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.     

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.     

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.     

A quick method for the determination of the Al/Si weight ratio in alumino-silicates using an Am-Be neutron source

An irradiation procedure with fast and thermal neutrons from a 5 Ci Am-Be isotopic neutron source irradiation facility in combination with a 3'3' NaI(Tl) detector system has been used to determine Al/Si weight ratios in alumino-silicates. Samples were irradiated with and without Cd cover for 10 minutes and counted for 10 minutes after a waiting time of 1 minute. The peak area analysis of the 1779 keV gamma-ray line of ²⁸Al product radionuclide produced via ²⁷Al(n,γ)²⁸Al and ²⁸Si(n,p)²⁸Al reactions in combination with the neutron flux parameter at the irradiation site and nuclear data were used to determine Al/Si ratios. Due to discrepancy in literature data, Am-Be neutron source spectrum averaged cross sections of (n,p) reactions on ²⁷Al, ²⁸Si and ⁵⁶Fe were determined by the activation technique using ¹¹⁵In(n,n')^115mIn as the fast neutron flux monitor reaction. The method was tested using mixtures of high-purity Al₂O₃ and SiO₂ with known weight ratios of Al/Si and validated by a certified reference material BCS-CRM 348 (Ball Clay). Results are presented for bentonite, kaolin, bauxite, feldspar and ball clay samples from Nigeria. The method is non-destructive, rapid and suitable for use in-situ for large-scale exploration works and industrial process control. This revised version was published online in July 2006 with corrections to the Cover Date.     

Method for simultaneous determination of Al and Si in atmospheric aerosols by 14 MeV neutron activation analysis

The 14 MeV neutron activation facility of the Hohenheim University is described and the calculated determination limits for 20 elements are presented. The determination of aluminium via the²⁷Al(n, p)²⁷Mg reaction and of silicon by the²⁸Si(n, p)²⁸Al reaction is applied to the analysis of atmospheric aerosols. A running program for routine analyses was elaborated. The method was checked with the aid of an intercomparison sample.     

29Si-NMR-Untersuchungen zur Verteilung der Silicium-und Aluminiumatome im Alumosilicatgitter von Zeolithen mit Faujasit-Struktur

²⁹SiNMR Investigation of Silicon-Aluminum Ordering in the Aluminosilicate Framework of Faujasite-Type Zeolites The high resolution magic angle spinning ²⁹Si NMR spectra of a series of NaX and NaY zeolites with Si/Al ratios of 1.18 to 67 exhibit up to five sharp signals which could be assigned to the central silicon atoms of Si(OSi)_4–n(OAl)_n building units (n = 0–4) of the aluminosilicate framework. From the signal intensities the quantitative distribution of the building units and the Si/Al ratio of the aluminosilicate lattice have been estimated. By comparison of the building units obtained from the ²⁹Si NMR spectra with those from theoretical model structures detailed information on silicon-aluminum ordering of the zeolite framework has been derived. Except for NaX of Si/Al = 1.4 a centrosymmetrical distribution of Si and Al atoms within a double-cubooctahedra unit has been found which agrees well with the Si/Al ordering scheme proposed by Dempsey.     

Use of the Absolute Parametric Method to Evaluate the Analytical Significance of Threshold Reactions on P, Si, Al and Mg by NAA

We investigated the use of threshold reactions on magnesium, aluminum, silicon and phosphorus to determine elemental concentrations and also to correct analytical interferences, using the parametric method. The reactor neutron spectrum averaged cross sections of the threshold reactions on these elements were referred to the (111±3) mb value for the ⁵⁸Ni(n,p)^58g+mCo reaction cross section. The results of the cross section measurements are: ²⁵Mg(n,p)²⁵Na, 1.57±0.12 mb; ²⁸Si(n,p)²⁸Al, 5.68±0.25 mb; ²⁹Si(n,p)²⁹Al, 3.02±0.15 mb; ³⁰Si(n,)²⁷Mg, 0.1346±0.0090 mb; and ³¹P(n,)²⁸Al, 1.912±0.083 mb. The values for the cross sections of the following reactions: ²⁴Mg(n,p)²⁴Na, 1.441±0.092 mb; ²⁷Al(n,p)²⁷Mg, 3.84±0.18 mb; and ²⁷Al(n,)²⁴Na 0.721±0.028 mb were re-measured to check the methodology. We present the application of these values to the analysis of some reference materials.     

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.     

Fast neutron activation analysis of silicon in aluminum alloys

The silicon content in an aluminum-silicon alloy was measured by nondestructive fast neutron activation analysis with fission spectrum neutrons. A boron nitride irradiation container reduced the flux of thermal and epithermal neutrons at the sample position, enhancing the²⁹Si (n, p)²⁹Al reaction. A detection limit of 0.4% silicon in a 0.5 g alloy sample was obtained.     

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.     

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.     

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.     

Application of fast solvent extraction processes to studies of exotic nuclides

The nucleus²³Na has been investigated by studying the primary γ-rays emitted from 53 keV neutron capture in it using a high resolution and high efficiency (100%) HPGe detector and NaI(T1) detector for anti-Compton. 24 primary γ-rays were placed in the²⁴Na, in which 3 primary γ-rays were new ones from a (n, γ) reaction, and reported for the first time. In order to obtain an exact energy calibration within 7 MeV,⁵⁶Fe(n,γ)⁵⁷Fe reaction was used at thermal neutron energy. Intensity calibration was obtained from the²⁷Al(p,γ)²⁸Si reaction atE _p=2046 keV. The neutron binding energy of²⁴Na was determined to be 6959.75 keV.     

