Analysis of high-purity material—A comparison of photon activation analysis with other instrumental methods

Photon activation analysis (PAA) has been a well-established analytical method for about two decades. In this paper, its particular features are outlined in comparison with other modern instrumental techniques, especially radioanalytical methods, e.g. activation analysis with thermal or fast neutrons (NAA) or charged particles (CPA). Emphasis is placed upon the determination of trace components of high-purity material; iron, copper and lead matrix were selected as examples. In PAA, both instrumental and radiochemical procedures were applied. The results are presented in comparison with those obtained by other laboratories using a large variety of different techniques.     

Determination of chromium, iron and cobalt in high-purity niobium by radiochemical neutron activation analysis

Summary Chromium, iron and cobalt were determined in niobium by radiochemical neutron activation analysis. The main steps of the technique involved the irradiation of the samples in a medium or high-flux reactor, the post-irradiation decontamination of the sample surface, a two-step separation procedure based on anion-exchange from HF and HCl medium, and counting the separated indicator radionuclides with a well-type NaI-detector. For a 42-day irradiation at a thermal neutron flux of 8×10¹³ n cm^–2 s^–1 and a sample weight of 100 mg, the limits of detection are: 10 ppt for chromium, 1.5 ppb for iron and 4 ppt for cobalt. The results obtained by this technique are compared with data obtained by radiochemical proton activation analysis and atomic absorption spectrometry.

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Bestimmung von Chrom, Eisen und Cobalt in hochreinem Niob durch radiochemische Neutronenaktivierungsanalyse

Zusammenfassung Die Hauptschritte der Methode sind die Bestrahlung der Probe in einem Mittel- oder Hochflußreaktor, eine anschließende Oberflächendekontamination und die spezifische Abtrennung der Indicatorradionuklide mittels Anionaustausch aus Flußsäure- und Salzsäure-Medium, sowie die Messung der Radionuklid-Fraktionen mit einem Natriumjodid-Detektor.Für eine 42tägige Bestrahlung mit Reaktorneutronen bei einem thermischen Fluß von 8×10¹³ n cm^–2 s^–1 konnte bei einem Probengewicht von 100 mg für Chrom eine Nachweisgrenze von 10 ppt, für Eisen von 1,5 ppb und für Cobalt von 4 ppt erreicht werden.Die mit dem Verfahren erhaltenen Ergebnisse werden mit denen der radiochemischen Protonenaktivierungsanalyse und der Atomabsorptions-Spektrometrie verglichen.

     

Determination of selenium in human diets by radiochemical neutron activation analysis.

A post-irradiation radiochemical separation technique was tested for the determination of selenium levels in diet samples, collected by using a duplicate portion technique, from both rural and urban population groups in Turkey. The technique involved sample irradiation, acid digestion, selective distillation, precipitation and filtration steps. During the separations it was possible to determine the yield of each sample using a stable selenium carrier. An average chemical yield of 71 +/- 3% was obtained for the radiochemical neutron activation analysis. For samples from urban and rural regions, the average selenium concentrations obtained were 0.14 +/- 0.04 and 0.07 +/- 0.02 mg kg-1, respectively. It was also possible to determine daily dietary selenium intakes, which were found to be 81 +/- 41 micrograms and 23 +/- 11 micrograms for the urban and rural groups, respectively. Although daily selenium intakes were found for a small number of subjects in this study, the separation technique developed can be used for determination of the selenium status in larger population groups.     

Determination of gold in gold ores

The gold content of placer gold flakes and gold bearing ores has been determined by instrumental neutron activation analysis /INAA/ and radiochemical neutron activation analysis /RNAA/. It was discovered that significant errors result in the instrumental method for gold flakes as small as 10 mg due to sample self-absorption of neutrons during irradiation. Reliable results were obtained, for both ore samples and gold flakes, by dissolving the samples in aqua regia prior to irradiation.     

