Determination of Trace Elements in Liquid Fuels by Instrumental Neutron Activation Analysis

Abstract

An instrumental neutron activation analysis with Ge(Li) γ -spectrometry and computer-assisted data reduction, has been developed for the determination of more than 20 elements in different liquid fuels. Organo-metallic standard solutions were mixed to obtain suitable standards. Two neutron irradiations and 4 γ-spectrometric measurements are required for each sample. Corrections were taken into account for a few spectrometric and nuclear interferences. The overall standard deviation for nearly all elements is mainly determined by counting statistics. The following elements can be determined : Na, Al, S, Cl, K, Sc, V, Cr, Fe, Co, Ni, Cu, Zn, As, Se, Br and La whereas the concentration of the following elements are mostly near the limit of detection: Mg, Mo, Sb, Ba, Th and Hg.     

Multielement determination in water by instrumental neutron activation analysis

Instrumental neutron activation analysis /INAA/ technique has been applied to a water sample to determine the elemental concentrations. The sample was irradiated with a neutron flux of 1.2×10¹² n cm^–2 s^–1 for two different periods followed by counting at three different decay times, using two coaxial type high-resolution Ge/Li/ detectors. The dominant elements determined in the water sample are Ca, Cl, Na, Mg, and K present in ppm-level while Co, I, Mn, Sm, and Sb are present in smaller amounts, approximately on the average 0.01 ppm. Only traces of other elements such as the rare-earth elements, Ag, As, Ba, Cu, Cd, Fe, Sr, W, Zn, seem to be present in the water sample.     

Pattern recognition analysis for characterization of coal and ash samples

Different pattern recognition techniques were applied for classification and characterization of a large number of coal, and coal fly ash samples. Cluster analysis was performed on 116 samples using the concentration data of 40 elements. The effect of the number and type of the elements on the clustering was studied in detail. It was proved that short time activation analysis enables the characterization of these types of samples if¹³⁹Ba and⁸⁷Sr are included, these data being obtained by increasing the irradiation and counting times. The two elements and chlorine were found to be necessary for such a classification. The combination between cluster analyses and principal component analysis gives accurate and confirmed results. The statistical analyses of the subgroups are compared.     

Determination of uranium by thermal and epithermal neutron activation in natural waters and in human urine

Uranium is determined via its ²³⁹U nuclide (74.0 keV, t_{$\text{1}\text{2}$} = 23.5 min) in natural waters down to 0.03 ng U ml^-1 after preconcentration with activated carbon and oxine; 30-min irradiation and counting times are used. No preconcentration is required for samples containing more than 4 ng U ml^-1 with 10-min irradiation and counting times. Uranium in urine can be determined under a boron shield at the 5 ng ml^-1 level after 30-min irradiation and counting.     

Comparison of 125I-Labeled and 14C-Labeled Peptides of the Major outer Membrane Protein of Chlamydia Trachomatis Strain L2/434 separated by High-Performance Liquid Chromatography

Abstract

The objective of this study was to determine if in-gel chloramine-T radioiodination adequately labels OM proteins to allow for accurate and precise structural comparison of these molecules. Therefore, intrinsically ¹⁴C-amino acid labeled proteins and ¹²⁵I-labeled proteins were cleaved with two endopeptidic reagents and the peptide fragments separated by HPLC. A comparison of retention times of the fragments, as determined by differential radiation counting, thus indicated whether ¹²⁵I-labeling identified of all the peptide peaks seen in the ¹⁴C-labeled proteins. Results demonstrated that radioiodination yields complete and accurate information about the primary structure of outer membrane proteins. In addition, it permits the use of extremely small amounts of protein allowing for method optimization and multiple separations to insure reproducibility.     

Some Aspects of Analysis of Single Fibers in Environmental and Biological Samples

Abstract

Nuclepore filters were used for sampling and evaluation of fibrous particles in ambient air, in liquids and in biological materials. The fiber counting and fiber size measurements were done by means of SEM-methods. The number of fibers and the distributions of fiber lengths and diameters were plotted. The specific identifications of asbestos, glass and other mineral fibrous particles were made by electron microprobe analysis. Certain elements proved to be approximative identification factors for different fibrous minerals in ambient air, in liquids, on material surfaces, or in biological materials.

For ambient air, asbestos, glass, and many other inorganic fibrous particles were found in the urban atmosphere as well as in the atmosphere of remote regions. Fibrous gypsum, fibrous ammonium sulfates, fibrous silicates, fibrous mica, and quartz were identified among these particles. Even in remote ambient air, relatively high concentrations of inorganic fibrous particles could be measured.     

Radiochemical Analysis of 35SO2 Adsorbed on Pbo2

Abstract

The concentration of ³⁵SO₂ in air can be measured by reacting with Pbo₂ to form Pb³⁵SO₄. A method was developed which is suitable for rapid, high-protection radioassaying of ³⁵SO₄ ^2- on the surface of Pbo₂. The surface ³⁵SO₄ ^2- was extracted with a quaternary alkylammonium hydroxide in toluene and counted in an organic liquid scintillator solution with an efficiency of approximately 94%, which was constant for 30 days when corrected for natural decay. More than 99.5% of the surface sulfate was extracted in less than 5 minutes for quaternary alkylammonium concentrations 600 times in excess. This technique was shown superior to gas-flow proportional counting of the PbO₂ surface.     

