Determination of uranium fission interference factors for INAA

Instrumental neutron activation analysis (INAA) is a very suitable technique for the determination of several elements in different kinds of matrices. However, when the sample contains high uranium concentration this method presents interference problems of uranium fission products. The same radioisotopes used in INAA are formed in uranium fission. Among these radioisotopes are ¹⁴¹Ce, ¹⁴³Ce, ¹⁴⁰La, ⁹⁹Mo, ¹⁴⁷Nd, ¹⁵³Sm and ⁹⁵Zr. The purpose of this study was to evaluate uranium fission interference factors to be used in the INAA of environmental and geological samples containing high levels of U. The obtained interference factors agreed with literature reported values. The results point to the viability of using these experimentally determined interference factors for the correction of uranium fission products.     

Intereferences from uranium fission in neutron-activation analysis in an Argonaut-type Low Flux Reactor

The interferences by uranium fission on the determination by neutron activation analysis of Zr, Mo, Ru, La, Ce, Nd and Sm are investigated for the Argonaut-type Low Flux Reactor at ECN, Petten, The Netherlands. In addition, the spectral interference of the determination of Sm by²³⁹Np is considered. The experimental values for fission yields are found to be in good agreement with calculated values based on recent cross-section compilations.     

Correcting for uranium fission in instrumental neutron activation analysis of high-uranium rocks

Failure to correct for fission products of²³⁵U is shown to result in significant errors in the measured concentrations of La, Sm, Nd, Ba, Zr, and Mo by Instrumental Neutron Activation Analysis of high uranium rocks. Measured and calculated correction factors are presented as the ratio of the fission product to parts per million by weight of uranium in the rock. Potential errors in petrogenetic interpretations of uncorrected data are outlined.     

INAA of Zr,La, Ce and Nd in geological samples in the presence of different uranium concentratios

Rock samples which contain relatively high concentrations of uranium may create problems of interference produced by fission products, when instrumental neutron activation analysis is used. The isotopes⁹⁵Zr,¹⁴⁰La,¹⁴¹Ce, 143Ce and 147Nd, which are commonly used in the neutron activation analysis of the corresponding elements, are also produced as fission products of²³⁵U. For each of these radioisotopes, a contribution factor is calculated theoretically and meaured experimentally using geological samples with different uranium contents.     

Interference in neutron activation analysis of rocks by uranium fission

Interferences by uranium fission for⁹⁵Zr,⁹⁹Mo,¹⁰³Ru,¹⁴⁰La,¹⁴¹Ce and¹⁴⁷Nd have been studied using a single comparator method with two monitors. The effect of the neutron energy spectrum on the interference factor was examined by using the effective activation cross section. All the activities of¹⁴⁰La produced during neutron irradiation of uranium were included in the calculation of the factor for lanthanum. The calculated and experimental interference factors are in good agreement within 10% deviation. The results have been applied for the analysis of several rock samples containing uranium in a wide concentration range.     

Quantitative analysis of trivalent uranium and lanthanides in a molten chloride by absorption spectrophotometry

As an analytical application for pyrochemical reprocessing using molten salts, quantitative analysis of uranium and lanthanides by UV/Vis/NIR absorption spectrophotometry was performed. Electronic absorption spectra of LiCl–KCl eutectic at 773 K including trivalent uranium and eight rare earth elements (Y, La, Ce, Pr, Nd, Sm, Eu, and Gd as fission product elements) were measured in the wavenumber region of 4,500–33,000 cm^?1. The composition of the solutes was simulated for a reductive extraction condition in a pyroreprocessing process for spent nuclear fuels, that is, about 2 wt% U and 0.1–2 wt% rare earth elements. Since U(III) possesses strong absorption bands due to f–d transitions, an optical quartz cell with short light path length of 1 mm was adopted in the analysis. The quantitative analysis of trivalent U, Nd, Pr, and Sm was possible with their f–f transition intensities in the NIR region. The analytical results agree with the prepared concentrations within 2σ experimental uncertainties.     

