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.     

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.     

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.     

Determination of leachable uranium in airborne particulates

The uranium content of airborne particulates collected on cellulose filters was investigated. As a case study, filter samples from the large area of Thessaloniki, Greece, were used. For the uranium determination instrumental neutron activation analysis was used. To obtain equal counting conditions for all samples after irradiation, independent from the initial matrix, uranium was leached from the filter by using a 0.1M NH₄HCO₃ solution, forming a stable uranyl complex [UO₂(CO₃)₃]. This complex was absorbed in a batch process on a small amount of chelating ion exchanger Srafion NMRR, which was directly irradiated in the reactor of the NCSR Demokritos. The study showed that over the investigated time period in 1997 the mean concentration was found to be 0.047 ng U/m³. In relation to the collected amount of airborne particulates having a mean concentration of 0.52 ng/gU. It can be assumed as a natural uranium level in the environment.     

Neutron activation analysis of rare earth impurities in metallic uranium

A method with a sensitivity of 2·10⁻⁷ to 1·10⁻¹⁰% has been developed for determining Yb, Ho, Dy, Gd, Eu, Sm and La impurities in metallic uranium by means of neutron activation. The method is based on a preliminary chromatographic separation of the total amount of rare earth elements from uranium by passing the solution in sulphuric acid through KU-2 cation exchange resin and eluting the traces of uranium retained by the resin with a solution of ascorbic acid. The rare earth impurities are then eluted from the resin with 4–5N HCl, evaporated, and irradiated for 20 hours with a neutron flux of 1.2·10¹³ n·cm⁻²·sec⁻¹. Subsequently the traces of the rare earth elements are co-precipitated with Fe(OH)₃, dissolved in concentrated HCl and separated from the iron and other impurities by passing the solution through Dowex 1X8 anion exchange resin in the chloride form. The individual rare earth elements are then separated from each other using KU-2 cation exchange resin and a solution of ammonium α-hydroxyisobutyrate as the eluant.     

Search for uranium in high purity silicon

Detection of small quantities of uranium in silicon wafers has been carried out by neutron activation followed by observation of fission product¹⁴⁰La. Irradiations of about one week were made at a flux of 6·10¹⁴n cm⁻² s⁻¹ and the activity of the 1596 keV line was determined. Counting rates of as low as 1 count per minute have been observed. This indicates uranium concentrations of about 5·10¹⁰ atoms per cubic centimeter of silicon or about 0.01 mg/g, assuming activity from other fissionable nuclides to be negligible.     

Simplified evaluation of214Bi/238U activity ratios in fossil bones using non-destructive activation analysis

A simple and reliable method has been developed for the evaluation of radioactive disequilibrium state in fossil bones. The fossil bone samples were irradiated with an extremely low neutron fluence, together with a standard pitchblende prevailing the secular equilibrium among the uranium series. The²³⁹Np activity induced from²³⁸U in both samples were adjusted to be gamma-ray spectrometrically nearly equivalent to the naturally occurring radioactivities by controlling the neutron flux and cooling time. Using single gamma-ray spectrometry of the irradiated samples, the determination of²¹⁴Bi/²³⁸U in a fossil bone was carried out by comparing the photopeak ratios of²¹⁴Bi /609 keV/ and²³⁹Np /278 keV/ instead of²³⁸U with the same ratios from the pitchblende standard sample.     

Determination of trace concentrations of thorium in uranium oxide matrix by epithermal instrumental neutron activation analysis

An epithermal instrumental neutron activation analysis (EINAA) method using cadmium filter was standardized to determine trace concentrations of thorium in four samples of uranium oxide (U₃O₈) samples. Samples and thorium standards, wrapped with cadmium foil, were irradiated at a reactor neutron flux of about 10¹² cm^?2 s^?1. Radioactive assay was carried out using a Compton suppressed anticoincidence gamma ray spectrometer consisting of HPGe-BGO detectors coupled to MCA. Concentrations of thorium in these samples were found to be in the range of 15–72 mg kg^?1. EINAA results were validated by determining thorium concentrations in uranium matrix by standard addition method. EINAA results were compared with those obtained by two wet chemical methods namely ion chromatography (IC) and inductively coupled plasma atomic emission spectrometry (ICP-AES). The results obtained by the three methods were found to be in good agreement, indicating further validity of the proposed EINAA method.     

Elemental analysis in bed sediment samples of Karnafuli estuarine zone in the Bay of Bengal by instrumental neutron activation analysis

The concentration of rare earths and other elements have been determined in the bed sediment samples of Karnafuli estuarine zone in the Bay of Bengal by instrumental neutron activation analysis (INAA). The samples and the standards soil-5, soil-7, coal fly ash and pond sediment were prepared and simultaneously irradiated for short and long time at the TRIGA Mark-II research reactor facility of Atomic Energy Research Establishment, Savar, Dhaka. The maximum themal neutron flux was of the order of 10¹³ n·cm^–2·s^–1. After irradiation the radioactivity of the product nuclides was measured by using a high resolution high purity germanium detector system. Analysis of -ray spectra and quantitative analysis of the elemental concentration were done via the software GANAAS, it has been possible to determine the concentration level of 27 elements including the rare earths La, Ce, Sm, Eu, Tb, Dy and Yb and uranium and thorium.     

