Non-destructive determination of silicon in aluminium-silicon alloys by neutron activation analysis with a 227Ac-Be isotope neutron source

A method has been developed for the accurate determination of silicon in binary Al-Si alloys by instrumental neutron activation analysis with the aid of an ²²⁷Ac-Be isotope neutron source. Discs, weighing ca. 4 g, are irradiated at the maximum of the fast flux gradient in a rabbit lined internally with two layers of cadmium foil. Each irradiation is followed by an integral mode counting with discriminator baseline setting at 1400 keV. Standards consist of discs from high purity semiconductor silicon and aluminium (99.99%) metal. An iterative calculation procedure yields results with a relative precision from 0.6 to 8.1% for silicon contents between 13.5 and 0.5%. Triplicate analysis requires 21 min.     

Determination of silicon in aluminium by 14 MeV neutron activation analysis

A method has been developed for determining silicon in aluminium by fast neutron activation. It is based on the separation of two gamma lines by a Ge(Li) detector: the 1.73 MeV line from the product of²⁷Al(n, α)²⁴Na and the 1.78 MeV line from the²⁸Si(n, p)²⁸Al reaction. In the case of aluminium-silicon alloys 100 μg silicon can be determined, with an error of 10% in an aluminium sample of 1 g. This work was supported in part by the International Atomic Energy Agency.     

The determination of silicon in steel by 14-mev neutron activation analysis

A fast (2–5 min) non-destructive determination of silicon in steel by 14-MeV neutron activation is described. The 1.78-MeV ²⁸Al activity, induced by the reaction ²⁸Si(n,p)²⁸Al, is counted on a NaI(Tl) detector. An oxygen flux monitor is used to normalise to the same neutron flux.Two methods are described to correct for the ⁵⁶Mn activity (2.58 h), induced into the iron matrix via ⁵⁶Fe(n,p)⁵⁶Mn. Nuclear interferences of phosphorus and aluminium have been examined. Special attention has been paid to stainless steels. A sensitivity of 0.02 to 0.05% of silicon is obtained. The precision is 2 to 3% for steels containing above 1% silicon, and 7% for 0.1% of silicon.     

Instrumental neutron activation analysis applied to the determination of the chemical composition of metallic materials with study of interferences

Summary Instrumental neutron activation analysis was applied to evaluate the chemical composition of metallic materials, namely iron, steel, silicon and ferrosilicon certified reference materials. As, Co, Cr, Mn, Mo, Ni, V and W concentrations were analyzed in the iron and steel samples whereas 21 elements were determined in silicon and ferrosilicon samples. Accuracy and precision results of about 10% were achieved for most elements, indicating that the technique is suitable for the analysis of metallic materials. Interferences of Cr and Mn in V; Fe and Co in Mn; Co in Fe and Cr in Ti were quantified and only the last one was critical to the analysis of the materials employed in this work.     

Method for determination of silicon in plant materials by neutron activation analysis

Silicon has been found to be an essential element for the growth and development of many ecomomically important plants such as sugarcane, rice, oats, and wheat. A method is described for the quantitative determination of silicon in plant samples. Measurements were made with two Ge(Li) detectors matched with a multiplexing unit to provide a single amplified signal to a computerized analyzer system. For those materials containing greater than 0.5 weight percent silicon, the reaction²⁹Si(n, p)²⁹Al (1273 keV) provides a direct measurement of the quantity of silicon provided the irradiation is done in a special boron nitride capsule to reduce interferences from thermal neutron reactions and a correction is made for the single escape line from²⁸Al (1268 keV). For lesser quantities of silicon, a technique which utilizes the fast neutron reaction²⁸Si(n, p)²⁸Al is preferred. Corrections for the interference produced by the presence of phosphorus³¹P(n, α)²⁸Al are made by determining the phosphorus content following the instrumental analysis using a unique application of neutron activation analysis, i. e., measurement of tungsten in tungstomolybdophosphoric acid produced when molybdate and tungstate ions are added to dissolved samples of the plant material containing phosphorus. Aluminum, which may also produce an interference by thermal neutron reaction²⁷Al(n, γ)²⁸Al, is determined directly from the original activation data after subtracting out the effect of the phosphorus. Thus, three irradiations in the pneumatic sample irradiator are necessary; one short irradiation (1 min) without thermal neutron shielding, a longer irradiation (6 min) in the boron capsule, and a final irradiation of the tungstomolybdophosphoric acid provide all data required to accurately determine silicon in plant materials. A computer program has been developed that provides rapid reduction of the data in final report format. Elements such as sodium, chlorine, calcium, manganese, potassium, and magnesium extrinsic to the analysis for silicon are also determined by this method. The method has been tested on a large number of samples and reliable results are obtained with less than 0.2 g of sample. This work was supported by Grant 533 from the Michigan Memorial—Phoenix Project.     

