Determination of natural uranium in biological samples using the solid state nuclear track detector method

For the solution of most of the problems which are connected to the biological and physiological role of natural uranium in plants and animal organisms about 10⁻¹⁴ g uranium should be determined. However most of the physico-chemical methods for the determination of natural uranium in biomaterials are time-consuming and possess considerable error. On the basis of addition and inner standard methods a version of Solid State Nuclear Track Detectors (SSNTD) method has been developed in order to determine the natural uranium in biospecimens. According to the experimental data simple relations have been obtained for the calculation of uranium concentration in biomaterial and minium uranium concentration in biosolution which can be measured by the detector used. Under irradiation of SSNTD at a thermal neutron flux of (3–5)·10¹⁵n·cm⁻² the detector sensitivity is 2.30·10⁻⁹ g U/ml for glass detectors; 9.60·10⁻¹⁰g U/ml for the detectors made from artificial mica.     

The determination of uranium in biological materials by neutron activation analysis using the fission product134I

A method for the determination of uranium based on²³⁵U thermal neutron fission, has been developed and employed on samples of ashed fish tissue and seaweed. The method involves a post-irradiation ion exchange separation of iodine isotopes. The 884 keV photopeak of¹³⁴I is used for measurement. Uranium detection limits in the samples concerned have been estimated to be 1·10⁻⁸g in terms of natural uranium. The precision achieved in analysing several series of 3–5 samples was 4–10 per cent. The accuracy of the method was tested by employing an independent neutron activation procedure based on²³⁹U measurement. The accuracy of both methods was checked by analysing NBS SRM 1571 ‘Orchard Leaves’.     

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.     

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.     

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.     

A neutron activation analysis procedure for the determination of uranium,thorium and potassium in geologic samples

A neutron activation analysis procedure was developed for the determination of uranium, thorium and potassium in basic and ultrabasic rocks. The three elements are determined in the same 0.5-g sample following a 30-min irradiation in a thermal neutron flux of 2·10¹² n·cm^?2·sec^?1. Following radiochemical separation, the nuclides²³⁹U (T=23.5 m),²³³Th (T=22.2 m) and⁴²K (T=12.36 h) are measured by β-counting. A computer program is used to resolve the decay curves which are complex owing to contamination and the growth of daughter activities. The method was used to determine uranium, throium and potassium in the U. S. Geological Survey standard rocks DTS-1, PCC-1 and BCR-1. For 0.5-g samples the limits of detection for uranium, throium and potassium are 0.7, 1.0 and 10 ppb, respectively.     

Epithermal neutron activation determination of uranium in environmental waters by neptunium-239 after preconcentration on activated carbon

A method for the analysis of uranium in natural waters based on preconcentration of uranium on activated carbon, irradiation with epithermal neutrons, and a high resolution gamma-spectrometry of²³⁹Np was developed. The chemical yield of uranium preconcentration is determined by treating a parallel sample to which a known uranium quantity is added. The lower limit of determination amounts to 1.4·10⁻⁸ g uranium per liter. The possible interfering in gamma-spectrometry of neptunium-239 was discussed too. The applicability of the proposed method is shown by the analysis of uranium in sea-, river-, geothermal-, drinking- and rain-water samples.     

Aktivierungsanalytische Bestimmung von Nickel in Ionenaustauschern

A method for the determination of nickel in ion exchange resins has been elaborated. It is based on the⁵⁸Ni(n, p)⁵⁸Co reaction. Samples of 500 mg are irradiated for 90 h in a fission neutron flux of 10¹³ n·cm⁻²·s⁻¹. After decomposing by HNO₃/HClO₄ mixture the radiochemical separation is carried out by extraction of the Co-DDTC-complex in chloroform. Measuring by a 23 cm³ Ge(Li) detector for 15 h provides a detection limit of 10 ppb. Radiochemical yield is determined by⁵⁷Co as radioactive indicator. Limitations by⁶⁰Co are reduced by Cd-screened activation and by anticoincidence measuring technique.      

Ultra-sensitive determination of K, Th, U and other trace impurities in liquid organic scintillators by NAA

We present a NAA method to determine ultratraces of K, Th, U and other trace impurities in liquid organic scintillators, which are known as ultrapure detector materials for neutrino or dark matter experiments. A combined optimization of relevant factors for sensitive NAA has been realized, leading to a sensitivity for U down to 10⁻¹⁶g/g. Samples of 250 ml have been irradiated up to 120 h at a thermal neutron flux of 5–8·10¹²·n·cm⁻²·s⁻¹. Acidic extraction, wet ashing and TBP-extraction are used for radiochemical separations. Finally, coincidence techniques are applied for increased sensitivity.     

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.     

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.     

Gallium determination in biological samples

A sensitive, simple and time-saving method has been developed for the neutron activation analysis of gallium at concentrations around 10⁻⁴ ppm in biological tissues. After a 24-hour irradiation in a thermal neutron flux of 2.8·10¹³ n·cm⁻²·s⁻¹ and a purification by ion-exchange chromatography to eliminate troublesome elements such as sodium, iron and copper, the⁷²Ga activity is measured with enough accuracy for the method to be applicable in animal physiology and clinical toxicology.     

Study of kinetics,equilibrium and isotope exchange in ion exchange systems. II

The kinetics of isotope exchange in the²³⁸U(VI)-²³³U(VI)-strongly acidic cation exchanger Ostion KS system was studied in the temperature range 275–307K and for total uranium concentration 2.94·10⁻⁴–1.75·10⁻² mol·l⁻¹ in UO₂(NO₃)₂ solution. The experimental results were evaluated by means of the “two-film mass-transfer model” and by the use of Fick's diffusion equations which have been proved more suitable for the system studied than McKay's equation. The influence of the temperature was evaluated using the Arrhenius equation. The diffusion character of the process follows also from the value of the activation energy (15.12 kJ·mol⁻¹). In comparison with the UO ₂ ²⁺ ↔H⁺ ion exchange⁶ the isotope exchange studied is faster and less dependent on temperature (the activation energy is substantially lower).     