Simultaneous determination of iodine and selenium in biological samples by radiochemical neutron activation analysis

Summary Regarding the favourably sensitive nuclear characteristics of iodine and of selenium but the very different half lives of their induced nuclides ¹²⁸I and ⁷⁵Se, a radiochemical neutron activation analysis method for simultaneous determination of these elements in a single sample was developed. It is based on the double irradiation LICSIR technique — Long Irradiation for Se (40h), Cooling (a week or more), Short Irradiation for iodine (1–15 min) with following Radiochemistry. After the second short irradiation, the sample is ignited in an oxygen flask and iodine and selenium are sequentially and selectively extracted as elemental iodine and 5-nitro-2,1,3 benzoselena diazole chelate. With the described method biological samples were analysed and the reliability of the results was checked by the analyses of different standard reference materials. Good agreement with certified values and high radiochemical purity of the spectra show the applicability of the radiochemical separation developed.     

Determination of major and trace elements in iron reference materials using k0-NAA

Major and trace element contents in iron ore reference materials were investigated using k ₀-instrumental neutron activation analysis (k ₀-INAA). To avoid iron interferences, radiochemical separation was developed (k ₀-RNAA). The determination of the investigated elements in the inorganic phase from hydrochloric acid solution was performed after radiochemical separation of iron by diisopropyl ether. It was found that after the Fe elimination, the limit of detection for some elements was much lower that enables their direct determination. The distribution of 39 elements (with intermediate/medium and long half-life radionuclides) after Fe removal was investigated.     

Determination of rare earth elements in recent and fossil shells by radiochemical neutron activation analysis

Seven rare earth elements (La, Ce, Sm, Eu, Tb, Yb and Lu) in marine shell samples were determined by neutron activation analysis. In order to measure γ-ray using a Ge(Li) detector without serious interference from the intense Compton background from²⁴Na, a simple radiochemical separation was performed by a co-precipitation method with hydrated iron(III) oxide. The chemical yields for shell samples (91–99%) were determined by a re-activation technique for Gd and Yb. The interference from the²³⁵U(n, fission) reaction was corrected for determination of La and Ce. The data obtained in this study showed the behavior of rare earth elements in shells during the process of fossilization.     

Phosphorus determination in milk and bone samples by neutron activation analysis

The determination of phosphorus in milk and bone samples by both radiochemical and instrumental neutron activation analysis is described. The radiochemical method consists of thermal neutron irradiation of samples and standards, sample dissolution, phosphorus precipitation as ammonium phosphomolyb-date, use of zinc holdback carrier and counting of the phosphorus-32 ß-activity. The instrumental method involves thermal neutron irradiation of samples and standards, waiting for a decay time and ß-counting. The methods were applied to commercial samples and reference materials.     

Multivariate optimization of a microwave-assisted leaching procedure using dilute acid solutions,for FAAS determination of Cu,Fe, Mn,and Zn in multivitamin/multimineral supplements

This paper reports the development of a microwave-assisted procedure for leaching of copper, iron, manganese, and zinc from multivitamin/multimineral supplements by use of dilute acid before determination by flame atomic absorption spectrometry (FAAS). A Doehlert design was used to find optimum conditions for the procedure by use of response-surface methodology. Three variables (acid concentration in the leaching solution, irradiation time, and irradiation power) were used as factors in the optimization study for two acids, HCl and HNO₃. Final working conditions were established as a compromise between the optimum values for each analyte, taking into consideration the robustness of the procedure. The best leaching results were obtained with HNO₃ and the acid concentration, irradiation time, and irradiation power used were 0.70 mol L⁻¹, 15 min and 360 W, respectively. The accuracy of the optimized procedure was evaluated by comparison with a well-established closed-vessel microwave dissolution technique.     

