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.     

A simple method for the determination of uranium and thorium by delayed neutron counting

A simple method for the determination of uranium and thorium by delayed neutron counting is described. One portion of the sample is irradiated in a reactor and the delayed neutrons are counted. Another portion of the sample is mixed with B₄ C powder absorbing the thermal neutrons, and irradiated in the same position. From those data, both uranium and thorium can be calculated when a quantitative calibration has been made beforehand. The detection limits for the pure elements are 0.07 ppm for uranium and 2 ppm for thorium with the minimum analyzing time being 2 min. The accuracy of the method is investigated by comparing results obtained by the method described here with results obtained by epithermal activation analysis.     

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.     

Application of delayed neutron counting at CIAE

Journal of Radioanalytical and Nuclear Chemistry - Delayed neutron counting (DNC) was applied in quantitative determination of 235U/238U, quantitative determination of 235U and 239Pu in...     

Analysis of uranium using delayed neutron emission

Analyses of uranium and thorium by delayed neutron counting are described.The experimental system comprises an automatic pneumatic transfer system associatedwith a device made of twelve BF 3 neutron counters. Using homogeneous preparedsolutions of the samples, the analyses were based on a triple cycle each including60-second irradiation followed by 1-second cooling and 60-second counting.In these conditions, the limit of detection of uranium is about 0.3 µgwith a precision of measurement better than 10%. The contributions of possibleperturbations from 17 O(n,p)17 N reactions, followed by simultaneous –disintegration and neutron emission and from (n) reactions, have been studied.     

An automated delayed neutron counting system for mass determinations of special nuclear materials

An automated delayed neutron counting (DNC) system has been developed at the Royal Military College of Canada (RMC) to enhance nuclear forensics capabilities pertaining to special nuclear material analysis. The system utilises the SLOWPOKE-2 Facility at RMC as a neutron source and ³He detectors. System control and data acquisition occur through a LabVIEW platform. The time dependent count rate of the delayed neutron production has been examined for ²³⁵U, using certified reference materials. Experimental validation according to ISO 17025 protocols suggests typical errors and precision of −3.6 and 3.1%, respectively, and a detection limit of 0.26 μg ²³⁵U.     

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.     

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.     

Determination of uranium in NBS biological standard reference materials by delayed neutron assay

Uranium was measured in eight biological standards at the part-per-billion level. Matrix effects encountered in the use of liquid standards are discussed. This work performed under auspices of the U.S. Department of Energy     

An inexpensive automatic uranium and short-lived radioisotope analyzer

An inexpensive automatic pneumatic transfer system for uranium and thorium analysis by delayed neutron counting and for the activation analysis of short-lived radioisotopes has been developed, constructed and installed at the Nuclear Research Center Demokritos. Over 500 samples of solid uranium ore samples or liquid solutions of extracted uranium can be analysed daily by this system. Simplicity, safety, speed of operation, flexibility, sensitivity, accuracy and especially low cost are the main advantages of this analyzer. An improved version, with possibilities of cyclic activation analysis and faster capsule return times for very short-lived radioisotope analysis, is being developed.     

An elemental analyser system controller for data-processing of automatic C-H-N analysers

Summary An Elemental Analyser System Controller has been developed for automated data-processing of automatic C-H-N analysers. The elemental analyser system controller allows users, already in possession of a digital voltmeter or integrator, electronic microbalance, calculator and C-H-N analyser, to combine their various pieces of equipment into an automated system. After starting the C-H-N analyser, this system processes all data and calculates the blanks, calibration factors and percentages, successively. The operational modes of the principal parts of the element analyser system controller are described.

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Zusammenfassung Ein Kontrollgerät für Elementaranalysatoranlagen für automatisierte Datenverarbeitung automatischer C-H-N-Analysatoren wurde entwickelt. Bei Vorhandensein eines Digitalvoltmeters oder Integrators, einer elektronischen Mikrowaage, eines Rechengerätes und eines C-H-N-Analysators gibt dieses Kontrollgerät die Möglichkeit, die erwähnten Einzelteile zu einem automatischen System zu kombinieren. Nach Einschalten des C-H-N-Analysators verarbeitet dieses System nacheinander alle Daten, berechnet die Blindwerte, die Eichfaktoren und Prozentgehalte. Die Arbeitsweise der wichtigsten Teile des Kontrollgerätes wurde beschrieben.

     

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.     

An automated gamma-ray counting system for fast neutron activation analysis

An automated gamma-ray counting system was designed and built for use in counting long-lived nuclides (T>hr) produced during analysis by fast neutron activation. The system is mechanically simple, vet interfaced to sophisticated control and counting equipment for completely automated counting.     

Simultaneous determination of U and Th by delayed fission neutron technique based on neutron generator

A method for simultaneous determination of uranium and thorium based on the deviation of their fission cross-section curves has been developed. Using a D-T neutron generator two different neutron spectra were produced with and without moderator around the target. The detection limits were found to be 0.044 mg and 0.25 mg in the presence of a moderator, while for fast neutrons 0.017 mg and 0.037 mg for uranium and thorium, respectively.This work was supported in part by the Ministry of Higher Education and the Hungarian Academy of Sciences.