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.     

Neutron activation analysis of pure uranium: Preconcentration of impurity elements

We have developed a radiochemical neutron activation analysis technique (RNAA) of pure uranium with using extraction chromatographic separation of ²³⁹Np from impurity elements in TBP-6M HNO₃ media. The estimation of influence of fission products of ²³⁵U on the results by radiochemical neutron activation analysis has been carried out. For it we have performed NAA with preconcentration of impurity elements. Experiments show that in this case the apparent concentration of Y, Zr, Mo, Cs, La, Ce, Pr, Nd exceeds the true concentration by 2500–3000 times. Therefore, determination of these elements is not possible by RNAA. This technique allowed to use the determination of 26 impurity elements with detection limit 10⁻⁵–10⁻⁹% by mass. This developed technique may be used for the determination of impurities in uranium and its compounds.     

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.     

Epithermal neutron activation analysis of uranium by neptunium-239 using high resolution gamma-spectrometry

The possibility to use the most intensive gamma-peak of²³⁹Np for INAA of uranium with epithermal neutrons and high resolution Ge(Li)-spectrometry is evaluated. A way for calculation of the peak area of overlapping peaks of¹⁵³Sm and²³⁹Np is proposed. This can be used in other similar cases in the practice of NAA. On this basis a scheme for NAA of uranium in geological objects is proposed. Lower detection limit is 8·10⁻⁸ g U the precision 5–10% (relative standard deviation). The accuracy is demonstrated by the analysis of some geological standard reference materials.     

X-ray fluorescence method for the determination of rare earths, uranium and thorium in allanites

Summary An X-ray fluorescence (XRF) method for the determination of La, Ce, Pr, Nd, Sm, Gd, Th and U in allanites is described. The estimation limits for different impurity elements are La 0.5–10%, Ce 2–20%, Pr 0.1–2.0%, Nd 0.5–10%, Sm 0.1–2%, Gd 0.1–2.0%, Th 0.2–4% and U 0.2–4%. The sample is diluted in the ratio of 19 by boric acid and double layer pellets are prepared. The precision of the method which varies from 0.2–15% has been determined for every element in each standard. Accuracy of the method is assessed by comparison of the values for rare earth, thorium and uranium content with those obtained by optical emission spectroscopic method and the values for uranium and thorium with those obtained by neutron activation analysis.

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Röntgenfluorescenzmethode zur Bestimmung von Seltenen Erden, Uran und Thorium in Allaniten

Zusammenfassung Das beschriebene Verfahren eignet sich zur Bestimmung von La, Ce, Pr, Nd, Sm Gd, Th und U in Allaniten. Die Bestimmungsgrenzen für die einzelnen Elemente betragen: La 0,5–10%; Ce 2–20%; Pr 0,1–2%; Nd 0,5–10%; Sm 0,1–2%; Gd 0,1–2%; Th 0,2–4%; U 0,2–4%. Die Probe wird mit Borsäure im Verhältnis 19 vermischt und zu Doppelschicht-Tabletten gepreßt. Die Reproduzierbarkeit beträgt 0,2–15% und wurde für jedes Element im jeweiligen Standard bestimmt. Die Richtigkeit des Verfahrens wurde durch Vergleich mit Ergebnissen der Emissionsspektralanalyse (SE, U) sowie der Neutronenaktivierungsanalyse (U, Th) beurteilt.

     

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.     

INAA of some phosphates used in fertilizer industries

INAA method for As, Br, Ca, Ce, Co, Cr, Eu, Fe, K, La, Lu, Na, Nd, Sb, Sc, Sm, Tb, Th, U, Yb and Zn determination in raw phosphates and Romanian NPK phosphate fertilizers was applied. The concentration values of uranium and some possible toxic elements in fertilizers are discussed.     