Multielemental determination in water by neutron activation analysis

Instrumental neutron activation analysis (INAA) technique has been applied to a water sample to determine the elemental concentrations. The sample was irradiated at a neutron flux of 1.2·10¹² n·cm^–2·s^–1 for two different periods followed by counting at three different decay times, using two coaxial type high-resolution Ge(Li) detectors. The dominant elements detected in the water sample are Ca, Cl, Na, Mg, and K present in levels while Co, I, Mn, Sm, and Sb are present in smaller amounts approximately on the average 0.01 ppm. Only traces of other elements such as rare-earth elements, Ag, As, Ba, Cu, Cd, Fe, Sr, W, Zn, seem to be present in the water samples.     

Precise determination of isotopic ratios for some biologically significant elements by inductively coupled plasma mass spectroscopy

Isotope ratios for copper, iron, lead, lithium, nickel and zinc were measured with an ELAN 5000 ICP-MS instrument. Except for lithium isotopes, ratio relative standard deviations (RSDs) of about 0.1% were achieved with measurement times of 10 min or less per sample on isotope pairs that differed by no more than a factor of 10 in abundance. It was necessary to accumulate several million counts to reduce statistical counting errors, to correct for the dead time in the counting circuitry, and to compensate for a slow drift of apparent ratios with time. Drift compensation was achieved by using a third isotope of the test element, by adding two internal standard elements with isotopes bracketing the mass range of interest, or by frequent recalibration with a standard of known abundances. Attempts to compensate for drift in lithium isotope ratios were not successful and typical RSDs for ⁶Li/⁷Li remained around 0.5%. Copper and zinc ratios were measured in pig feces with ratio precision and drift behavior essentially identical to that seen for synthetic solutions.     

Development of the <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-based cyclic neutron activation analysis for short-lived radionuclides

The k ₀-based cyclic neutron activation analysis (k ₀-CNAA) technique has been studied to explore the applicability at the Portuguese research reactor (RPI). In particular, for the determination of elements which form short-lived radionuclides, particularly fluorine (²⁰F, 11.16 s half-life) and selenium (^77mSe, 17.36 s half-life) in polymer, biological and environmental samples. The detection limits obtained for F and Se were about 50 and 0.01 mg kg⁻¹, respectively, in the investigated materials. The timing parameters for the procedure were 10 to 20 s for irradiation, 5 s decay, 10 to 20 s counting, 5 s waiting and performed with eight cycles. The k ₀-IAEA program was modified to use millisecond time resolution for irradiation, decay and counting times as needed for interpreting k ₀-CNAA data in terms of concentration, accuracy and detection limit. The quality control of the procedure was performed by preparing a standard solution containing fluorine with different contents as well as using the certified reference materials containing selenium from which the bias between the results and the certified values were within 15% for most elements at the investigated content ranges. The analytical results for several other elements producing short-lived or detectable radionuclides, e.g., Al, Ca, Cl, Cu, Dy, I, Mg, Mn, Ti, and V were also obtained by the k ₀-CNAA procedure with accuracy within 12%.     

Analysis of Resin-Bead Loaded U And PU Samples with a Single-Stage Mass Spectrometer

Abstract

The resin bead sample loading technique has been applied to a conventional single-stage mass spectrometer equipped with pulse counting. Isotopic data obtained for U and Pu are comparable to those obtainable from similar instruments using conventional techniques.     

Simultaneous Plutonium and Uranium Isotopic Analysis from a Single Resin Bead - A Simplified Chemical Technique for Assaying Spent Reactor Fuels

Abstract

The method uses basic anion resin to adsorb plutonium and uranium from 7–8 M HNO₃ solutions containing dissolved spent reactor fuels. After equilibrating the resin with the solution, a single bead is used to determine the isotopic composition of plutonium and uranium on sample sizes as small as 10^?9 to 10^?10 g of each element per bead. Isotopic measurements are essentially free of isobaric interferences and fission product contamination in the mass spectrometer is eliminated. A very small aliquot of dissolver solution containing 10^?6 g of U and 10^?8 g of Pu is sufficient sample for chemically preparing several resin beads. A single prepared bead is loaded onto a rhenium filament and analyzed in a two-stage mass spectrometer using pulse counting for ion detection to obtain the high sensitivity required. Total quantity of the elements, in addition to isotopic abundances, can be determined by isotope dilution. Other areas where the method may be useful are: in plutonium production, isotope separations, and for trace detection of contamination on reactor parts.     

Limit of the INAA procedure for copper determination based on the64Cu 511 keV line

The²³⁵U/²³⁸U ratio is determined by neutron activation analysis counting the ϕ-rays of short half-lives fission products and²³⁹U. The effect of the neutron spectrum hardening using a⁶LiD converter is also demonstrated. The²³⁵U/²³⁸U ratio is determined using short irradiation, waiting and counting times.     

