Internal standard activation analysis of silicon in steel

Non-destructive 14-MeV neutron activation analysis for silicon in steel has been applied with ⁵⁶Mn as internal standard.⁵⁶Mn is formed from the iron matrix via the ⁵⁶Fe(n,p)⁵⁶Mn reaction. Several methods of internal standardisation via⁵⁶Mn are discussed. The 0.84-MeV photopeak of ⁵⁶Mn is recommended if steel samples of about the same composition are to be analysed. Chemically analysed steel samples are used as silicon standards. A precision of 0.7% was obtained for an analysis plus standardisation time of 13 min. Special attention was paid to interferences produced by concentration changes of impurity elements. Several possible sources of errors were investigated.     

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.     

Application of inelastic proton scattering to the rapid determination of silicon in steels

A rapid, nondestructive method for the determination of silicon in steels has been developed based on the measurement of the 1.77-MeV γ-line emitted by the proton inelastic scattering reaction ²⁸Si(p,p')²⁸Si For some of the determinations the 0.84-MeV γ-line from the reaction ⁵⁶Fe(p,p')⁵⁶Fe was used as internal standard.     

Simultaneous determination of chromium and silicon in steel by 14-mev neutron activation analysis

Chromium and silicon are determined simultaneously in steel by 14-MeV neutron activation analysis. The activities of ⁵²V(E_γ=1.43 MeV,T_{$\text{1}\text{2}$}=3.76 min) from ⁵²Cr(n,p)⁵²V and ²⁸Al (E_γ=1.78 MeV; T_{$\text{1}\text{2}$}=2.24 min) from ²⁸Si(n,p)²⁸Al are evaluated by mixed γ-ray spectrometry. The influence of manganese and phosphorus, the main interfering elements, is negligible for most stainless steels. The count rate should be limited, to avoid ⁵²V pulse pile-up effects interfering in the ²⁸Al energy region. Precisions in the 2-10% range are reached, depending on the concentrations, for a 10-min analysis time. Results for a series of steel samples are compared with industrial analyses.     

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.     

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.     

Oxygen determination by fast neutron activation

A method for the determination of oxygen based on the reaction¹⁶O(n, p)¹⁶N is suggested. The samples are irradiated in stainless steel capsules with fast neutrons. The total neutron flux passing through the sample is proportional to the flux passing through the wall of the capsule. Therefore, the activity induced in the capsule according to the reaction⁵⁶Fe(n, p)⁵⁶Mn can be used to monitor the neutron flux through the sample. Thus, the necessity of maintaining the sample in an exact position during the irradiation is eliminated.     

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.     

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.     

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.     

Radio-isotope neutron activation analysis for vanadium,manganese and tungsten in alloy steels

An instrumental neutron activation method for V, Mn and W in alloy steels with a ²⁴¹ Am/Be isotopic neutron source is described. The samples were irradiated to induce the nuclear reactions ⁵¹V(n, γ) ⁵²V, ⁵⁵Mn(n, γ)⁵⁶Mn, and ¹⁸⁶W(n, γ)¹⁸⁷W. The activities were measured with a NaI(TI) detector. Interferences on the measured photopeaks were shown to be negligible by measuring the half-lives of ⁶²V, ⁵⁶Mn and ¹⁸⁷W.These thre elementes were determined in the range 1.5–12.9% in special steels; manganese in the range 0.5–1.6% was measured in cast irons. Calibration was done by comparison with results from wet chemistry and x-ray fluorescence spectrometry. The processing times for the vanadium, manganese and tungsten determinations were 11 min, 3 h and 26.3 h, respectively, but these were reduced greatly by intoruding a scheme wherein six samples were simultaneously irradiated and the ⁵⁶Mn and ¹⁸⁷W nuclides were measured sequentially for a series of 66 samples. The average processing time was reduced to 45 min for tungsten with a precision of 4.0% and accuracy of 3.4% and 22.8 min for manganese with a precision of 3.8% and accuracy of 3.1%.     

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.     

Fast neutron activation analysis of bulk coal samples for alumina,silica and ash

The fast neutron activation technique was applied to bulk samples (≈11 kg) of Australian black coal. The determination of alumina is based on the reaction ²⁷Al(n,p)-²⁷Mg by counting the 0.844-MeV peak (t_{$\text{1}\text{2}$} = 9.4 min). Silica is determined by means of the reaction ²⁸Si(n,p)²⁸Al; the 1.78-MeV peak (t_{$\text{1}\text{2}$} = 2.3 min) is counted and a correction for the interference from alumina is applied. The ash content is based on the correlation between ash and the sum of alumina and silica. The accuracies (1 SD) for the determination of alumina, silica and ash were 0.52% Al₂O₃, 0.79% SiO₂ and 1.02% ash, respectively. The ash, alumina and silica contents of the samples were in the ranges 8.8–37.5%, 1.3–10.3% and 6.4–22%, respectively.     

SIACON—Equipment for the on-line determination of the silicon content of coal

The paper describes an automatic equipment which allows to determine the silicon content of coal by neutron activation analysis. The technique is based on the measurement of gamma-ray intensity of the²⁸Al radionuclide, which is the result of the fast neutron reaction²⁸Si(n, p)²⁸ Al. The Activation part includes a Pu-238/Be neutron source which is located in the middle of the sample container; the measuring part includes two NaI(Tl)-scintillation counters. The total time of the anlysis of one sample amounts to a few minutes; the standard deviation of a single determination is 0.2% SiO₂.     

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.     

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.     

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.     

Determination of pit-coal ash content with the use of an (α, n) neutron source

Activation with fast neutrons from a Pu/Be source enables the ²⁸Si(n, p)²⁸ Al and ²⁷Al(n p)²⁷Mg reactions to be utilized. Seventy-two samples of pit coals with ash contents ranging from 3 to 40% were measured. The calibration function between ash content and both 1.78- and 0.84-MeV γ-ray counts was linear. The standard deviation was 0.9% for a 17% ash content and 1.4% over the whole range of ash contents. Comparison with other methods is discussed.     

Determination of silicon in natural and pollution aerosols by 14-MeV neutron activation analysis

The determination of silicon via the ²⁸Si(n,p)²⁸ Al reaction by means of 14-MeV neutrons is applied to the analysis of pollution and natural aerosols. A Whatman 41 filter (40 cm²) on which airborne particulate material has been collected is compressed into a 3 × 12.7 mm pellet. Standards are prepared in the same way from clean filters spiked with a silicate solution. After a 50-s irradiation and a 75-s decay time, the sample is counted for 2 min with 5” × 5” NaI(Tl) well detector. The 1.779-MeV photopeak of ²⁸Al is measured with a single channel sealer chain or with a multichannel analyser. The reproducibility, sensitivity and liability to interference from other elements were investigated for both counting systems. The homogeneity of the pellets and the filters was checked. The overall precision of one single-channel determination was estimated to be 3.5% after a 24-h high-volume sampling time. Samples collected in urban, industrial and remote areas with concentrations ranging from 0.05 to 15 μg Si m^-3 air were analysed and the results are discussed.     

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.