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.     

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.     

An automated neutron activation system for short-lived nuclides

The present paper describes an attempt to create a reliable and easy to use system for neutron activation with short-lived nuclides, suitable to be used with several irradiation and counting procedures in instrumental neutron activation analysis (INAA) at the Portuguese Research Reactor. This system can become very useful for a large community within LNETI, as well as other national institutes and universities, particularly for those involved in studies where the analysis of a large number of samples is required. Selenium determination has been performed, through the short-lived nuclide^77mSe, as an example of the reliability of the system.     

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...     

The use of delayed nuclear track counting for determining bismuth

The predominant use of the nuclear track technique (NTT) in analytical chemistry has been to measure the prompt charged particle emission from neutron induced reactions with stable or fissile nuclides of selected elements. This work describes the use of the NTT for determining bismuth via delayed alpha particle emission from the decay of²¹⁰P. This technique is sensitive and reliable since alpha track counting is highly efficient and can provide information, on elemental spatial distributions. Bismuth determinations in various materials by this technique appears possible to at least the 1.0 microgram per gram level.     

An automated facility for neutron activation analysis

A fully automated neutron activation analysis (NAA) facility has been constructed at the Whiteshell Nuclear Research Establishment. This high-capacity facility has been designed for use with a wide variety of neutron sources, including Canada's SLOWPOKE II and MAPLE research reactors. Its pneumatic transfer system is driven by a Square-D Model 500 programmable controller, linked in turn to a Nuclear Data ND6700 computer/spectrometer. Custom software for data entry and system control has been combined with Nuclear Data software for gamma-spectrum acquisition and processing to create a flexible, easy-to-use facility for NAA. Its design and performance are discussed.     

Application of neutron activation analysis for trace element determinations in biological materials

Over the past three decades, more and more interest has been focused on trace eleemnts in biological materials. This increasing interest has gone hand in hand with the continuous improvement of analytical techniques. Neutron activation analysis has proven to be a most suitable method for the quantitative determination of a wide variety of trace (0.01–100 μg g^?1) and ultratrace (<0.01 μg g^?1) elements in biological materials. This technique has even played a preponderant role in this field.     

Reference materials for USFDA's whole-body counting system

The U.S. Food and Drug Administration (FDA) operates a whole-body counter at its's Winchester Engineering and Analytical Center (WEAC), Winchester, MA. This counter has been registered with the International Atomic Energy Agency (IAEA) and has been made available to others. The new requirements of the Nuclear Regulatory Commission (NRC) include internal dose exposure, using such a system. The whole-body counter performs thyroid scans for iodine-131 and also for iodine-125 and iodine-123. The latter requires thin-window germanium detectors (X-ray spectrometers). In addition, it has a large sodium iodine (Tl) crystal for whole body scans. One of the problems has been developing reference standards for energy and efficiency calibrations. Up to recently, only phantoms have been available to which the radioactive solution must be added. Lately, the Department of Energy has developed a loan program of phantoms containing specific radioactive isotopes in various configurations. This is expected to be added to this program to confirm the measurements. Software has also been developed which will calculate a 50 year dose commitment as required by the NRC for exposures. The use of these reference materials to assure that the system is in calibration is discussed.     

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.     

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.     

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.     

An automated neutron activation procedure for screening PCB content of oil

An analytical procedure for rapidly screening large numbers of oils for polychlorinated biphenyl (PCB) content has been developed and is now in routine use. Pontential levels of PCBs are inferred from chlorine concentrations as determined using the automated neutron activation analysis (NAA) facility at the Los Alamos National Laboratory Omega West Reactor. The technique is designed to screen up to 200 oil samples per eight hour working day, using a sample volume of approximately 1 milliliter. Because of the automated nature of the analysis, elements in addition to chlorine are determined, when present. These include fluorine, bromine, iodine and sulfur. U.S. National Bureau of Standards (NBS) and U. S. Environmental Protection Agency (EPA) Standard Reference Materials are routinely analyzed for quality assurance purposes. The results of our analyses of these materials for certified elements is discussed as well as results for other non-certified elements observed in the standard materials.     

Validation of a loss-free counting system for neutron activation analysis with short-lived indicators

The use of loss-free counting systems makes possible the exact correction for pile-up and dead-time losses during counting of a mixture of short-lived radionuclides even at very high count rates. However, counting statistics cannot be calculated by taking into account only the Poisson distribution of the incoming -quanta, such as is done in existing computer programs for -spectrometry. At moderate count rates Müller statistic was found to account for the observed variability between duplicate countings; however, at higher count rates the variability of weighing factors was found to be significant in comparison with the Müller statistic. While counting statistics could not be correctly estimated for short-lived species, experiments showed excellent accuracy for initial dead times up to 90%.     

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.     

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.     

An absorbance-based micro-fluidic sensor for diffusion coefficient and molar mass determinations

The H-Sensor reported herein is a micro-fluidic device compatible with flow injection analysis (FIA) and high performance liquid chromatography (HPLC). The device detects analytes at two separate off-chip absorbance flow cells, providing two simultaneous absorbance measurements. The ratio of these two absorbance signals contains analyte diffusion coefficient information. A theoretical model for the sensing mechanism is presented. The model relates the signal Ratio to analyte diffusion coefficient. The model is qualitatively evaluated by comparing theoretical and experimental signal Ratio values. Experimental signal Ratios were collected via FIA for a variety of analytes, including sodium azide, benzoic acid, amino acids, peptides, and proteins. Measuring absorbance at multiple wavelengths provides higher order data allowing the analyte signals from mixtures to be deconvolved via classical least squares (CLS). As a result of the H-Sensor providing two simultaneous signals as a function of time for each sample injection, two simulated second-order HPLC chromatograms were generated using experimental H-Sensor data. The chemometric deconvolution method referred to as the generalized rank annihilation method (GRAM) was used to demonstrate chromatographic and spectroscopic deconvolution. GRAM also provides the signal Ratio value, therefore simultaneously obtaining the analyte diffusion coefficient information during deconvolution. The two chromatograms successfully serve as the standard and unknown for the GRAM deconvolution. GRAM was evaluated on chromatograms at various chromatographic resolutions. GRAM was found to function to a chromatographic resolution at and above 0.25 with a percent quantitative error of less then 10%.