An evaluation of the delayed neutron counting method for simultaneous analysis of uranium and thorium and for235U/238U isotopic ratio determination

This paper describes an evaluation of activation analysis by delayed neutron counting to determine uranium and thorium simultaneously in geological materials and to measure²³⁵U/²³⁸U isotopic ratios. A procedure to isolate the thorium before the irradiation was studied and adapted for use when the interference of uranium makes the nondestructive thorium analysis impossible.²³⁵U/²³⁸U ratios were determined in standards with²³⁵U abundances from about 0.5 to 93%, in milligram size samples. Discussion on precision, accuracy and total error of the method is presented.From a thesis submitted by M. J. A. ARMELIN to the University of São Paulo in partial fulfillment of the requirements for a Doctor of Science Degree in Nuclear Technology.     

Optimum timing parameters in 14 MeV neutron activation analysis of thorium and uranium using delayed neutron counting

A detailed theoretical treatment of cyclic activation analysis of thorium and uranium using a 14 MeV neutron generator and delayed neutron counting is presented. Variations of the detector response with sample transfer and total experiment times are examined in order to obtain the optimum cycle periods for the maximum detector response. Cycle optimization for 95% and 90% of the maximum detector response is investigated. Furthermore, elimination of the delayed neutrons produced by the reaction¹⁷O(n,p)¹⁷N is also considered in optimum cycle timing. Finally, calculations are carried out to estimate detection limits for thorium and uranium. Experimental results will be reported in a subsequent paper.     

Uranium and thorium analyses by delayed fission neutron counting technique using a small neutron generator

Applicability of a small neutron generator and a dual rectangular tube sample transfer system for analyses of U and Th using delayed fission neutron technique has been investigated. A way of optimizing the timing parameters is reported. At a fast neutron flux of 10⁸ n.cm^–2s^–1, 0.02 w% U can be determined. For thorium determination this method is less sensitive. The Cd difference technique can be used for the simultaneous determination of U and Th but it has lower sensitivity.This work was supported in part by the IAEA.     

A titrimetric method for the sequential determination of thorium and uranium

A method for the sequential determination of thorium and uranium has been developed. In the sample solution containing thorium and uranium, thorium is first determined by complexometric titration with ethylenediaminetetraacetic acid (EDTA) and then in the same solution uranium is determined by redox titration employing potentiometry. As EDTA interferes in uranium determination giving positive bias, it is destroyed by fuming with HClO₄ prior to the determination of uranium. A precision and accuracy of better than ±0.15% is obtained for thorium at 10mg level and uranium ranging from 5 mg to 20 mg in the aliquot.     

An automatic uranium analyser based on delayed neutron counting

An automated device for the analysis of uranium is described. The analyser comprises a sample transfer system, a neutron counter, a microprocessor and a teletype. A set of 100 samples, 14 ml of maximum volume, is analysed without manual intervention. The capacity is 45 samples per hour. Using a 10 g sample the detection limit is 0.06 ppm and uranium concentrations of 1 ppm can be determined with a precision of better than ±5%. The only source of systematic error is thorium the sensitivity of thorium being 2.3% of that of uranium. Results for USGS standard rocks are reported and the cost of the analysis is discussed.     

The determination of uranium and thorium in rocks by neutron activation analysis

A neutron activation method is described for the determination of thorium and uranium in rocks at the microgram and submicrogram levels. Radiochemical separations are carried out using the alpha-active nuclides protactinium-231 and neptunium-237 as tracers. The method is applied to the Standard granite XXX and the standard diabase XXX.     

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.     

