Lower limit of determination values for trace elements in iron certified reference materials by neutron activation analysis with multiple gamma-ray detection

Recycling steel products demands a new technique for determining tramp elements in steel. Tramp elements, As and Sb, in some iron certified reference materials were determined by neutron activation analysis with multiple gamma-ray detection method and reported in MTAA11. In MTAA12, the authors reported the lower limit of determination values (LDL) and the dispersion of this method. The values of the LDLs for As and Sb in high purity iron were 0.002 and 0.0009 μg·g⁻¹. The dispersion is small enough to satisfy the demand from materials science.     

Determination of iron isotopes by neutron activation analysis

Instrumental neutron activation analysis has been applied to the determination of Fe isotopic abundances in iron materials with the experimental accuracy of 5%. The proposed method can be considered as a quite simple and fast quality check system on the iron isotope enriched oxides used as standard in Mössbauer spectroscopy.     

Determination of boron in materials by cold neutron prompt gamma-ray activation analysis

An instrument for cold neutron prompt gamma-ray activation analysis (PGAA), located at the NIST Center for Neutron Research (NCNR), has proven useful for the measurement of boron in a variety of materials. Neutrons, moderated by passage through liquid hydrogen at 20 K, pass through a (58)Ni coated guide to the PGAA station in the cold neutron guide hall of the NCNR. The thermal equivalent neutron fluence rate at the sample position is 9 x 10(8) cm(-2) s(-1). Prompt gamma rays are measured by a cadmium- and lead-shielded high-purity germanium detector. The instrument has been used to measure boron mass fractions in minerals, in NIST SRM 2175 (Refractory Alloy MP-35-N) for certification of boron, and most recently in semiconductor-grade silicon. The limit of detection for boron in many materials is <10 ng g(-1).     

Determination of boron in borosilicate glasses by neutron capture prompt gamma-ray activation analysis

Major levels of boron in borosilicate glasses have been determined nondestructively by neutron activation analysis. In contrast to chemical methods for determining boron as a major component, the described nuclear method has few interferences and does not require chemical separation of boron prior to its quantitation. The effects of neutron self-shielding by boron (1 to 8% by weight) are examined, minimized by dilution of powdered samples with high purity graphite, and circumvented by comparative analyses. Results of the analysis of a series of glasses with increasing boron composition are 1.150±.005% and 7.766±.035% for the low and high members of the series. Accuracy of these results depends upon comparative analyses with the certified Standard Reference Material, SRM 93a (3.89±0.02% B). Once analyzed, the glasses are useful as secondary standards for alpha track counting, and also ion and electron microprobe analyses of glasses.     

Determination of 32 elements in rocks by neutron activation analysis and high resolution gamma-ray spectroscopy

Neutron activation analysis and Ge(Li) spectroscopy was used to determine 32 elements in seven U.S.G.S. standard rocks of a wide range of composition. Short half-life nuclides (10 sec-10 min) were used to measure Sc, Hf, Dy, Mg, Al, Ca, Ti, V (and Na) in an automated rabbit Ge(Li) detector system. The elements K, Cu, Zn, Ga, Sr, Ba, La, Eu, Sm (and Mn) were determined by dissolution of the irradiated sample followed by removal of²⁴Na on hydrated antimony pentoxide (HAP). Long-lived nuclides were used to measure Sc, Cr, Fe, Co, Zr, Rb, Sb, Cs, Ba, Ce, Eu, Yb, Tb, Lu, Hf, Ta and Th after decay of²⁴Na. The method involves little radiochemistry and the separation is selective for²⁴Na under the experimental conditions used. Elemental concentrations determined agree well with previously published data.     

In-beam neutron activation analysis of stainless steel and iron ore

Pulse radiolysis of MIT and DIT irradiated to doses from 2.8·10⁴ to 85·10⁴ rads is studied by ascending chromatography. The 3-iodo-4,5-dihydroxyphenylalanine (DOPA-I) and 3-iodo-4-hydroxyphenylalanine have been identified as first stages of degradations of MIT and DIT, respectively. G values are 0.015 for MIT (10⁻⁵M) and 0.004 for DIT (0.5·10⁻⁵M). By self decomposition MIT is degraded less rapidly than DIT and there is no formation of DOPA-I.      

