Determination of metals in alloys by neutron capture gamma-ray spectrometry

A collimated neutron beam capable of providing a thermal neutron flux of 4.75·10⁷ n·cm⁻²·sec⁻¹ has been used to analyze alloy samples of 1–5 g during relatively short irradiation times of 30 min by the use of neutron capture gamma-ray spectrometry. The analyses were performed by using a mathematical treatment that relates the count ratio of every constituent present in the matrix with the concentration and thus it requires no standards. The technique was applied to the analysis of steel and gold alloy samples. Errors ranged from 0.8%–10%.     

Rare-earth elemental analysis of banded iron-formations by instrumental neutron activation analysis

Representative banded iron-formations (BIFs) from various locations of the eastern Indian geological belt were investigated by instrumental neutron activation analysis (INAA). After pre-concentration, irradiation was carried out using a neutron flux of 5.1·10¹⁶ m⁻²·s⁻¹, 1.0·10¹⁵ m⁻²·s⁻¹ and 3.7·10¹⁵ m⁻²s⁻¹, with thermal, epi-thermal and fast neutrons, respectively. The activities in these samples were measured by a HPGe detector. Ten rare-earth elements, such as La, Ce, Nd, Sm, Eu, Tb, Ho, Tm, Yb and Lu, have been qualitatively identified and quantitatively estimated in these samples. The present investigation is an example of employing a pre-concentration method for high iron-containing ores prior to neutron activation analysis.     

Test-fitting on adsorption isotherms of organic pollutants from waste waters on activated carbon

An alternative method of approach has been developed for the measurement of thermal neutron flux. The method depends only on the activity of the bare foil if the cadmium ratio at the irradiation position is known. The method has been tested on the GHARR-1 facility at the Ghana Atomic Energy Commission using gold and indium foils for the measurement of the thermal neutron flux in the flux range of 10¹⁰–10¹² n·cm⁻²·s⁻¹ and the results compare very well with those obtained using the conventional method (cadmium separation method).     

Determination of nanogram quantities of gold in biological tissues by nondestructive neutron activation analysis

We describe a method for gold analysis in kidney and liver. The technique is simpler than other methods in that it does not require ashing or acid digestion of the sample. The tissue is dried, placed into a polyethylene vial and diluted with a 2 ml sodium chloride solution. Gold concentration is determined by neutron activation analysis. Samples are irradiated for two hours at a thermal neutron flux of 10¹²n·cm⁻²·s⁻¹ and are then allowed to decay for 3–4 days before counting. The detection limit (20 ng Au/ml) and precision (±6.1%) permits the accurate analysis of gold in these tissues. This technique could aid in a re-examination of gold metabolism.     

Halogen speciation in the rat thyroid: Simultaneous determination of bromine and iodine by short-term INAA

The study describes a mode of non-destructive simultaneous determination of bromine and iodine concentrations, by reactor instrumental neutron activation analysis (INAA) in the regime of short-term activation. Under the conditions of 1-minute activation in the neutron flux of 8.0·10¹³ n·cm⁻²·s⁻¹, it was possible to determine reliably as little as 5·10⁻⁸ g bromine and about 10⁻⁷ g iodine in matrices of a given type and of the mass of about 5 mg dry weight. We applied this method for the determination of Br and I concentrations in the whole rat thyroid gland as well as for the halogen speciation in fractions separated from this organ.     

Instrumental activation analysis for determining the composition of micro-ingots of multi-constituent alloys

A procedure for the instrumental neutron activation analysis of micro-ingots of alloys containing In, Sb, Au, Ga, Ni, Sn and Bi is proposed. The non-destructive analysis of the irradiated samples is performed by γ-spectrometry techniques including one-crystal scintillation detectors, dual-crystal sum-coincidence scintillation detectors and Ge(Li) semiconductor detectors. As a result, the cumbersome operations of radiochemical separation can be eliminated. The sensitivity of quantitative determinations using scintillation detectors in alloys of the above composition is 10⁻¹⁰ g for indium, gold, antimony and gallium and 10⁻⁶ g for nickel and tin. The use of semiconductor detectors yields sensitivities of 10⁻¹⁰ g for indium and gold and 10⁻⁹ g for gallium and antimony.     