Sequential separation of transuranic elements and fission products from uranium metal ingots in electrolytic reduction process of spent PWR fuels

A sequential separation procedure has been developed for the determination of transuranic elements and fission products in uranium metal ingot samples from an electrolytic reduction process for a metallization of uranium dioxide to uranium metal in a medium of LiCl-Li₂O molten salt at 650 °C. Pu, Np and U were separated using anion-exchange and tri-n-butylphosphate (TBP) extraction chromatography. Cs, Sr, Ba, Ce, Pr, Nd, Sm, Eu, Gd, Zr and Mo were separated in several groups from Am and Cm using TBP and di(2-ethylhexyl)phosphoric acid (HDEHP) extraction chromatography. Effect of Fe, Ni, Cr and Mg, which were corrosion products formed through the process, on the separation of the analytes was investigated in detail. The validity of the separation procedure was evaluated by measuring the recovery of the stable metals and ²³⁹Pu, ²³⁷Np, ²⁴¹Am and ²⁴⁴Cm added to a synthetic uranium metal ingot dissolved solution.     

Feasibility of using dendroanalysis of uranium as a biomarker for environmental contamination

A study was initiated to investigate the chronological deposition of uranium in certain species of trees growing on the site of a former uranium metal processing facility. The Feed Materials Production Center (FMPC) is located in Fernald, Ohio, and for roughly 40 years operated as a large scale uranium processing center. Core samples from several species of trees growing in different locations throughout the site were extracted using a 12.5 mm incremental wood boring drill bit. After extraction, each core sample was cut and packaged into individual sections representing 4 annual growth rings and submitted for instrumental neutron activation analysis (INAA). The reaction ²³⁵U(n,f)¹⁴⁰Ba→¹⁴⁰La+γ was evaluated using high resolution germanium gamma-spectroscopy to detect the 1.596 MeV photon emission from the fission product ¹⁴⁰La following a minimum of a 3 week decay. A total of 106 samples representing 7 individual trees of 3 unique species were irradiated. In addition to the tree-core samples, 18 quality control (QC) samples and 18 standard reference material (SRM) Fly Ash samples were irradiated with the core samples for determining neutron flux. The activity in any one sample in a batch was determined by comparison with the amount of natural uranium in the QC standards. No significantly measurable amount of uranium was detected in any of the tree core samples, although 3 tree core samples were in excess of the minimum detectable amount (30 ng).     

Determination of trace elements in carbonates by instrumental neutron activation analysis

A systematic non-destructive determination of eighteen trace elements (F, Na, Cl, Sc, Mn, Zn, Br, Sr, I, Ba, La, Ce, Sm, Eu, Tb, Yb, Th and U) in carbonate samples by thermal neutron activation analysis was developed. Three 0.2–0.5g samples were irradiated for 15 sec (in the case of determination of F), for 3 min (in the case of Na, Cl, Mn, Sr and I) and for 60 hrs (in the case of Sc, Zn, Br, Ba, La, Ce, Sm, Eu, Tb, Yb, Th and U) in the TRIGA MARK II Reactor at a thermal neutron flux of 5·10¹¹ n·cm⁻²·sec⁻¹ (15 sec and 3 min irradiation) and 1.5·10¹²n·cm⁻²·sec⁻¹ (60 hrs irradiation), respectively. According to the half life of the nuclides formed, the activities were measured with a Ge(Li) spectrometer as follows,²⁰F∶15 sec counting after 20–25 sec cooling,²⁴Na,³⁸Cl,⁵⁶Mn,^87mSr and¹²⁸I∶600 sec couting after 30–120 min cooling,⁸²Br,¹⁴⁰La,¹⁵³Sm,¹⁷⁵Yb and²³⁹Np (daughter of²³⁹U)∶3000 sec counting after 1 week cooling,⁴⁶Sc,⁶⁵Zn,¹³¹Ba,¹⁴¹Ce,¹⁵²Eu,¹⁶⁰Tb and²³³Pa (daughter of²³³Th)∶5000 sec counting after 1 month cooling. The errors due to the fluctuation of the neutron flux and the counting geometry were minimized by the use of calcium determined previously with EDTA-titration as an internal standard. The interferences from²⁴Mg(n, p)²⁴Na and²³⁵U(n, fission) reactions were corrected by the activities produced by the reactions in unit weight of magnesium and uranium, and their concentrations in samples measured experimentally. The data of Na, Mn, Zn and Sr were compared with the results obtained by atomic absorption analysis.     