Non-destructive determination of silver in lead by neutron activation with a 227Ac-Be isotopic neutron source

A method has been developed for the determination of silver in lead by instrumental neutron activation analysis with the aid of a ²²⁷Ac-Be isotopic neutron source. The samples are irradiated for 60 s, allowed to decay for 10 s, and counted for 60 s. ¹¹⁰Ag can be measured free of interferences provided that copper and antimony do not occur in concentrations higher than ca. 1000 p.p.m. A calibration curve was established for silver concentrations between 0 and 4000 p.p.m. by means of standards prepared by melting together high-purity silver and lead under a hydrogen atmosphere. For 17.5-g lead samples, containing between 1000 and 2500 p.p.m. of silver, a mean relative precision of 0.8% was obtained after a 10-min analysis.     

Determination of cadmium in zinc ores by thermal neutron absorption analysis

A method has been developed for routine determination of cadmium in zinc ores by thermal neutron absorption analysis, based on the attenuation of a thermal neutron flux passing through a neutron absorbing material. The thermal neutron flux is related to the⁵²V-activity induced in a vanadium detector, surrounded by pellets pressed from a mixture of powdered material with graphite. Besides cadmium, also the major constitutents zinc, iron and sulfur contribute significantly to the total attenuation of the thermal neutron flux. Calibration lines for these elements are worked out. All irradiations are carried out for 200 s in the partially thermalized neutron flux of a 5 Ci²²⁷Ac—Be isotope neutron source. After a decay of 30 s, the⁵²V-activity of the vanadium detector is measured for 400 s with a NaI(T1) scintillation detector. The analysis sequence, including the computation of the results from the counting data, is automated by means of a LSI—11 microprocessor with 12K×16 bit memory. Zinc ores, containing 0.02 to 1.45% cadmium, have been analyzed with a precision ranging from 12.6% to 0.54% relative. As a test for the reliability of the method, two NBS standard reference materials were analyzed in the same way as the zinc ore samples.     

Estimation of sulfur in coal by fast neutron activation

A simple method is described for estimation of sulfur in coal using fast neutron activation of sulfur, i.e.³²S(n,p)³²P and subsequent measurement of³²P -activity (1.72 MeV) by a Geiger-Müller counter. Since the sulfur content of Indian coal ranges from 0.25 to 3%, simulated samples of coal containing sulfur in the range from 0.25 to 3% and common impurities like oxides of aluminium, calcium, iron and silicon have been used to establish the method.     

Direct determination of silicon in powdered aluminium oxide by use of slurry sampling with in situ fusion graphite-furnace atomic-absorption spectrometry

A direct method for determination of silicon in powdered high-purity aluminium oxide samples, by slurry sampling with in situ fusion graphite-furnace atomic-absorption spectrometry (GF-AAS), has been established. A slurry sample was prepared by 10-min ultrasonication of a powdered sample in an aqueous solution containing both sodium carbonate and boric acid as a mixed flux. An appropriate portion of the slurry was introduced into a pyrolytic graphite furnace equipped with a platform. Silicon compounds to be determined and aluminium oxide were fused by the in situ fusion process with the flux in the furnace under optimized heating conditions, and the silicon absorbance was then measured directly. The calibration curve was prepared by use of a silicon standard solution containing the same concentration of the flux as the slurry sample. The accuracy of the proposed method was confirmed by analysis of certified reference materials. The proposed method gave statistically accurate values at the 95% confidence level. The detection limit was 3.3 μg g^–1 in solid samples, when 300 mg/20 mL slurry was prepared and a 10 μL portion of the slurry was measured. The precision of the determination (RSD for more than four separate determinations) was 14% and 2%, respectively, for levels of 10 and 100 μg g^–1 silicon in aluminium oxide.     