Neutron activation analysis of rare earth impurities in metallic uranium

A method with a sensitivity of 2·10⁻⁷ to 1·10⁻¹⁰% has been developed for determining Yb, Ho, Dy, Gd, Eu, Sm and La impurities in metallic uranium by means of neutron activation. The method is based on a preliminary chromatographic separation of the total amount of rare earth elements from uranium by passing the solution in sulphuric acid through KU-2 cation exchange resin and eluting the traces of uranium retained by the resin with a solution of ascorbic acid. The rare earth impurities are then eluted from the resin with 4–5N HCl, evaporated, and irradiated for 20 hours with a neutron flux of 1.2·10¹³ n·cm⁻²·sec⁻¹. Subsequently the traces of the rare earth elements are co-precipitated with Fe(OH)₃, dissolved in concentrated HCl and separated from the iron and other impurities by passing the solution through Dowex 1X8 anion exchange resin in the chloride form. The individual rare earth elements are then separated from each other using KU-2 cation exchange resin and a solution of ammonium α-hydroxyisobutyrate as the eluant.     

High precision instrumental neutron activation analysis of Sn in cassiterite with the aid of an227Ac−Be isotopic neutron source

A non-destructive method has been developed for the precise and accurate determination of Sn in cassiterite ores. Irradiation is performed by means of a 6.6 Ci²²⁷Ac−BE isotopic neutron source with a total neutron output of 10⁸ n·sec⁻¹. Samples are pellets pressed from a mixture of cassiterite powder and wax as a binding material. With a 4 hrs analysis time and a relative precision of 0.45%, the new method is faster and at least as precise as any existing destructive chemical method. The accuracy is proved to be better than that of the commonly used iodimetric titration method.     

Determination of natural uranium in biological samples using the solid state nuclear track detector method

For the solution of most of the problems which are connected to the biological and physiological role of natural uranium in plants and animal organisms about 10⁻¹⁴ g uranium should be determined. However most of the physico-chemical methods for the determination of natural uranium in biomaterials are time-consuming and possess considerable error. On the basis of addition and inner standard methods a version of Solid State Nuclear Track Detectors (SSNTD) method has been developed in order to determine the natural uranium in biospecimens. According to the experimental data simple relations have been obtained for the calculation of uranium concentration in biomaterial and minium uranium concentration in biosolution which can be measured by the detector used. Under irradiation of SSNTD at a thermal neutron flux of (3–5)·10¹⁵n·cm⁻² the detector sensitivity is 2.30·10⁻⁹ g U/ml for glass detectors; 9.60·10⁻¹⁰g U/ml for the detectors made from artificial mica.     

Multi-element analysis of biological samples after intense neutron irradiation an fast chemical separation

For the simultaneous determination of many elements in small biological samples, a multi-element analysis has been developed using neutron activation. After a 24-hr irradiation in a neutron flux of 2.5·10¹⁴ n·cm⁻²·sec⁻¹ and after immediate chemical separation without cooling, it was possible to analyse 24 elements in bovine liver (NBS-SRM 1577). The separation apparatus, set up in a shielded cell can work four samples simultaneously, and its operation is fast enough to allow the detection of radioisotopes with a half-life of about 2 hrs (¹⁶⁵Dy,^57mSr,⁵⁶Mn). Amounts lower than 10⁻³ μg of Dy, Eu, Pr, Sm and Yb were determined.     

Interference by neutron induced second order nuclear reaction in activation analysis of rare earths

In determining the trace impurities existing in high-purity rare earth samples by the neutron activation analysis, there are much interference due to nuclides induced from neutron induced second order nuclear reaction. This paper presents the degree of interference calculated over the ranges of irradiation time from 10⁵ to 10⁷ sec and of thermal-neutron flux from 1·10¹² to 1·10¹⁵ n·cm⁻²·sec⁻¹. According to the results of these calculations, degree of interference under the neutron irradiation condition for 288 hrs in the thermal-neutron flux of 3·10¹³n·cm⁻²·sec⁻¹ is concluded to be 6.4·10⁶ ppm Gd in Eu, 2.2·10⁴ ppm Sm in Eu, 1.9·10⁴ ppm Ho in Dy, 1.1·10³ ppm Eu in Sm, 1.1·10² ppm Ce in La and 1.1·10 ppm Tb in Gd, respectively. Especially, the Gd determination in the Eu target is extremely affected by¹⁵³Gd formed from the¹⁵¹Eu (n, γ) reaction. On the contrary, this reaction is effective in producing¹⁵³Gd activity.     

Ultra-sensitive determination of K, Th, U and other trace impurities in liquid organic scintillators by NAA

We present a NAA method to determine ultratraces of K, Th, U and other trace impurities in liquid organic scintillators, which are known as ultrapure detector materials for neutrino or dark matter experiments. A combined optimization of relevant factors for sensitive NAA has been realized, leading to a sensitivity for U down to 10⁻¹⁶g/g. Samples of 250 ml have been irradiated up to 120 h at a thermal neutron flux of 5–8·10¹²·n·cm⁻²·s⁻¹. Acidic extraction, wet ashing and TBP-extraction are used for radiochemical separations. Finally, coincidence techniques are applied for increased sensitivity.     

