄)₂ and its 106 keV γ-peak measured. The sensitivity of the determination is 10⁻⁹ g. The method is based on the well-known ability of Np(IV) to coprecipitate with zirconium phosphate, while Np(VI) does not form insoluble phosphates or fluorides. This permits elimination of elements interfering, with the determination of²³⁹Np via the 106 keV γ-peak: Sm, Nd, Yb, Lu, Pa (from Th) and Ta. The rare earths are eliminated by coprecipitation on LaF₃, and Pa and Ta as insoluble phosphates in an oxidizing medium. The method is suitable for phosphorus-containing samples: phosphorites, apatites and their industrial treatment products. The results obtained for the uranium content with the proposed method are in good agreement with the results of other methods and authors.     

Determination of uranium in ores using instrumental neutron activation analysis

An instrumental neutron activation analysis method based on the measurement of²³⁹Np has been developed for the determination of uranium in ores. The samples after 5 sec irradiation were cooled for 3 days and the gamma-ray spectra were measured with a 30 cm³ Ge(Li) detector. The precision and accuracy of the proposed method were determined by analysing IAEA Standard Uranium Ore samples.     

Activation Analysis Methods and Applications

Summary INAA was applied for searching more effective biosorbents for U and Ag among 9 and 47 strains of actinomyces, respectively. Biomasses of strains were tested for the Ag and U sorption capacity from model solution, containing 50 mg/l Ag ions and from technological solution of U-production, containing 7.11 mg/l U ions. The U and Ag samples were irradiated for 5 hours and 20 hours, respectively, at a neutron flux density of 5.3 ^. 10¹³ n ^. cm^-2 ^. s^-1. The Ag content was calculated from the gamma-line of radionuclide ^110mAg (T_1/2 = 250.4d, E_γ= 657.7keV). The U content was calculated from the gamma-lines (228.2 keV, 277.8 keV) of radionuclide ²³⁹Np (T_1/2 = 2.35 d). The error of U and Ag determination (relative standard deviation) was 2-3%.     

Determination of uranium,antimony, indium,bromine and cobalt in atmospheric aerosols using epithermal neutron activation and a low-energy photon detector

Owing to the high ratio of resonance integral to thermal neutron activation cross-section of²³⁸U, a 5 min epithermal neutron irradiation under cadmium shielding, followed by measurement of the 74 keV photopeak of²³⁹U with a high resolution low-energy photon Ge(Li) detector, allows the fast determination of uranium in aerosols collected on a Whatman 41 cellulose filter. Uranium blanks of the cellulose filter paper require correction and limit the sensitivity. Simultaneously the concentrations of the elements cobalt, bromine, antimony and indium can be determined. In Belgium, the uranium concentrations of the aerosols were found to be constant and comparable to the uranium contents of rocks.     

3He induced nuclear reactions on237Np targets

The cross sections for the³He induced nuclear reactions on²³⁷Np leading to the formation of^236sNp,²³⁸Np,²³⁶Pu,²³⁷Pu,²³⁸Pu,²³⁷Am and²³⁹Am were studied by the irradiation of thin and thick targets of²³⁷Np. The cross sections were determined in the energy range of 20–26 MeV using the stacked-foil technique with thin targets. The cross sections were used for the calculation of the thick-target yields for the production of²³⁶Pu,²³⁷Pu and²³⁸Pu from²³⁷Np irradiated with³He²⁺ ions in the energy range of 20–26 MeV.     

Uranium in coral skeletons determined by epithermal neutron activation analysis

A simple and non-destructive method has been proposed for the routine determination of uranium by epithermal neutron activation analysis in coral skeletons. Using a cadmium capsule, about 0.1-0.2 g samples were irradiated for 6 hours in the Triga Mark II Reactor. Measurements of -ray (²³⁹Np via ²³⁹U) were performed with each sample and standard after cooling for about three days. Compared with a non-destructive thermal NAA, the present method was found to improve the sensitivity because it reduced the intense Compton background induced by ²⁴Na. We determined uranium in coral standards within 2% of analytical precision. The data obtained for the carbonate standards are mostly consistent with reported values. The present method could be usefully applied to determine uranium contents in fossil corals from the Funafuti Atoll in the Pacific. The distribution of uranium between seawater and coral skeletons is also discussed in order to understand the environmental media in which the coral grew.     

