Determination of uranium element concentration and235U isotope abundance by neutron activation analysis

A new neutron activation technique has been developed for the determination of uranium element concentration and²³⁵U isotope abundance in nuclear safeguards and reference material samples based on the activation of bare and cadmium-covered samples with different thermal to epithermal neutron flux ratios and on the combination of the two corre-sponding delayed-fission neutron measurements. The principle of the new technique can be applied also to improve multi-element neutron activation analysis.     

Determination of trace elements in semiconductor materials by neutron activation analysis using the radioisotope addition technique

The determination of trace elements in highly activated matrix components was carried out by neutron activation analysis using the radioisotope addition technique. The method is based on the addition to the irradiated test sample of a radioisotope which is a diffeent nuclide of the element to be determined. After separation, the chemical yield is calculated from the radioactivity added and the element is determined by an ordinary technique. Twelve elements in indium phosphide and eight elements in gallium arsenide could be determined by the method.     

Monte Carlo calculations and neutron spectrometry in quantitative prompt gamma neutron activation analysis (PGNAA) of bulk samples using an isotopic neutron source

An activation analysis facility based on an isotopic neutron source (185 GBq ²⁴¹Am/Be) which can perform both prompt and cyclic activation analysis on bulk samples, has been used for more than 20 years in many applications including 'in vivo' activation analysis and the determination of the composition of bio-environmental samples, such as, landfill waste and coal. Although the comparator method is often employed, because of the variety in shape, size and elemental composition of these bulk samples, it is often difficult and time consuming to construct appropriate comparator samples for reference. One of the obvious problems is the distribution and energy of the neutron flux in these bulk and comparator samples. In recent years, we have attempted to adopt the absolute method based on a monostandard and to make calculations using a Monte Carlo code (MCNP4C2) to explore this further. In particular, a model of the irradiation facility has been made using the MCNP4C2 code in order to investigate the factors contributing to the quantitative determination of the elemental concentrations through prompt gamma neutron activation analysis (PGNAA) and most importantly, to estimate how the neutron energy spectrum and neutron dose vary with penetration depth into the sample. This simulation is compared against the scattered and transmitted neutron energy spectra that are experimentally and empirically determined using a portable neutron spectrometry system. This revised version was published online in August 2006 with corrections to the Cover Date.     

Application of neutron activation analysis in the investigation of trace element metabolism

The applications of neutron activation analysis in the investigation of trace element metabolism in animals and man are described and discussed. They include the determination of element distributions in the body, the study of correlations between trace element concentrations and physiological processes, the special methods of investigation of trace element metabolism in man and the identification of the chemical forms of the elements in the organism. Examples for each stage of application are given.     

Characterization of purified <Superscript>241</Superscript>Am for common impurities by instrumental neutron activation analysis

Americium is an important actinide element having versatile applications based on its alpha and gamma emissions. Multi-element determination of radioactive samples using ICP-AES technique may be affected by the presence of americium due to its rich emission spectra. With a view to characterize plutonium based fuels containing americium for trace metals by ICP-AES technique accurately, a high purity ²⁴¹Am (using a separation procedure developed in our laboratory) was prepared. To ascertain its chemical purity it is essential to determine its impurity contents accurately. Instrumental neutron activation analysis (INAA), being a sensitive multi-elemental technique, was employed to determine the concentrations of impurities in purified ²⁴¹Am. Detection limits for the common elements and rare earth elements have also been determined. Comparison is made with the analytical data obtained by the ICP-AES method.     

Multi-element standard for routine instrumental activation analysis of trace elements in rocks and tectites

The use of high-resolution Ge(Li) detectors in non-destructive instrumental neutron activation analysis (INAA) of mineral materials makes possible the simultaneous determination of a number of trace elements. In routine applications of INAA the use of a multi-element standard (MES) has proved to have advantages over a set of standards for each determined element. An MES has been prepared containing 8 trace elements mixed in a suitable proportion and giving, after neutron activation, long-lived γ-emitters, the γ-ray lines of which regularly occur in the γ-ray spectra of silicate mineral materials. This method has been used in the determination of Sc, Cr, Co, Rb. Cs, Eu, Hf and Th in samples of standard rocks and moldavites.     