Fast-neutron activation analysis with short-lived nuclides

At the GKSS Research Center Geesthacht, a new 14 MeV activation facility—a 5·10¹² n/s neutron generator combined with a fast rabbit system (KORONA)—is being installed. Homogeneous neutron flux at a level of 5·10¹⁰ n·cm⁻²·s⁻¹ and sample transfer times of 140 ms to a 16m distant detector station are characteristic features of the facility described in the paper. With special consideration of short-lived nuclides and including cyclic activation, the analytical prospects with the intense neutron source are discussed, and sensitivities for 78 elements are presented.     

Neutron activation analysis of uranium in human bone,drinking water and daily diet

Uranium in human bone, drinking water and daily diet has been determined by neutron activation analysis using the²³⁸U(n, γ)²³⁹U reaction. An improved scheme for the separation of the²³⁹U is proposed; with this scheme, after neutron irradiation in a 100 kW TRIGA reactor, a uranium content as low as 5·10⁻¹¹ g can be determined reliably, rapidly and easily. A wide range of uranium concentrations, from about 0.1 ppb up to about 10 ppb has been found in the bones of normal Japanese. Water from several Japanese city water services, and the daily diet taken in two Japanese cities, have been found to contain an average 9·10⁻⁹ g/l and 1.5 μg per person-day uranium, respectively.     

The search for internal isotopic tracers in metallurgical materials

In a search for internal isotopic tracers in metallurgical materials a group of elements has been chosen which can be determined by the neutron activation method with the higher sensitivity. A method has been developed for the determination of W, As, Au, La, In, Sc, Re and Ir in metallurgical materials. The separation of the elements was carried out using extraction and precipitation. The determination of the elements was carried out in samples of chamotte brick and washed ores. The limits of the determination of the elements are of the order of 10⁻¹¹ g for Au, 10⁻¹⁰ g for In and La and 10⁻⁹ g for As, W, Sc, Re and Ir. The large scatter of the results indicates the inhomogeneity of the materials analyzed.     

Reagent-loaded and unloaded polyurethane foam as preconcentration matrix in neutron activation analysis

Loaded and unloaded polyurethane foams were examined as a preconcentration matrix in combination with neutron activation analysis. The structure of the foamed polymer is not damaged by short irradiation periods. However the foam skeleton degraded after irradiations for one hour or longer in a neutron flux of 3·10¹³ n ·cm⁻²·s⁻¹. The presence of tin as a major impurity in the polyether-type foam has been detected. This may affect the sensitivity of determination of the relatively short lived isotopes of the elements collected on the foam. On the other hand the polyester-type foam was found to contain only very low amounts of tin. Antimony, indium, gold and mercury collected on the foams were determined with reasonable accuracy.     

The estimation of barium in biological material by neutron activation analysis

Barium is estimated in biological material by thermal neutron activation analysis and measurement of¹³⁹Ba by γ-counting. The biological material is digested with nitric acid and scavenged with ferric hydroxide. A special fluoride precipitation removes calcium and strontium and the barium is recovered as the chromate. The method allows the analysis of up to 40 samples per day and the sensitivity is 0.1 μg after irradiation for 85 mins at 4·10¹²n·cm⁻²·sec⁻¹.     

Detection limits of Au using fast and thermal neutron activation analyses

The applicability of fast and thermal neutron activation analyses for the determination of gold in rock samples has been studied. Using a Ge/Li/ detector limit of 0.45 mg g⁻¹ was obtained for a fast neutron flux of 8.10⁷ n cm⁻².s⁻¹. With a thermal neutron flux of 6.10⁵ n cm⁻².s⁻¹ and the same detector a value of 35 μg g⁻¹ was obtained. Using a NaI/Tl/ crystal a sensitivity of 14 μg g⁻¹ was attained at the same thermal flux. This work was supported in part by the Hungarian Academy of Sciences.     

Fabrication de128Xe comme traceur pour l'analyse de traces de xenon

¹²⁸Xe is produced by one-day irradiation of potassium iodide at a neutron flux of 10¹³ n·cm⁻²·s⁻¹ at a rate of 0.9 mm³ TPN for one gram of iodine. Xe is separated from the matrix by melting or hydrolysis. The main part of water is removed from the gas by cooling. Xenon (∼99%) thus obtained is freed from H₂, O₂, N₂, CH₄ and the last traces of water by gas chromatography and used for isotopic analysis.