Determination of silicon in Japanese iron reference standard materials by reactor fast neutron activation analysis combined with a simple pre-concentration

A reactor fast neutron activation analysis was used in combinationwith a simple pre-concentration procedure for determining silicon in someiron reference standard materials of Japan Iron and Steel Federation. Thesamples were dissolved with aqua regia and digested with perchloric or sulfuricacid. The precipitated silica was collected on a filter paper and irradiatedin a cadmium case with reactor fast neutrons. Silicon can be determined intool steel SKD6, low-alloy steel Nos 2 and 4 and silico-manganese samplesby a present method measuring 1,273.4 keV rays from 6.63-minute ²⁹Alproduced by ²⁹Si(n,p)²⁹ Al reaction.     

Possibilities of low-level determination of silicon in biological materials by activation analysis

The capabilities of neutron and photon activation analysis (NAA and PAA, respectively) for low-level determination of silicon in biological materials have been examined. Sensitivities of a variety of modes of NAA and PAA with radiochemical separation have been evaluated. Results are presented for silicon in reference materials CSRM 12–2-03 Lucerne, Bowen’s Kale, NIST SRM-1571 Orchard Leaves, and NIST SRM-1515 Apple Leaves. The results were obtained by employing the ²⁹Si(n,p)²⁹Al reaction with fast reactor neutrons and the radiochemical procedure developed for aluminium separation. Possibilities of further improvement of the silicon determination limit down to the μg g^–1 level by employing NAA and PAA with radiochemical separation are outlined.     

Aktivierungsanalyse von Silicium in Stahl mit schnellen Neutronen

Three experimentally different methods for analysing silicon in steel by activation with fast neutrons are described. By bombardment of²⁸Si with fast neutrons²⁸Al is obtained after a (n, p) reaction.²⁸Al emits a γ-radiation of 1.78 MeV. The difficulty lies in discriminating the 1.78 MeV peak out of the emitted radiation. The first method consists in determining the ratio of the 1.8 MeV peak to the 2.1 MeV peak of an activated iron sample. From this ratio one can deduct the contribution of²⁸Al to the 1.8 MeV peak of a silicon containing sample. The other method of separation makes use of the different half-lives of the 1.78 MeV γ-rays from²⁸Al and the 1.81 MeV γ-rays from⁵⁶Mn. The direct separation of the peaks with a Ge(Li) detector is the third method. This paper illustrates the possibilities of activation analysis with fast neutrons. For this reason the values measured are compared with the results of chemical analyses.     

Neutron activation analysis of zeolite catalysts

A new method for the determination of aluminum and silicon has been developed for zeolite catalysts. In contrast to previous methods, thermal neutrons are used for the analysis of both elements, and cadmium absorbers are not needed. The silicon determination utilizes a one-hour irradiation to observe the³¹Si produced by the (n, ) reaction of³⁰Si. A 15-second irradiation is used for the²⁷Al(n, )²⁸Al reaction. The²⁸Al activity is corrected for the contribution from the²⁸Si(n,p)²⁸Al reaction by using the analyzed weight of silicon in the sample and the data for a silicon standard irradiated simultaneously with the zeolite and the aluminum standard. The quantitation limits are 0.012 g for silicon and 3.3×10^–5 g for aluminum. Sodium presents a significant interference, but this element can be removed by taking advantage of the ion exchange properties of these materials.     

Non-Destructive Determination of Silicon in Steel and Steel-Related Samples by INAA Using the 29Si(n,p)29Al reaction

A non-destructive method has been developed for the determination of silicon in steel alloys by reactor fast neutron activation analysis using the ²⁹Si(n,p) ²⁹Al reaction. An iron sample and a comparator of pure metallic silicon powder are irradiated in a cadmium case. In order to obtain the net counting rate of the 1273.4 keV peak from ²⁹Al, background activities are corrected carefully to avoid peaks of 1268.0 keV from ²⁸Al single-escape and 1266.2 keV from ³¹Si. The present method is superior to the method using the ²⁸Si(n,p) ²⁸Al reaction.     

Neutron activation analysis of semiconductor silicon

The determination of impurities in semiconductor silicon by nondestructive and destructive NAA is described. To improve the detection limit, a multiple beta—single gamma detector assembly is used. It is shown that²⁴Na is also produced from silicon by a (n, αp) reaction with reactor neutrons. The cross-section with fission neutrons is 1.8·10⁻⁹ barn.     