Fast sensitive analysis of uranium and thorium in natural samples based on delayed neutron counting using an ultrafast conveyor tube system

A fast, sensitive and routine methode for quantitative analysis of uranium and thorium in natural samples is described. The identification is done by counting the delayed neutrons of mainly the short living fission products after sample-irradiation with and without cadmium shielding. The rabbit system used is installed at the Forschungsreaktor Neuherberg, type TRIGA Mark III. The limits of detection (relative to 2 g of sample weight) were specified to be 20 ppb (U) and 3 ppm (Th) using puls irradiations, 150 ppb (U) and 15 ppm (Th) using 1 MW steady state reactor power. A single determination is done within less than 60 s. The methods were proved by about 3000 measurements also including comparison experiments.     

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.     

Simultaneous determination of thorium and uranium in ores and SRMs by instrumental neutron activation analysis

A procedure has been developed for the determination of thoirum and uranium in ores and geological materials. The technique is relatively simple, accurate and adaptable routinely. Gamma-ray peak interferences are discussed in detail and the usefulness of the multiple gamma-ray peak ratios in the determination of the purity of peaks has been explained. The precision and accuracy of the method have been determined by analysing IAEA and NBL Standard thorium/uranium ores.     

Determination of uranium and thorium concentrations in some West Malaysian limestones using neutron activation and delayed neutron analysis

Concentrations of uranium and thorium in some West Malaysian limestones have been determined using neutron activation and delayed neutron analyses. These limestones are mainly calcium carbonates and contain uranium and thorium in concentrations of about a few parts per million.     

Fast and simple radiochemical method for the separation of uranium,thorium and lanthanum

The concept of using paper chromatography on papers impregnated with liquid anion or cation exchangers is extended to the separation of trace elements through filtration on filter papers loaded with suitable extractant. The uptake of uranium, thorium and lanthanum from HCl and HNO₃ media of different molarities by a filter paper treated with tri-octyl amine (TOA) is investigated. The effect of the different parameters on the uptake of the studied elements is experimented. A simple and fast radiochemical procedure is developed for the separation of La, Th and U from each other.     

Method for the determination of thorium and uranium in urine by ICP-MS

ICP-MS (inductively coupled plasma mass spectrometry) is shown as a very sensitive method for quantitative determination of Th and U concentration and excretion analysis in urine without any sample pretreatment. The current standard method for incorporation monitoring applies alpha-spectrometry, a very tedious and time consuming technique. ICP-MS offers an attractive alternative for monitoring of thorium and uranium body burdens in occupationally exposed subjects and also larger groups of the general population. A limit of determination of 0.5 ng/L in aqueous solutions and 1 ng/L in urine samples for both elements was achieved, with a precision of about ± 10% in the concentration range of appr. 10 ng/L. Due to the lack of a suitable reference material, the accuracy of the method was tested by comparing some of the results with those obtained by -spectrometry, especially for U. There was a sufficient agreement on both results.     

Biamperometric methodology for sequential determination of thorium and uranium

A biamperometric methodology for the sequential determination of thorium (Th) and uranium (U) was developed. In the sample solution containing Th and U, Th was first determined by complexometric titration based on the electrochemical behaviour of EDTA maintaining a potential of ≥200 mV between the twin Pt electrodes. This was followed by the redox titrimetric determination of U employing biamperometry to detect the end point. Prior to the determination of U, EDTA was destroyed by fuming with concentrated HClO₄ to eliminate its interference in the U determination. The method was tested for the determination of Th and U in (Th, U) O₂ samples containing 4 mg of Th and 2–8 mg of U, with precision and accuracy of better than 0.3 %.     

Determination of uranium and thorium in solar salts by neutron activation analysis

Uranium and thorium contents of solar salts were measured by neutron activation analysis. In advance of neutron irradiation, U and Th were concentrated and separated from some interfering elements by neutralization in which they were precipitated with aluminium hydroxide from solutions obtained by dissolving the salts in water or dilute nitric acid solution. The uranium and thorium concentrations determined were from several hundred ppt to 10 ppb. It was strongly indicated that uranium tends to remain in the solution (brine from seawater) phase in the process of solar salt production while thorium tends to transfer to the solid (solar salt) phase.     

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.