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.     

Analysis of phosphate rock samples for vanadium using accelerator-based thermal neutrons

Extensive sedimentary phosphate deposits exist in the Sirhan-Turayf basin in northwestern Saudi Arabia containing significant amounts of uranium, thorium, vanadium and rare earth elements. The determination of the concentration and pattern of distribution of some of these elements is essential for economic aspects. This study reports the analysis of vanadium in selected phosphate rock samples from the basin using accelerator-based thermal neutrons activation analysis (TNAA). Samples were irradiated in a thermal neutron flux of 2.5·10⁶ n·cm⁻²·s⁻¹. The induced activity was measured with a HP-GMX detector coupled to a PC-based data acquisition and analysis system. The facility was calibrated using certified standards of vanadium. The minimum detection limit of vanadium was about 1 mg. Three independent measurements on each sample yielded comparable results indicating the reliability of the technique. The vanadium concentrations in the samples vary from 23 to 457 ppm. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

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.     

Non-destructive determination of nuclear fuel burn-up by measuring the gamma radiation of fission products in irradiated uranium oxide

The burn-up of²³⁵U was determined in two uranium oxide samples (0.713 and 89.9%²³⁵U in mixture) irradiated simultaneously with a cobalt monitor, from the amounts of⁹⁵Zr,¹⁰³Ru,¹³⁷Cs,¹⁴⁰Ba and¹⁴⁴Ce obtained by measuring the intensities of the corresponding gamma radiations. The samples were irradiated for 23 days, and the fission products were measured after cooling for 100 days, nondestructively, by means of a Ge(Li) spectrometer. The integrated neutron flux was determined by measuring the produced⁶⁰Co in the cobalt monitor. The burn-up in both samples was determined by measuring the intensity of eight gamma energies (0.5–1.6 MeV). The determined values are in good agreement. The standard deviation of the mean value ( ) is 5%. The atom per cent fission of²³⁵U in both samples, calculated according to , differs by 1%. The measured σ _f for²³⁵U is in good agreement with the data reported in the literature.     

Production of a <Superscript>173</Superscript>Lu target for neutron capture cross section measurements

Lutetium has been used as a radiochemistry detector to measure neutron fluence in NTS tests. A measure of the neutron capture cross sections on ¹⁷³Lu is needed to improve the interpretation value of the Lu radiochemistry isotopic ratios. A natural hafnium target was irradiated with protons to produce neutron poor lutetium radioisotopes. The short lived species were allowed to decay prior to chemical processing resulting in predominantly ¹⁷³Lu with a small amount of ¹⁷⁴Lu. This material was deposited on a titanium foil for use in the neutron capture cross section measurement.     

Multi-element determination in sandstone rock by instrumental neutron activation analysis

Summary Instrumental neutron activation analysis (INAA) was used for the qualitative and quantitative analysis of sandstone samples of Aswan area, in South Egypt. The samples were properly prepared together with standards and simultaneously irradiated by a neutron flux of 7 ^. 10¹¹ n ^. cm^-2.s^-1. in the TRIGA research reactor facilities in Mainz. The gamma-spectra from a hyperpure germanium HPGe detector were analyzed. The present study provides the basic data of elemental concentrations of a sandstone rock. The following elements have been determined: Na, K, Fe, Sc, Cr, Co, Zr, Ce, La, Nd, Sm, Eu, Yb, Lu, Hf, Ta, Th and U. Energy dispersive X-ray fluorescence (EDXRF) was used for comparison and to detect elements which can be detected only by this method.     

Radiochemische Untersuchungen zur Verteilung von129J und3H in Bestrahltem Kernbrennstoff aus Leistungsreaktoren

The working techniques used for the investigation of¹²⁹I and³H sectional distribution in highly irradiated UO₂ pellets are described. The analytical samples are taken by a micro drilling technique. For the determination of¹²⁹I concentration in the UO₂ samples neutron activation analysis following iodine separation from uranium and bulk fission products is used.³H is measured by liquid scintillation counting after distillation. Reliability of the analytical results is discussed as well as possible interferences.     

Multi-element determination in silicate rocks by instrumental neutron activation analysis

Instrumental neutron activation analysis technique was applied for the determination of 20 elements in 54 silicate rock samples which belong to three sedimentary geological formations located in the western desert of Iraq. The samples along with USGS standards were irradiated in an IRT-5000 reactor at a neutron flux of 3.7·10¹³ n·cm^–2·s^–1 The following minor and trace element constituents have been determined: Na, K, Ca, Fe, Sc, Cr, Co, Zr, Ce, La, Nd, Sm, Eu, Tb, Yb, Lu, Hf, Ta, Th and U.     

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.