Measurement of the 238U(n,γ)239U reaction cross sections in the energy range of 2.0–5.0 MeV by using a neutron activation technique

The neutron capture cross-sections of ²³⁸U at the neutron energies of 4.38?±?0.05 MeV, 3.02?±?0.49 MeV and 2.04?±?0.26 MeV have been measured using the activation method and off-line gamma-ray spectrometric technique. The effects of neutron flux fluctuation, multiple scattering, flux self-shielding and gamma-ray self-absorption were corrected. The excitation function of the ²³⁸U(n,γ)²³⁹U reaction was also calculated using the TALYS-1.9 code. The experimental results were compared with the evaluated data, the theoretical data and the previous experimental data.

     

Determination of237Np in spent fuel by use of inherent239Np as a chemical yield monitor

A method for analyzing the content of²³⁷Np in spent fuel has been developed using inherent²³⁹Np as a chemical yield monitor. After ion-exchange separations for the dissolved fuel solution, the²³⁷Np content in the neptunium fraction was determined from the activity of²³⁷Np or of²³³Pa, which is in radioactive equilibrium with²³⁷Np. The chemical yield in the separations was determined both from the content of²⁴³Am which is in radioactive equilibrium with²³⁹Np before the separations and from the²³⁹Np content in the neptunium fraction after the separations by alpha- and gamma-ray spectrometry.     

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.     

The determination of fission products in irradiated uranium by electrophoretic focussing of ions

Electrophoretic focussing of ions was applied to the separation of fission products present in solutions of nuclear uranium fuel irradiated in various European reactors. By combining two separation methods, all the long-lived fission products could be determined individually and quantitatively by counting with a NaI(T1) and a GM detector of known detection efficiency. Radiography and autoradiography were used for semi-quantitative purposes. The concentrations of²³⁵U and²³⁸U were determined from a short post-irradiation of the fuel solution and counting of¹⁴⁰Ba−¹⁴⁰La and²³⁹Np, respectively. An iterative calculus method is presented which allows calculation of the irradiation history of the fuel solution from the above analyses. without any a priori knowledge.     

<Superscript>234</Superscript>U/<Superscript>238</Superscript>U and <Superscript>235</Superscript>U/<Superscript>238</Superscript>U ratios in domestic water from the environs of Obuasi mine in Ghana

Activity concentrations of ²³⁸U, ²³⁵U and ²³⁴U were determined in different sources of drinking water at the Obuasi gold mines and its surrounding areas in Ghana. Water samples collected from the mines and its surrounding areas were analyzed using direct gamma-ray spectrometry and neutron activation analysis. The ²³⁴U/²³⁸U and ²³⁵U/²³⁸U ratios were calculated and the mean values range from 1.27 to 1.38 and from 0.044 to 0.045 respectively. The average ²³⁴U/²³⁸U ratio was from 1.27 for groundwater to 1.38 for treated water, demonstrating the lack of equilibrium. The average ²³⁵U/²³⁸U activity ratio is 0.045, indicating that only natural uranium was detected in the samples investigated.     

Anomalous behaviours of protactinium in the acid-leaching experiments on pitchblende

A series of leaching experiments with H₂O, HCl, HNO₂ and HF were carried out on a sample of pitchblende from Africa. Anomalously high²³¹Pa/²³⁵U ratios, which were not accompanied by similar enhancements of²³⁴U/²³⁸U and²³⁵U/²³⁸U ratios, were observed in some uranium fractions. The observed²³¹Pa/²³⁵U ratios varied between the values of 0.035±0.005 and 2,000±300 (Ci/Ci). These results are interpreted as due, primarily, to the difference in the chemical properties of protactinium and uranium, rather than to the alpha-recoil effects.