High precision instrumental neutron activation analysis of uranium by multiple gamma-ray peak ratio determination

The method of multiple γ-ray peak ratio determination has been applied to the nondestructive neutron activation analysis of uranium in rocks and ores. The photopeaks of²³⁹Np gamma-rays produced by the activation of²³⁸U and those of the fission products of²³⁵U are a measure of the quantity of uranium in the irradiated sample, provided that the uranium is of natural isotopic composition. The ratios between the integrated areas of the different photopeaks are calculated and compared with those obtained for a uranium standard. The uranium concentration in the sample is calculated from the photopeaks whose ratios correspond, within the error limits to those of pure natural uranium. High accuracy better than ±2% has been obtained.     

Prompt gamma-ray neutron activation analysis by the absolute method

In this study an investigation into the applicability of the absolute method in Prompt Gamma-ray Neutron Activation Analysis (PGNAA) was undertaken. Although the system parameters are adequately characterized, the scatter in nuclear data for a number of elements is significant. For our particular experimental set up the K-factors were calculated for a number of elements using both Au and Fe as monostandards. A comparison was made between the calculated and experimentally determined K-factors and from this comparison the feasibility of the absolute method in neutron prompt gamma-rays can be realized for a number of elements.     

Determination of silicon in iron by thermal neutron activation

A new chemical separation procedure for the determination of silicon in iron after neutron activation was developed. It uses two separation steps, one on a cation exchange resin in HCl−HF-acetone medium, and the other on alumina at pH 9. The detection limit for silicon was 0.02 μg. This analytical procedure was applied to the control of the zone-melting purification of iron.     

Determination of selenium in foods by pseudo-cyclic neutron activation and anti-coincidence gamma-ray spectrometry

A pseudo-cyclic instrumental neutron activation analysis method in conjunction with anti-coincidence gamma-ray spectrometry (PC-INAA-AC) has been developed for the determination of ppb levels of Se. The method consists of repetitions of the irradiation-decay-counting cycles of a sample using the rapid transfer cyclic system at the Dalhousie University SLOWPOKE-2 reactor facility. The 162-keV γ-ray of ^77mSe (t _1/2 = 17.4 s) has been found to be highly selective. The precision and detection limits are significantly improved and the total experimental time drastically reduced by this method. Detection limits are between 2 and 9 ng. The accuracy of the method has been evaluated by analyzing a number of nutritional reference materials. The PC-INAA-AC method has been applied for the routine determination of Se to the composites of 135 food samples with values ranging from as low as 1 ng g⁻¹ for tea to 1,045 ng g⁻¹ for organ meats on fresh weight basis.     

Elemental analysis by gamma-ray detection following inelastic neutron scattering

A method of elemental analysis based on the detection of prompt γ-rays produced by the inelastic scattering of fast monoenergetic neutrons has been investigated. Time-of-flight discrimination techniques and the use of Ge(Li) detectors provide significant advances over previous studies. This method is multielemental, non-destructive, and essentially free of interferences and matrix effects. Sample analysis is rapid and selective excitation of various elements is possible. Many elements have been examined by this technique and minimum detection limits have been established. This method has been applied to the analysis of metal alloys.     

Determination of silicon dioxide in iron and steel-making slags and fluorspars by 14 MeV neutron activation and high-resolution gamma-ray spectrometry

Silicon as silicon dioxide in iron and steel-making slags and fluorspars was analyzed by 14 MeV neutron activation high-resolution γ-ray spectrometry. Silicon was detected by measuring the 1.78 MeV γ-ray of²⁸Al, the product of the²⁸Si(n, p) reaction, using a 30 cm³ coaxial Ge(Li) detector. A modified TPA method was used for the calculation.²⁸Al is also produced from phosphorus by the³¹P(n,α) reaction, and from aluminium by the²⁷Al(n,γ) reaction. The contribution from the former reaction could be corrected experimentally when the P₂O₅ content of the sample was known, while the latter reaction could be neglected in this neutron energy region. The experimental correction coefficient for phosphorus agreed well with the theoretical value calculated from the nuclear properties of silicon and phosphorus. Yields of²⁸Al from SiO₂, P₂O₅ and Al₂O₃ of the same weight percentages were calculated as 1, 0.426 (experimentally 0.44) and 0.0022, respectively. The results of this method agreed well with the results of the usual chemical methods. The limit of detection of SiO₂ in iron and steel-making slags and fluorspars was calculated as 0.07%. The coefficient of variation of repeated experiments was compared with the statistical one.     