Radioactivation analysis of aluminium,vanadium, copper,molybdenum, zinc and uranium in natural water samples using organic coprecipitants

A method is described for the determination of trace metal ions, V, Al, Cu, Mo Zn, and U, in natural water samples by neutron activation analysis, using organic coprecipitation as a preconcentration method. The preconcentration of trace elements was accomplished by converting the dissolved trace metal ions into the oxine chelates atpH 5.2 and extraction of the chelates witho-phenylphenol which is a liquid above 56 °C and solidifies at room temperature. After cooling the extraction system, the fine particles of the organic phase were collected on a millipore filter and the precipitate was air-dried in a clean environment. The solid extract was wrapped up in a sheet of clean polyethylene and subjected to neutron irradiation in a reactor for less than 10 min at a thermal flux of 2·10¹³ n·cm⁻²·sec⁻¹. γ-Ray spectrometry by a coaxial Ge(Li) detector connected to a 1024-channel PHA was performed on the irradiated sample without further chemical separation, and thus the ppb level concentration of the elements in natural water samples could be determined. The fundamental study of the collection of the trace elements is also described.     

Determination of trace impurities in tin by neutron activation analysis

Two methods are described to determine indium and managenese in high-purity tin. In the first method indium and manganese are separated from the tin and antimony matrix activities on Dowex 1X8 anion exchanger. Tin and antimony are adsorbed in 10M HF while indium and manganese are eluted. In the second method the incident γ-ray intensity due to the tin matrix is reduced by placing a lead absorber between the sample and the detector. The reproducibility and the sensitivity of both methods are of the order of 10 ppb for manganese and of 1 ppb for indium for 1 g samples and a neutron flux of 10¹¹ n·cm⁻²·sec⁻¹. Aspirant of the N. F. W. O.     

Neutron activation analysis for ultra low contents of uranium and thorium in aluminium and silica

Highly sensitive neutron activation analysis of uranium and thorium in high quality silica and aluminium has been investigated using the Japan Materials Testing Reactor (JMTR), having a thermal neutron flux higher than 10¹⁴ n/cm²/s. In order to determine ultra-low contents of uranium and thorium,²³⁹Np and²³³Pa as activation products were separated by using anion exchange and LaF₃ coprecipitation methods. As a result, a number of interfering radioactive isotopes containing double neutron capture product such as¹⁸³Ta were removed completely from the isolated²³⁹Np and²³³Pa fraction and the detection limits for uranium and thorium were found to be 2·10^–12 g and 4·10^–13 g, respectively.     

Computer assisted multielement analysis of terrestrial and extraterrestrial materials and studies on long-lived cosmogenic53Mn by neutron activation

In a large number of alpine rocks and respective mineral separates the beryllium distribution was studied via “non-destructive” photon activation. The detection limit of the assembly was ∼20 ppb. The existence of Be-rich areas was revealed. A selection of individual rocks was analysed by instrumental as well as by radiochemical neutron activation analysis for main and trace elements as: Na, K, Sc, Cr, Mn, Fe, Co, Rb, Cs, La, Eu, Yb, Ta, W, Au, and U. The latter was determined by counting the²³⁵U-fission tracks. The data supply an insight into the complex processes leading to the formation of metamorphic rocks. The hardware and the computer evaluation of the γ-spectra is described in some detail. A further application is the determination of traces of⁵³Mn (in the order of 10⁻¹² g/g) produced by the interaction of cosmic rays with stony meteorites. From a comparison of the²⁶Al- and⁵³Mn-values it is concluded that the depth dependent production of these two radionuclides differs slightly.     

Sulfur determination in coal by 14 MeV neutron activation analysis

A procedure involving the irradiation of coal samples with 14 MeV neutrons and subsequent gamma-ray spectrometry of the irradiated sample for the estimation of solfur in coal, has been outlined. The samples were irradiated with 14MeV neutrons from a Cockroft-Walton type generator for one minute and then subjected to gamma-ray spectrometry for another minute using an automated transfer cyclic system. Ten such cycles were repeated for accumulating events under the 2130 keV gamma ray photopeak belonging to³⁴P (T=12.4 s) produced by the³⁴S(n, p)³⁴P reaction for assessing the lower level of detection, LLD, of Sulfur. Interferences due to the presence of other elements in coal were also determined. Sulfur can be determined at LLD of 0.25% in coal provided a 5 g sample of the coal is irradiated with a neutron flux of 5·10⁹ n·cm⁻²·sec⁻¹ assayed with a gamma ray spectrometer having a large hollow core Ge(Li) detector and an anti-Compton shield.     

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 trace impurities in tin by neutron activation analysis

A method was developed for the determination of 15 trace elements in tin. High-purity tin samples (99.9999% and 99.999%) as well as tin of technical quality were analysed. Reactor neutron activation of the tin samples was followed by distillation of the matrix activities from a HBr−H₂SO₄ medium and Ge(Li) gamma-ray spectrometry of the distillation residue. The sensitivity of the method is generally high. For the high-purity samples the detection limits vary from 0.02 ppb (scandium) to 200 ppb (iron) for irradiation of 1 g of tin for 1 week at a thermal flux of 5·10¹²n·cm⁻². ·sec⁻¹. To decontaminate the surface of the tin samples, pre- and post-irradiation etching procedures were applied. The efficiency of these etching techniques was studied.