On-stream nuclear activation of trace uranium and thorium using a 14 MeV neutron generator

A method for the continuous on-stream determination of trace concentrations of uranium and thorium in flowing streams is developed. The 14 MeV neutron generator was used for irradiation and the delayed neutron counting technique was employed in counting the induced neutron activity. The dependence of the minimum detectable concentration on the irradiation, decay and counting times, liquid flow-rate and the background was studied. At optimal conditions, uranium and thorium concentrations were determined down to 20 and 100 ppm, respectively. The interference of the neutron emitting nuclide^17m O was reduced to an insignificant level by optimizing the decay time.     

Continuous Blood Monitoring of Hard Beta-Emitting Isotopes in Small Laboratory Animals

Abstract

A monitoring system for recording very fast variations in blood levels of ³²P-labeled compounds is described. The flow-cell used is suitable for continuous determinations in anesthetized small laboratory animals (e.g. rats). The technique reported has been developed for hard beta-emitting isotopes. However, changing the counting unit, the described flow-cell can be adapted for gamma-emitting isotopes. With our system, efficiencies of the order of 40% have been obtained for ³²P in whole blood.     

Plutonium Activity Ratios in Plankton: New Evidence of Hold-Up Time in Irish Sea Sediments

The determination of activity ratios for radioisotopes of different half-lives can be used to estimate transit times from a point source to locations further away. For conservative elements, this time is approximately equivalent to the net hydrological transport. However, for non-conservative elements such as plutonium, the additional influence of biogeochemical processes decreases the net transport time. In this study, ²⁴¹Pu and ^239,240Pu concentrations in Irish Sea plankton samples, collected in May 1994, were determined and the ²⁴¹Pu/^239,240Pu ratios calculated. Plutonium-239,240 was measured using a standard method by ion exchange chromatography and alpha counting, and ²⁴¹Pu was determined by liquid scintillation counting using the disk-supported technique. The latter showed some methodological problems, which are briefly discussed. The ²⁴¹Pu/^239,240Pu ratios gave an estimate of the "transit time" from Sellafield to the different sampling points. In fact, this time represents the age of plutonium in plankton, i.e., the time lag between release from Sellafield and detection at the different sampling stations. The mean plutonium age was 17±2 years (n = 10) and 18.6±0.8 years (n = 13) in phytoplankton and zooplankton, respectively. The spatial distribution was reasonably homogeneous over the Irish Sea. The assimilation-elimination processes of plutonium in plankton are rather rapid. Therefore, it may be assumed that, in this time scale, the plutonium concentrations were in equilibrium with surrounding waters. Thus, it is concluded that plutonium was rather old because resuspension-sedimentation processes had occurred that delayed its transport within the Irish Sea. Therefore, the age of plutonium in plankton represented the hold-up time of plutonium in the sediments from the Irish Sea.     

Measurement of <Superscript>3</Superscript>H,gross <Emphasis Type="Italic">α/β</Emphasis> and <Superscript>222</Superscript>Rn in drinking water using the new Quantulus GCT 6220

Since the introduction of the European Council Directive 2013/51 Euratom in October 2013, the analysis of drinking water has increasingly become the focus of many laboratories in Europe. The activity of tritium, radon and the gross α/β-activity is determined routinely. In order to cope with the increased sample numbers and to reach the necessary detection limits, sensitive measuring devices are required. This work was done with the new Quantulus GCT 6220 to test the sensitivity of this system for drinking water analysis. The results indicate that this instrument is very well suited for this type of analysis and counting times are typically below the required counting times of established systems.     

Fluorimetric Determination Of Selenium In Marine Geological Materials

Abstract

Acid decomposition with nitric, perchloric and/or hydrofluoric acids is used to extract selenium from marine geological materials. Selenium is isolated from potentially interfering elements by coprecipitation with lanthanum hydroxide, then a piazselenol is formed between 2, 3-diaminonaphthalene at pH 1.0 and extracted into cyclohexane. The selenium is determined fluorimetrically in the extract. The detection limit is 3.2 ng (four times the standard deviation of blank) and the coefficient of variation is 5% at the 10 ng level. The sample decomposition procedure is evaluated and typical results obtained for selected samples are given.     

Multiparameter Coincidence Spectrometry Applied to the Non-Destructive Neutron Activation Analysis of Meteorites

Abstract

A non-destructive method for the neutron activation analysis of chondritic meteorites by multiparameter coincidence spectrometry is described. Results for sodium, cobalt, nickel and iridium are presented, and agree with single coincidence spectrometry measurements. Scandium photopeaks are prominent in the multiparameter spectrum and this element could also be determined. The advantages of multiparameter spectrometry over single coincidence counting are outlined.     

Self-assembled vesicles from amphiphilic platinum(II) terpyridyl complex in water

A new cationic amphiphile (1) functionalised with platinum(II) terpyridyl unit was designed and synthesised to realize self-assembly in water. Using UV–vis and emission spectroscopy, scanning electron microscopy, cryogenic transmission electron microscopy, dynamic light scattering and time-correlated single-photon counting technique, we have demonstrated that amphiphile 1 can self-assemble into stable vesicular aggregates upon direct dissolution in water, which is rarely observed in the literature.