Errors in activation analysis by nuclear recoil

The recoil energies of up to several MeV developed during nuclear reactions involving particle emission lead to the radionuclides used in the analysis being redistributed between adjacent materials. In aluminum irradiated by reactor neutrons,²⁴Na losses were observed up to a depth of 8·10⁻⁶ m; in the adjacent silicon, a²⁴Na penetration depth was observed up to 4·10⁻⁶ m. Similar results were obtained from reaction products deriving from irradiation of Ti, Ni, N, S and Cl. This means that the results of activation analysis investigations performed for the purpose of evaluating this type of reaction might contain significant errors if thin layers, boundary zones of very small sample volumes are examined. In the analysis of surface layers on silicon devices, completely erroneous results have been obtained in some cases due to the recoil phenomena described.     

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%.     

Performance comparison of 2.8 MeV and <Superscript>241</Superscript>Am-Be neutrons based moisture measurement setups

Performance of a ²⁴¹Am-Be neutron source-based and 2.8 MeV neutrons-based moisture measurement setups have been compared using Monte Carlo simulation. In the setup fast neutrons transmitted through the sample were detected by a fast neutron detector, which was placed behind a massive long double truncated collimator. The setup geometry was optimized to detect maximum effect of 1–7 wt.% moisture on the neutron intensity transmitted through the sample. The yield of neutrons transmitted through concrete, coal, wood and soil samples containing 1–7 wt.% moisture was calculated for 2.8 MeV neutrons and neutrons from an ²⁴¹Am-Be source. The slopes of the fast neutron intensities transmitted through the samples vs. their moisture contents are very sensitive to the neutron energy and the sample composition. Higher slopes have been observed for the samples with larger bulk density. The slopes of fast neutron yield show dependence on the incident neutron energy. Larger slopes have been observed for neutrons with samller energy. Due to the overall large slopes of the transmitted intensity data of the samples for 2.8 MeV neutrons, it is expected to achieve better sensitivity in moisture measurements for a 2.8 MeV neutrons based moisture setup.     

Etude structurale par RMN 29Si—V. Dérivés de la quinoléine et de l'isoquinoléine

A series of silylated compounds obtained from quinoline or isoquinoline were studied by ²⁹Si NMR using the selective polarization transfer (SPT). Both silicon chemical shifts and ²⁹Si, ¹H coupling constants have been measured. These results are the first example of coupling through siliconnitrogen bonds.     

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.     

29Si-NMR-chemische Verschiebung von Verbindungen mit vier elektronegativen Substituenten am Silicium

²⁹Si-NMR Chemical Shift of Compounds with Four Electronegative Substituents at Silicon The influence of the d-orbitals of IIIrd row elements and also the inductive and steric effects of the organoxy groups on the ²⁹Si-NMR chemical shift of compounds with four electronegative substituents attached to silicon wer evaluated. A bridging effect on the transmission of the inductive effects over the oxygen atom which is bonded with silicon was stated.     

40Ar/39Ar — Alter eines Basits der Ostantarktis

The⁴⁰Ar/³⁹Ar technique is an analytical variation of the K–Ar dating method. A known fraction of the³⁹K in a sample is converted to³⁹Ar by irradiation with fast neutrons. In an incremental heating experiment, the argon is released from the sample fractionally by stepwise heating. The result is a series of apparent ages.⁴⁰Ar/³⁹Ar age spectrum was determined for the sample Oase Vestfold. The minimum of the saddle-shaped age spectrum gives 1.0 billion years.     

Characterization of an epithermal irradiation facility

An epithermal energy neutron irradiation facility has been used to perform instrumental activation analysis for iodine, silicon, nickel, zirconium, uranium and thorium. The facility, which is adjacent to the fuel of the University of Virginia 2.0 MW pool reactor, consists of a dry sample region surrounded by a fixed cadmium shield. A boron nitride capsule can be used to hold the sample in the cadmium facility to further enhance the reduction of thermal neutron activation. The neutron fluence rate is 2.2×10¹⁶ n·m^–2·s^–1 for fission spectrum energy neutrons (measured with Ni(n,p)Co) and 8.2·10¹⁵ n·m^–2·s^–1 for resonance energy neutrons (measured with gold).Iodine has been measured at concentrations as low as 0.1 mg/kg with 3% counting statistics in powdered infant formula and 0.15 mg/kg with 5% statistics in liquid infant formula. Silicon has been measured at concentrations of 0.2% in biological samples with counting statistics between 5 and 10% and in coal and soil at concentrations greater than 4% with better than 1% statistics. Nickel has been measured in coal and soil at the 20 mg/kg level and higher with 6% statistics. Zirconium has been determined at 600 mg/kg and greater in ceramics with counting errors less than 3%. Uranium and thorium have been measured at the 10 mg/kg level with 3% counting statistics.     