The determination of molybdenum in geological samples by Neutron Activation Analysis

A metal-silicate extraction technique combined with neutron activation analysis has been developed to determine molybdenum in geological samples. The samples are equilibrated with Femetal powder at high temperatures. Molybdenum is completely extracted into the metal phase because of very reducing conditions in the furnace. The metal spherule is separated from the silicates, irradiated and dissolved in an acid solution. The molybdenum is precipitated as a sulfide and the precipitate is dissolved in aqua regia and counted on a Ge/Li/detector. The radiochemical yield is obtained by irradiation of the solution. The method avoids production of⁹⁹Mo from induced fission of²³⁵U by performing the metal-silicate separation before irradiation. The precipitation step may be necessary to remove the high background from the decay of⁵⁹Fe. Mo concentrations down to 15 ng/g have been obtained using this method.     

The Determination of Co in Plant Materials by Radiochemical Neutron Activation Analysis

The influence of irradiation conditions on the results of Co determination in plant samples by radiochemical neutron activation analysis (RNAA), after the conventional and microwave assisted wet digestion, has been investigated. Nine CRMs of botanical origin were examined. The study has demonstrated that the effectiveness of mineralization depended significantly on the kind of sample and the irradiation conditions. When analyzed CRMs were subjected to long-term irradiation in a high neutron flux, the mineralization using the microwave technique was necessary to obtain the correct results of Co determination in some of the plant samples. It has been proved that microwave digestion in a mixture of HNO₃+H₂O₂+HF should be a standard method of wet ashing, independent on matrix and irradiation conditions.     

Preparation of carrier-free radionuclides from cyclotron targets by continuous electrophoresis,I

Continuous electrophoretic separation of the components of the manganese, iron, copper and silver cyclotron targets bombarded with deuterons is described. The rates of separation were: managanese target, 4.4 mg Mn/hr; iron target, 1.5 mg Fe/hr; copper target, 1.7 mg Cu/hr; and silver target, 6.7 mg Ag/hr. The radionuclides were separated in carrier-free form and were of high radiochemical purity. The results are represented by radioautographs of the continuous electrophoretic processes, and by diagrams showing the distribution of the target material and of radioactivity along the collecting glasses. The radiochemical purity of the separated radionuclides was checked by the gamma spectra, by estimation of the beta-energies, and by evaluation of the decay curves.     

Korrekturen bei Neutronenaktivierungsanalytischen Elementbestimmungen bei Wechselndem Bestrahlungszyklus und Verwendung der Mono-standard-methode

The described method is suitable for the determination of about 20 trace-elements by neutron activation analysis and radiochemical group separation with one standard (flux-monitor) instead of the simultaneous irradiation of the elements investigated. The activity of the flux-monitor delivers the correction-factor, under the same irradiation conditions (neutron spectrum), between the irradiation of a complete standard-set and the different irradiations of unknown samples. The FRN (Research Reactor Neuherberg) is not working continuously so that it is necessary to add different irradiation times of some hours to our routine irradiation time of 24 hours. The correction factors for these complicated working conditions in neutron activation analysis are mathematically described and discussed.      

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.     

Photon and proton activation analysis of iron and steel standards using the internal standard method coupled with the standard addition method

The internal standard method coupled with the standard addition method has been applied to photon activation analysis and proton activation analysis of minor elements and trace impurities in various types of iron and steel samples issued by the Iron and Steel Institute of Japan (ISIJ). Samples and standard addition samples were once dissolved to mix homogeneously, an internal standard and elements to be determined and solidified as a silica-gel to make a similar matrix composition and geometry. Cerium and yttrium were used as an internal standard in photon and proton activation, respectively. In photon activation, 20 MeV electron beam was used for bremsstrahlung irradiation to reduce matrix activity and nuclear interference reactions, and the results were compared with those of 30 MeV irradiation. In proton activation, iron was removed by the MIBK extraction method after dissolving samples to reduce the radioactivity of⁵⁶Co from iron via⁵⁶Fe(p,n)⁵⁶Co reaction. The results of proton and photon activation analysis were in good agreement with the standard values of ISIJ.     