Instrumental neutron activation analysis of silicon wafers using the silicon matrix as the comparator

For the instrumental neutron activation analysis of trace impurities in high purity silicon wafer, a modified single comparator method has been applied. The energy distribution of the neutrons at the irradiation position was measured using the two flux monitors, Au and Co, and elemental contents were calculated using the silicon matrix in the wafer as a comparator. This has advantage of reducing the cross contamination from an external monitor during sample preparation and irradiation, the uncertainties from the non-homogeneity of the neutron flux and the error on the weight of comparators. Determination limits for 49 elements were presented under the condition of 72 hours irradiation at a neutron flux of 3.7·10¹³ n·cm^-2·s^-1 and 4000 s measurement. The analytical results obtained by this method and the conventional single comparator method were compared and were found to agree well within 5%.     

Multielement radiochemical neutron activation analysis of high purity aluminium

Summary A radiochemical neutron activation analysis technique for the determination of 51 elements in high purity aluminium via medium- and long-lived indicator radionuclides has been developed. It is based on a separation procedure involving the removal of ²⁴Na, produced via the reaction ²⁷Al(n,), on a hydrated antimony pentoxide column and further separation of the radionuclide mixture into 11 groups on two Dowex 1X8 columns and one Dowex 50X8 column from HCl/HF and HCl media as well as the extraction of copper with APDTC in chloroform. The indicator radionuclides for the significant impurities thorium and uranium, ²³³Pa and ²³⁹Np, were separated with satisfactory selectivity in one fraction. For 43 elements, the limits of detection are <10 ng/g, for thorium and uranium, they are 50 pg/g. The method was applied to the analysis of different high purity aluminium samples. For a number of elements, the results of this technique are compared with those of other techniques.

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Radiochemische Multielement-Neutronenaktivierungsanalyse von hochreinem Aluminium

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Dedicated to Prof. Dr. W. Fresenius on the occasion of his 75th birthday     

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.     

Substoichiometric determination of Cd by neutron activation analysis

A rapid method has been developed for the determination of cadmium in environmental samples by thermal neutron activation analysis involving substoichiometric extraction with 1,2,3-benzotriazole /1,2,3-BT/. Cd was radiochemically separated as CdS using 1-amidino-2-thiourea. The time required for radiochemical purification containing two samples and a standard was about 2 h. 4.63 g of Cd can be determined with an accuracy of 6.69% and precision of 6.25%. Mash potatoes, animal bones, raw sludge and cattle manure have been analyzed by this method.     

Determination of uranium and thorium at the sub-ng/g-level in high-purity aluminium by radiochemical neutron activation analysis

Summary A radiochemical neutron activation analysis technique for the determination of uranium und thorium in highpurity aluminium via the indicator radionuclides ²³⁹Np and ²³³Pa, respectively, has been developed. The separation procedure is based on the removal of ²⁴Na on hydrated antimony pentoxide followed by ion-exchange on Dowex-1X8 from HCl/HF and HCl medium. The eluate fraction being of interest for the determination of uranium and thorium contains > 99% of ²³⁹Np and ²³³Pa and, in addition, 11±2% of hafnium and 29±5% of zirconium, and non-detectable fractions of other radionuclides. For a 3-day irradiation of a 100 mg sample at a thermal neutron flux of 10¹⁴cm^–2s^–1 and a decay time of 5 days, the attainable detection limit for both elements is 0.05 ng/g. The method was applied to the analysis of different high-purity aluminium samples, and the results are compared with those obtained in other laboratories.

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Bestimmung von Uran und Thorium in hochreinem Aluminium im sub-ng/g-Bereich durch radiochemische Neutronenaktivierungsanalyse

     

The determination of uranium in biological materials by neutron activation analysis using the fission product134I

A method for the determination of uranium based on²³⁵U thermal neutron fission, has been developed and employed on samples of ashed fish tissue and seaweed. The method involves a post-irradiation ion exchange separation of iodine isotopes. The 884 keV photopeak of¹³⁴I is used for measurement. Uranium detection limits in the samples concerned have been estimated to be 1·10⁻⁸g in terms of natural uranium. The precision achieved in analysing several series of 3–5 samples was 4–10 per cent. The accuracy of the method was tested by employing an independent neutron activation procedure based on²³⁹U measurement. The accuracy of both methods was checked by analysing NBS SRM 1571 ‘Orchard Leaves’.     