Nuclear activation methods for the characterization of fossil fuels

A review is presented on the use of neutron activation analysis (NAA) for the analyses of coal, oil shale, tar sands and petroleum. Fast NAA has been widely used for the determination of oxygen, and to a limited extent, of other elements such as nitrogen and silicon. Reactor NAA followed by instrumental counting, and in specific cases, after radiochemical separations is discussed. Thermal and epithermal neutrons are both used. Limited use of the²⁵²Cf source has been made in fuel analysis. A complementary technique to NAA is the photon-activation analysis with linear accelerator. It can determine over thirty elements, many of them not possible to do by NAA. Round-robin analyses of standard coal, fly ash, or oil shale samples indicate nuclear activation methods are comparable in accuracy and precision to X-ray fluorescence or atomic spectrometric methods for most elements.     

Determination of trace elements in petroleum by neutron activation analysis

Using thermal neutron activation and a large-volume high-resolution Ge(Li) γ-ray spectrometer, the feasibility of the determination of the concentrations of Na, S, Cl, K, Ca, V, Mn, Cu, Ga, and Br in crude oils has been demonstrated. This instrumental method, which requires neither a chemical separation technique nor pre-concentration or post-concentration of trace elements by ashing, eliminates many inherent errors associated with chemical determination. The method is sensitive, precise and suitable for routine analysis. Fast neutron (n, p) and (n, α) reactions do not appreciably interfere and where necessary corrections may be applied. Loss of volatile elements, e.g. chlorine and bromine, due to recoil during irradiation is negligible.     

An Internal-Standard Method for Determination of Trace Impurities in Semiconductor Grade Silicon by Neutron Activation Analysis

An internal-standard method^1–4) has been applied for the determination of La, Sb, Au, Cr and Ag in silicon single-crystal by neutron activation analysis using cobalt as an internal-standard element. No chemical separation is required in this case and the precision obtained with the present method is satisfactory.     

A new technique for the 14 MeV neutron activation analysis of sodium and potassium

Cerenkov radiation produced in perspex by β and γ emitters may be readily measured by counting in the tritium channel of a liquid scintillation spectrometer, a technique which has interesting applications in neutron activation analysis. Further the fact that there are often considerable variations in the β energies of different radionuclides produced by activation means that by the use of suitable absorbers the determination of isotopes in a mixture is frequently possible. Such a method has been applied in the determination of a mixture of sodium and potassium. At the same time sensitivities and detection limits of the other alkali elements have been investigated and compared with results obtained from conventional gamma spectral analysis. Using such a technique it has proved possible to effect a considerable increase in sensitivity for the determination of sodium and potassium.     

Multielement analysis of Nigerian traditional (black) soaps

The element contents of some Nigerian traditional soap samples have been determined using thermal neutron activation analysis technique. The quality control consists of replicate analyses of standard 1632A bituminous coal for precision and accuracy determination. Potassium is found to be the major element in the soaps. While some elements show fairly constant concentration in all the samples analyzed, others have high maximum/minimum ratios. The elemental concentration variation in the soaps may likely have effects on their relative foaming capability and such variation is linked to the physical environment where the startingmaterials are obtained.To whom correspondence should be addressed at the Department of Chemistry, University of Ife, Ife-Ife, Nigeria.     

SIACON—Equipment for the on-line determination of the silicon content of coal

The paper describes an automatic equipment which allows to determine the silicon content of coal by neutron activation analysis. The technique is based on the measurement of gamma-ray intensity of the²⁸Al radionuclide, which is the result of the fast neutron reaction²⁸Si(n, p)²⁸ Al. The Activation part includes a Pu-238/Be neutron source which is located in the middle of the sample container; the measuring part includes two NaI(Tl)-scintillation counters. The total time of the anlysis of one sample amounts to a few minutes; the standard deviation of a single determination is 0.2% SiO₂.     