Determination of chlorine in silicate rocks by neutron activation analysis

A simple radiochemical neutron activation analysis scheme has been developed for the determination of chlorine in silicate rocks. The method involves a 15-min thermal neutron irradiation of rock powder followed by a quick separation of ³⁸Cl as AgCl, and Ge(Li) spectrometry. Chemical yield, normally ranging between 95% and 100%, is monitored gravimetrically through the recovery of AgCl. The procedure has been tested on several geochemical standards to assess its accuracy and precision. The values obtained for standard rocks agree with the literature values. At the 100-ppm level, the analytical precision for chlorine is within ±5% (2σ).     

Determination of Cr, Ni, Cu, Zn and Cd in niobium by radiochemical proton-activation analysis

A rapid radiochemical proton-activation technique based on the utilization of short-lived indicator radionuclides (t(1/2) = 7-100 min) for the determination of Cr, Ni, Cu, Zn, and Cd in niobium is described. It involves the irradiation of the samples with 13-MeV protons, the post-irradiation decontamination of the sample surface, a rapid sample dissolution, a separation procedure based on anion-exchange from HF medium, and counting the eluate with a high-resolution gamma-spectrometer. In addition, for the determination of Ni, a specific separation procedure is proposed. For a 20-min ir-radiation with a beam intensity of 10 microA and a delay time of 20 min, the limits of detection are 4 ng/g for Cr, 0.5 ng/g for Ni, 60 ng/g for Cu, 0.5 microg/g for Zn and 0.2 microg/g for Cd. For Cr, Ni, and Cu, the results obtained by this technique are compared with data obtained by radiochemical neutron-activation analysis and atomic-absorption spectrometry.     

Determination of Macro, Micro and Ultra Micro Concentration of Some Elements in Normal and Diseased Tissues of the Bone by NAA Employing 252Cf and Reactor Neutrons

A method has been developed for the determination of elements in normal and diseased tissues of the bone employing radiochemical and instrumental neutron activation analysis. Elements such as Na, Br, Au, Sb, Sc, Fe, Zn and Cr were subjected to irradiation in ²⁵²Cf or CIRUS reactor followed by measurement of the activity on a HPGe detector coupled to a PC based MCA unit. Elements such as Co, Ca and P were subjected to radiochemical separation prior to the measurement. The statistical evaluation with respect to accuracy and precision is discussed.     

Activation analysis of platinum in gold via199Au

Platinum is determined in gold by activation analysis by means of¹⁹⁹Au after separation of the matrix at the end of irradiation before the daughter nuclide forms. The method involves the radiochemical separation of gold by chloro-complex extraction with MIBK from 1N HCl, and energy-selective pulse counting of¹⁹⁹Au at 158 keV. The irradiation problems are presented. The dependence of the extractability of the gold chloro-complexes on the acidity and the type of solvent are investigated. The procedure of analysis is described. The results obtained in determining 5–700 ppm Pt in Au, Pd and Rh are discussed.     

Determination of total mercury in environmental and biological samples using k0-INAA, RNAA and CVAAS/AFS techniques: Advantages and disadvantages

The accuracy and precision of the results obtained for total mercury in various environmental and biological samples and certified reference materials (CRMs) by various analytical methods, including k ₀-instrumental neutron activation analysis (k ₀-INAA), radiochemical neutron activation analysis (RNAA) and cold vapour atomic absorption (and atomic fluorescence) spectrometry (CVAAS/AFS) used in routine analysis in our laboratory, were investigated. Three natural matrix reference materials (RMs) from the International Atomic Energy Agency (IAEA), five CRMs from the Institute for Reference Materials and Measurements (IRMM), six CRMs from the National Institute of Standards and Technology (NIST) and one from the Jožef Stefan Institute (IJS) were analyzed. The results obtained show good agreement between certified or assigned values, and between the methods used, except for some data obtained by k ₀-INAA in biological samples. This can be explained by losses during irradiation in semi-open systems (irradiation in plastic ampoules) and/or spectral interferences. This revised version was published online in August 2006 with corrections to the Cover Date.