The Detection and Reactivity of Silanols and Silanes Using Hyperpolarized 29Si Nuclear Magnetic Resonance

Silanols and silanes are key precursors and intermediates for the synthesis of silicon‐based materials. While their characterization and quantification by ²⁹Si NMR spectroscopy has received significant attention, it is a technique that is limited by the low natural abundance of ²⁹Si and its low sensitivity. Here, we describe a method using p‐H₂ to hyperpolarize ²⁹Si. The observed signal enhancements, approaching 3000‐fold at 11.7 T, would take many days of measurement for comparable results under Boltzmann conditions. The resulting signals were exploited to monitor the rapid reaction of tris(tert‐butoxy)silanol with triflic anhydride in a T₁‐corrected process that allows for rapid quantification. These results demonstrate a novel route to quantify dynamic processes and intermediates in the synthesis of silicon materials.     

Simultaneous determination of silicon and phosphorus in cast iron by 14 MeV neutron activation analysis

A fast (10 min), non-destructive simultaneous determination of silicon and phosphorus in cast iron and steel by 14 MeV neutron activation was developed. The 1.78 MeV²⁸Al activity (T=2.24 min) induced by the reaction²⁸Si(n, p)²⁸Al is counted on a NaI(Tl) detector. Two measurements are made to correct for the 1.81 MeV⁵⁶Mn activity (T=2.58 hr) from the iron matrix. However,²⁸Al is also produced via³¹P(n, α)²⁸Al. By (n, 2n) reaction, phosphorus yields also³⁰P (T=2.6 min), the 0.511 MeV annihilation radiation of which is counted by two opposite NaI(Tl) detectors in coincidence. Again, two successive coincidence measurements are carried out in order to take into account the⁵³Fe activity (β⁺; T=8.9 min) from⁵⁴Fe(n, 2n)⁵³Fe. The²⁸Al measurement is appropriately corrected via the computed phosphorus content. An oxygen flux monitor was used to normalize to the same flux. Nuclear interferences have been examined. Special attention has been paid to the presence of copper. The standard deviation for phosphorus being as high as ca. 0.09% P for a single determination, this technique can only be practical as an independent phosphorus analysis for high phosphorus cast irons. The precision on the²⁸Al measurement is 5% relative for 0.2% Si and 2.5% above 1% Si. Aspirant of the N.F.W.O.     

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.     

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.     

NAA determiantion of iron and silicon in USGS standards and bauxites using fast neutrons from241Am-Be source

Fast neutron-activation methods have been developed for the determination of iron and silicon in USGS and Indian standards and bauxites. Nuclear reactions⁵⁶Fe/n, p/⁵⁶Mn and²⁸Si/n, p/²⁸Al were carried out using²⁴¹Am-Be neutron source and cutting off thermal neutrons with a Cd shield. For Si a cyclic method was adopted due to short half life of²⁸Al /2.3 min/. The methods are non destructive, fast, economic and ideal for bulk analysis of rocks and process control.A part of this work was presented at the International Symposium on Nuclear Analytical Chemistry, Slowpoke Reactor Facility, Dalhousie University, Canada, June 5–7, 1985.     

On the determination of silicon in pottery

To study the nature of ancient and modern pottery it is necessary to be able to determine the concentrations of the major constituent elements. For such studies, mass balances calculated from these elemental concentrations cluster around 100% for a silicate-silica matrix and around 80–90% in highly calcarious pottery which has a silicate-carbonate (silica) matrix. This work requires experimental measurements with coefficients of variation wihtin approximately ±5%. The high concentrations of silicon in pottery may reasonably be determined by neutron activation analysis using the nuclear reaction²⁹Si(n, p)²⁹ Al. Aluminium-29 has a half life of 6.56 minutes and a γ-ray energy of 1272 keV. Epithermal neutron irradiations of samples in cadmium foil are required to minimize the quantities of thermal neutron induced radionuclides. The method of analysis developed for the low flux SLOWPOKE reactor is described and the accuracy and precision of the technique is discussed by allusion to analyses of standard reference materials. The application of this technique to two different archaeological problems is addressed. The first is a case of carbonate dilution found in neolithic pottery from Iran and the second case is a problem of silica dilution in Roman pottery from Germany.     

A method for the determination of additive elements in sintered tungsten metal rods by fast neutron activation analysis

A non-destructive activation analytical method developed for the determination of the axial concentration distributions of Al, Si and K residual additives in sintered tungsten rods is briefly described. A 14 MeV neutron generator is used to produce the reactions²⁷Al(n, p)²⁷Mg,²⁸Si(n, p)²⁸Al and³⁹K(n, 2n)³⁸K and the activities are compared with standards. A weighted least-squares fitting program is used for peak area determination of the scintillation spectra. A scheme of the irradiating and measuring arrangement with a pneumatic sample-transfer system is presented. The system is applicable to large-scale routine analysis and lends itself well to automation. The results of preliminary measurements with this arrangement are given.