Prompt Gamma-Ray Activation Analysis: Fundamentals and Applications

Prompt gamma-ray activation analysis (PGAA) is an important nuclear analytical technique that complements conventional neutron activation analysis (NAA). When a target is placed in a beam of neutrons, gamma-rays emitted upon neutron capture are measured by a shielded germanium detector, yielding quantitative elemental analysis. The radiation is penetrating and the analysis both nondestructive and independent of the chemical form of the element(s) being measured. The technique is most useful for measurement of light elements (H, B, C, N, Si, P, S, Cl) which can not be easily measured by other methods. Best sensitivity is achieved with neutron beams from research reactors. Although sample preparation is minimal, care must be taken to select proper standards and blanks, and numerous corrections must sometimes be applied to the data from the complex spectra. PGAA has proven useful for multielement analysis of a wide variety of different materials spanning a broad range of scientific disciplines. Of particular importance has been the measurement of hydrogen in materials.     

Pulsed neutron-based on-line coal analysis

A neutron generator-based on-line coal analysis system is described, capable of measuring the content of the major and minor elements in coal. The system utilizes reactions produced from fast and themal neutrons, as well as from neutron activation with half lives of seconds or minutes. Characteristic γ-rays, detected with BGO detectors are used for the identification of the various chemical elements. The method for the analysis of the γ-ray spectra is presented, and the measurements of coal density, carbon and sulfur content are shown.     

A rapid radiochemical procedure for uranium determination in natural waters

A neutron activation analysis method for the determination of uranium in natural fresh waters is described. The method is based on a preconcentration step by precipitation of the metal oxinate on a phenolphtalein bed followed by instrumental neutron activation analysis. Preliminary investigations with²³⁹U radiotracer were carried cut to set up the best working conditions and to evaluate the chemical yield. The whole procedure has been applied to the determination of uranium in river water.     

INAA of toxic elements in coal and their transfer into environments

An instrumental neutron activation analytical (INAA) technique is described for the determination of 26 toxic and other trace elements in Eastern Coal (NBS SRM-1632a), local coal and its ash. The coal ash was produced by heating coal at 750°C in a muffled furnace. The transfer of these elements to the environment on the complete compustion of coal is estimated from the difference between the elemental concentration of coal and its ash.     

Determination of chromium,manganese, lead and cadmium in biological samples including hair using direct electrothermal atomic absorption spectrometry

Direct analysis of solid samples employing a laboratory assembled electrothermal atomic absorption spectrometer is demonstrated to be a feasible approach for determination of trace elements in plant tissue and hair samples for special applications in plant physiology and biomedical research. As an example, the kinetics of Cr uptake by cabbage and its distribution have been measured as a function of chromium speciation in the nutrient solution. Further, longitudinal concentration gradients of Cr, Pb and Cd have been measured in hair of various population groups exposed to different levels of these elements in ambient and/or occupational environments. The techniques are validated for the determination of these trace elements by neutron activation analysis, dissolution atomic absorption spectrometry and by analysis of certified reference materials. Slurry sample introduction is found appropriate for routine trace element determination and in homogeneity testing. Direct sample introduction is indispensable in the analysis of very small (< 1 mg) tissue biopsy samples in the determination of trace element distributions.     

A technique for improved detection limit in indirect neutron activation determination of boron

Using vanadium as the activable element, an indirect cyclic neutron activation technique for determination of boron in aqueous solutions has been developed. Experimental arrangement consisted of a 5 Ci Pu?Be based neutron irradiator and a 7.5 cm × 7.5 cm NaI/Tl/ detector. Recycling of vanadium between the irradiation source and the detector produced improved detection limit and sensitivity.