Determination of silicon,phosphorus and sulfur in alloy steel by neutron activation analysis

Silicon, phosphorus, and sulfur in alloy steel were determined by neutron activation analysis involving rapid radiochemical separation procedures. The standard deviations for silicon, phosphorus, and sulfur were 1.6%, 2.3%, and 2.4% respectively; the sensitivity limits were 3.2, 0.20, and 2.50 p.p.m., respectively. The three constituents could be determined in alloy steel within 2 h of the irradiation.     

Measurements of Ir concentration in geological standard samples using neutron activation analysis with multiple gamma-ray coincidence method

In this study, the Ir concentrations in some standard rock samples were determined by using the multiple γ-ray detection method. The use of the multiple γ-ray detection method, which was developed for nuclide quantification, yielded better resolution and sensitivity than the ordinary singles γ-ray detection method. Iridium is one of the least abundant elements in Earth’s crust, with an average mass fraction of 0.001 ppm in a crust rock. However, iridium is relatively more abundant (concentration: 0.5 ppm or more) in undifferentiated meteorites. Therefore iridium abundance anomalies in geological samples provide important information about meteorite impact. The standard rock samples used in this study were SARM-76, FC-1 and FC-2. The SARM-76 was prepared from a platinum ore, and issued by the south African bureau of standards. FC-1 and FC-2 were obtained from fish clay sediment samples from Stevens Klint, Denmark.     

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 As,Cd, Cu,Hg, Mo,Sb, and Se in biological reference materials by radiochemical neutron activation analysis

The elements As, Cd, Cu, Hg, Mo, Sb, and Se were determined in the biological reference materials (RMs) Bowen's Kale, NIST SRM-1577 Bovine Liver, NIST SRM-1549 Milk Powder, and Versieck's 2nd Generation Biological RM Human Serum using two newly developed radiochemical neutron activation analysis (RNAA) procedures. The first is based on sample decomposition in a mixutre of H₂SO₄+HNO₃+H₂O₂ and simultaneous extraction of the elements As, Cd–In, Cu, Mo, and Sb by 0.025M Zn(DDC)₂ in chloroform from 2–4M H₂SO₄ in the presence of 0.01M KI. The second consists of sample decomposition in HNO₃ in teflon bombs heated at 150°C, Hg extraction by 0.01M Ni(DDC)₂ in chloroform from about 1M HNO₃, and Se precipitation by ascorbic acid from about 1M HClO₄. The RNAA procedures were also used for intercomparison analyses of A and P NIST Leaf Materials (NIST candidate SRM-1515 Apple Leaves and NIST SRM-1547 Peach Leaves, respectively), and CZIM Bovine Liver 12-02-01 RM. Very good agreement of results with certified and/or literature values proved the high accuracy of these determinations by the proposed RNAA procedures, even at the sub-ng/g levels.     

Determination of silicon in cast iron by 14 MeV neutron activation

Silicon in cast iron was analyzed by 14 MeV neutron activation—high-resolution γ-ray spectrometry. Silicon was detected as²⁸Al, the product of the²⁸Si(n, p)²⁸Al reaction. Interference of⁵⁶Mn was separated using a Ge(Li) detector and a biased amplifying system. The 1. 81 MeV gamma-radiation of⁵⁶Mn, which is the product of the⁵⁶Fe(n, p)⁵⁶Mn reaction of the matrix of cast iron, was used as an internal standard and for correction of the self-absorption of the 1. 78 MeV gamma-radiation of²⁸Al by the sample. The interferences of aluminum, phosphorus and manganese could be neglected according to the results calculated from their nuclear properties and contents in the cast iron of this experiment. The results of this method agreed well with the results of the usual chemical method, with errors less than 5% of the results, and the precision of the method was satisfactory with a C. V. of less than almost 6% for rapid analysis of silicon in cast iron. The analytical line through the origin with a slope of the mean value of the repetition experiments could be used as the analytical line with almost the same precision and accuracy of the results as for the analytical line calculated by the least squares method.