Radioanalytical prediction of radiative capture in 99Mo production via transmutation adiabatic resonance crossing by cyclotron

In this study, the transmutation adiabatic resonance crossing (TARC) concept was estimated in ⁹⁹Mo radioisotope production via radiative capture reaction in two designs. The TARC method was composed of moderating neutrons in lead or a composition of lead and water. Additionally, the target was surrounded by a moderator assembly and a graphite reflector district. Produced neutrons were investigated by (p,xn) interactions with 30 MeV and 300 μA proton beam on tungsten, beryllium, and tantalum targets. The ⁹⁹Mo production yield was related to the moderator property, cross section, and sample positioning inside the distinct region of neutron storage as must be proper to achieve gains. Gathered thermal flux of neutrons can contribute to molybdenum isotope production. Moreover, the sample positioning to gain higher production yield was dependent on a greater flux in the length of thermal neutrons and region materials inside the moderator or reflector. When the sample radial distance from Be was 38 cm inside the graphite region using a lead moderator design, the production yield had the greatest value of activity, compared with the other regions, equal to 608.72 MBq/g. Comparison of the two designs using a Be target revealed that the maximum yield occurred inside the graphite region for the first design at 38 cm and inside the lead region for the second design at 10 cm. The results and modeling of the new neutron activator were very encouraging and seem to confirm that the TARC concept can be used for ⁹⁹Mo production in nuclear medicine.     

Structure investigations of solid organosilicon polymers by high resolution solid state 29Si NMR

The high resolution ²⁹Si NMR spectra of five solid silicon polymers of different structure have been studied and the ²⁹Si chemical shifts of characteristic structure units determined. ²⁹Si¹H cross-polarization in combination with high speed magic angle sample spinning and high power proton decoupling was used to achieve high resolution in the solid state spectra. Comparison of the latter with the results obtained in the liquid state clearly indicates that no special solid state effects on ²⁹Si chemical shifts arise and the relations between δ(Si) and the molecular structure, well known from investigations of liquids, can be used for interpretation of the solid state spectra. It is shown that high resolution solid state ²⁹Si NMR spectroscopy offers detailed information about the structural units of the siloxane resin framework, and this opens up new possibilities for structural determinations of solid organosilicon polymers.     

Structure investigations of solid organosilicon polymers by high resolution solid state Si NMR

The high resolution ²⁹Si NMR spectra of five solid silicon polymers of different structure have been studied and the ²⁹Si chemical shifts of characteristic structure units determined. ²⁹Si---¹H cross-polarization in combination with high speed magic angle sample spinning and high power proton decoupling was used to achieve high resolution in the solid state spectra. Comparison of the latter with the results obtained in the liquid state clearly indicates that no special solid state effects on ²⁹Si chemical shifts arise and the relations between δ(Si) and the molecular structure, well known from investigations of liquids, can be used for interpretation of the solid state spectra. It is shown that high resolution solid state ²⁹Si NMR spectroscopy offers detailed information about the structural units of the siloxane resin framework, and this opens up new possibilities for structural determinations of solid organosilicon polymers.     

Reactor neutrons irradiation effect on the photocatalytic activity of SnO<Subscript>2</Subscript> thin films

SnO₂ thin films synthesized by sol-gel are irradiated with reactor neutrons up to fast neutron fluence of 9.6 × 10¹⁷ neutrons cm^–2 at 40°C. The influence of defects generated by neutrons irradiation, through the properties modification, on the photo-catalytic activity of SnO₂ films is investigated. It is found that the photoactivity of the irradiated films is enhanced after reactor neutrons irradiation. An improvement of 41% is observed for the sample irradiated at a neutron fluence of 9.6 × 10¹⁷ neutrons cm^–2. This is attributed to several parameters modified by the reactor neutron irradiation principally the crystallite size and space charge region which are closely related to the photocatalytic performance.     

A nuclear microprobe method for the simultaneous determination of silicon and nitrogen profiles in metals

A nuclear microprobe method has been developed for the simultaneous determination of silicon and nitrogen concentration profiles in metals. The method was based on the reactions²⁸Si(d, p₀)²⁹Si and¹⁴N(d, p₀)¹⁵N plus¹⁴N(d, β₀)¹²C with measurement of emitted charged particles during irradiation with 1.9 MeV deuterons. The nitrogen sensitivity was ten times that for silicon and the minimum concentrations detected were 0.002% and 0.03% respectively. The method was successfully applied to the measurement of silicon and nitrogen profiles in alloys contacted with silicon nitride at high temperature.