Determination of boron in water samples by chemical prompt gamma neutron activation analysis

Boron concentration has been determined in groundwater samples, collected from Khuchch, Gujarat, India, by prompt gamma neutron activation analysis (PGNAA) after selective separation and pre-concentration by solvent extraction with 10% 2-ethyl hexane 1,3-diol in CHCl₃. Solvent extraction separation helped to eliminate the interfering elements in PGNAA determination of boron. The sensitivity of PGNAA is found to be 18.83 cps/mg B based on the slope of a calibration plot obtained by carrying out measurements on synthetic boric acid samples containing boron in the range of 30–150 μg. Detection limit of the method is 0.2 μg/g counted for 35,000 seconds at a sample size of 15 gram. The precision (relative standard deviation at 1σ level) and accuracy of the method is 5%. The analytical results of the present method agreed well with well-established spectrophotometric determination of boron as boron-curcumin complex and inductively coupled plasma atomic emission spectroscopy (ICP-AES).     

Determination of bromine and iodine in biological and environmental materials using epithermal neutron activation analysis

Epithermal neutron activation analysis (ENAA) was applied to the determination of the contents of bromine and iodine in 40 biological and environmental standard reference materials and Chinese diets. Boron nitride (BN) for solid samples and BN+Cd for liquid samples were adopted as shield material. Irradiation was carried out in inner and outer irradiation sites in a Miniature Source Reactor (MNSR) for solid and liquid samples, respectively. The 443 keV photopeak of ¹²⁸I and the 616 keV photopeak of ⁸⁰Br were used. The precision of measurement (relative standard deviation) is 2∼6% for contents of iodine of more than 100 ng/g and 8∼12% in the 20∼100 ng/g range in solid samples, and 12∼18% at less than 100 ng/ml in liquid samples. For bromine, the precision of measurement is 2–8% for solid samples and lower than 13% for liquid samples. The detection limits under experimental conditions varied between 10∼30 ng/g, 55∼95 ng/g and 25∼68 ng/g for iodine and 50∼150 ng/g, 200∼450 ng/g and 100∼300 ng/g for bromine in ENAA with BN shield in inner irradiation sites, with Cd shield and BN+Cd shield in outer irradiation sites, respectively. Received: 13 June 1996 / Revised: 2 September 1996 / Accepted: 19 September 1996     

Instrumental neutron activation analysis of gunpowder residues

A procedure has been developed for the detection of gunpowder residues deposited on the hand of a person firing a gun. The method is based on neutron activation analysis of the antimony level on the surface of the hand. The surface materials are removed by a film made by spraying a 4% solution of cellulose acetate in acetone, which sets to form a thin film that can readily be stripped off. This technique was found to be preferable to the paraffin-lift technique which is in common use. Following neutron activation of the film in a nuclear reactor, antimony is assayed by high-resolution Ge(Li) spectrometry without prior chemical processing. The sensitivity of the method is about 5·10⁻⁹ g Sb, with a precision of about ±10% at a neutron flux of 5·10¹³ n·cm⁻²·sec⁻¹. Analysis of twenty samples taken from the hands of persons who had fired a pistol gave Sb levels of 0.4±0.2 μg, compared with 0.024±0.013 μg found on the hands of persons who had not fired a revolver. The possible extension of the present technique to include the determination of additional elements is discussed. Project carried out with the support of the Office of the Chief Scientist to the Ministry of Defense and with the collaboration of the Israel Police.     

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 trace quantities of tin by neutron activation analysis

A neutron activation method of general applicability has been developed for determining traces of tin in a variety of samples. The samples and comparative standards, sealed into ampoules, are irradiated intermittently for 3 days at a neutron flux of ca, 3 · 10¹¹ n/cm²/sec, followed by carrier radiochemical separations mainly consisting of solvent extraction steps. As little as 0.1 μg Sn can be easily determined by comparing the induced β-activity of ¹²¹Sn (27.5 h) with that of a standard, The method is rapid and has a reasonably high chemical yield of about 50%. Results are quoted for the tin contents of a number of materials including silicate rocks, sea waters, biological materials and steels.