Chromatographic isolation of144Ce and144Pr from the wastes of irradiated uranium treatment

A two-step chromatographic technique was elaborated to isolate¹⁴⁴Ce,¹⁴⁴Pr from a solution of uranium fission products in 6M HNO₃. The oxidation to Ce(III) by bromate and selective adsorption of¹⁴⁴Ce(IV) on anion exchange column were used to concentrate and purify¹⁴⁴Ce. Some impurities of uranium,⁹⁵Zr,⁹⁵Nb,¹⁰⁶Ru remain in¹⁴⁴Ce solution after the first step of its isolation. The final purification is achieved by passing the 6M HNO₃ solution of¹⁴⁴Ce(IV) through the HDEHP-coated teflon column. The decontamination factors of¹⁴⁴Ce from main fission products are given. 7.2 mCi of (¹⁴⁴Ce+¹⁴⁴Pr) are recovered from each gram of irradiated uranium trioxide with the yield greater than 99%. An improvement of known generator was carried out to elute a purer¹⁴⁴Pr from maternal¹⁴⁴Ce(IV) adsorbed on the anion exchange column.     

Determination of thorium and uranium in activated concrete by inductively coupled plasma mass spectrometry after anion-exchange separation

A sensitive analytical method was established for the determination of Th and U in activated concrete samples. The method combines an anion-exchange separation step with an ICP-MS determination technique. In the ICP-MS measurement, a few μg mL^–1 of Al and Ca, a few ng mL^–1 of Mn, La, Ce, Nd and Pb and pg mL^–1 amounts of Li, Zr, Nb and Ba coexisting in the anion-exchange fraction of Th and U did not interfere. No adverse interference effects were observed in real sample analyses. The obtained detection limits (3σ, n = 10) of Th and U were 2.3 and 1.8 pg mL^–1, respectively. The analytical precisions for ca. 5 μg g^–1 Th and ca. 1 μg g^–1 U in real activated concrete samples were equally less than 7% RSD. The accuracies obtained by the analysis of GSJ rock standard samples were –18.1 to 0.4% for the Th determination and –14.0 to –5.7% for the U determination. The method uses the conventional absolute calibration curve. The internal standard calibration is unnecessary.     

Study of the thermal decomposition kinetics of some rare earth carbonates,fluorocarbonates and fluorooxalates

The thermal transformations of Pr and La carbonates, La, Ce, Pr, Nd, Sm, Eu and Gd fluorocarbonates, and La, Nd, Dy and Ho fluorooxalates were investigated. A Derivatograph Q-1000 (MOM, Hungary) was used for thermal analysis. The kinetics of the processes was studied in a flow reactor. The activation energies and preexponential factors for dehydration and decarbonization were calculated. Samples of Pr fluorocarbonate, Ho fluorooxalate, and Pr and La carbonates were exposed to γ-irradiation (dose from 6.2·10⁶ to 6.1·10⁷ rad). The influence of the irradiation dose upon the kinetic parameters (E _a andA) of the processes was investigated.     

Influence of the postreaction time in the concentration of141Ce anionic species in uranium tricarbonated solutions

An effective method to minimize the presence of¹⁴¹Ce in the final hexahydrated uranyl nitrate recovery product has been obtained. This condition is considered as one prepurification stage in the recovery process of residual nonfissioned uranium in the production of⁹⁹Mo of fission.