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.     

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.     

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 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.     

Rapid determination of molar ratios in binary systems by 14 MeV neutron activation analysis

The magnetic characteristics of barium ferrite, a compound widely used for magnetic materials, depend on the molar ratio of iron(III) oxide to barium oxide. On account of this fact, activation analysis using 14 MeV neutrons was applied for the rapid and non-destructive determination of the molar ratio of iron(III) oxide to barium oxide in barium ferrite. Iron was detected as⁵⁶Mn produced from the⁵⁶Fe(n, p)⁵⁶Mn reaction, and barium as^137mBa originating from the¹³⁸Ba(n, 2n)^137mBa reaction. A linear relation was obtained between the ratio of counts of⁵⁶Mn and^137mBa and the molar ratio of iron(III) oxide to barium oxide; the corrected gradient of the experimental calibration curve, obtained with^137mBa internal standard, agreed well with the calculated value. The molar ratios of iron(III) oxide to barium oxide obtained by activation analysis and by chemical analysis were in good agreement.     

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.     

Rapid determination of molar ratios in binary systems by 14 mev neutron activation analysis

The 14 MeV neutron activation analysis method was applied for the rapid and non-destructive determination of the molar ratios of iron(III) oxide and zinc oxide in zinc ferrites. Iron was detected as⁵⁶Mn produced from⁵⁶Fe by the (n, p) reaction, and zinc as the sum of the coincidence counts of the annihilation radiations of the positrons emitted from⁶³Zn and⁶⁴Cu produced from⁶⁴Zn by the (n, 2n) and (n, p) reactions respectively. The ratios of the counts of⁵⁶Mn and the sum of the coincidence counts were not linearly related to the molar ratios of iron(III) oxide and zinc oxide in zinc ferrites. However, by corrections of the mutual contributions to the counts, linear relations were obtained between the ratios of the counts and the molar ratios when the corrected sum of the coincidence counts was used as an internal standard. The experimental and theoretical slopes of the analytical lines agreed within a difference of approximately 10%. The deviations between the results of the activation analysis and those of the chemical analysis were less than 5% of the chemical results.     

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.     

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.     

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.     

铸铁中硅、磷、钼等九种元素的ICP-AES测定

采用ＩＣＰ－ＡＥＳ对铸铁中硅、磷、钛、钼、镍、锰、铬、铝和铜杂质的测定进行了研究。考察了铁对待测元素的干扰情况，发现铁对铜有光谱尾翼干扰，干扰系统为１．０×１０－５。采用不同的酸溶解样品时，硅的测定结果有显著的差别。     

Photon and proton activation analysis of iron and steel standards using the internal standard method coupled with the standard addition method

The internal standard method coupled with the standard addition method has been applied to photon activation analysis and proton activation analysis of minor elements and trace impurities in various types of iron and steel samples issued by the Iron and Steel Institute of Japan (ISIJ). Samples and standard addition samples were once dissolved to mix homogeneously, an internal standard and elements to be determined and solidified as a silica-gel to make a similar matrix composition and geometry. Cerium and yttrium were used as an internal standard in photon and proton activation, respectively. In photon activation, 20 MeV electron beam was used for bremsstrahlung irradiation to reduce matrix activity and nuclear interference reactions, and the results were compared with those of 30 MeV irradiation. In proton activation, iron was removed by the MIBK extraction method after dissolving samples to reduce the radioactivity of⁵⁶Co from iron via⁵⁶Fe(p,n)⁵⁶Co reaction. The results of proton and photon activation analysis were in good agreement with the standard values of ISIJ.     

Fast determination of the tin content in cassiterite ores by photon activation method

Photon activation analysis has been success-fully applied to the fast and non-destructive analysis of tin in cassiterite ores based on the 159.7 keV gamma line of^123mSn produced in the¹²⁴Sn/γ, n/^123mSn reaction. In order to improve the accuracy of analytical results, corrections for self-absorption and pile-up effects were performed. Under typical conditions /15 μA electron beam current, 15 MeV bremsstrahlung energy, 5 min irradiation time and 10 min measurement/ the sensitivity of the analysis is 10 ppm. The proposed method can be used for routine analysis of tin in geological samples.     

Heteropoly acids in the determination of phosphorus by neutron activation analysis

Phosphorus is selectively extracted as molybdovanadophosphoric acid (MVPA) and determined indirectly using⁵²V. Silicon, germanium, arsenic, fluoride and tannic acid do not interfere. The sensitivity for phosphorus was 1421±13 counts⁵²V per ng P ml^–1 with a detection limit of 0.2 ng P ml^–1. The precision is ±10% over the range 0.7±70 ng P ml^–1. The sensitivity is four orders of magnitude greater than for conventional neutron activation analysis (NAA) using the³¹P(n, )²⁸ Al reaction and a SLOWPOKE II reactor. Greater selectivity for phosphorus is obtained than by direct measurement of³²P by beta ray spectroscopy.     

Neutron activation method for nitrogen determination in biological specimens

For the determination of the nitrogen content in plants, 14 MeV neutron activation analysis was used based on the determination of the elemental concentration by measuring the area of the gamma-radiation of the radionuclide¹³N as a result of¹⁴N(n, 2n)¹³N reaction. Three methods were tested in order to obtain quantitative results: comparator method, method for absolute determination of the neutron flux and monitor method. Using the monitor method, results for nitrogen content in plant species were obtained-for beans 74.8% and for maize 1.8%. The precision of determination is ±10%. The possible sources of errors are analyzed. The efficiency of the Ge(Li) detector has been determined using a combined -source in the energy interval 120–1400 keV with precision of 4.5%. The sensitivity achieved was 4 mg or 47 imp/mg per min.     

Preparation of manganese-53

The nuclide⁵³Mn was produced by the following three nuclear reactions,⁵²Cr(d, n)⁵³Mn,⁵¹V(³He n)⁵³Mn and⁵⁰Cr(α, n), (α, p)⁵³Mn. Enriched⁵²Cr and⁵⁰Cr metal targets were prepared on copper plate holder by electrodeposition. The commercially available natural vanadium foil was used for the⁵¹V(³He, n)⁵³Mn reaction. Each target was bombarded in a cyclotron. Manganese was extracted and purified without using carrier from the bombarded targets by anion and cation exchanges and solvent extraction. The isotopic ratio⁵³Mn/⁵⁵Mn was measured by mass spectrometry and the amount of⁵⁵Mn was determined by neutron activation analysis. The activity of⁵³Mn obtained was 7 dpm by 750 millicoulombs in³He bombardment (E³He=20 MeV). The activity due to by-product⁵⁴Mn was about several thousands times higher than that of⁵³Mn in³He and deuteron bombardments, which were produced through⁵¹V(³He, γ)⁵⁴Mn and⁵³Cr(d, n)⁵⁴Mn. In alpha bombardment (E_α=15 MeV), the activity of⁵³Mn produced was 8 dpm by 95 millicoulombs. The activity ratio, dpm⁵⁴Mn/dpm⁵³Mn, was about 3, and this ratio was the best one among the results so far obtained.     

In vitro activation of bone with 14 MeV neutrons

Samples of compact bone, bone marrow and spongiosa of cow femur have been irradiated in vitro with 14 MeV neutrons. The Ca/P ratio for compact bone was found to be 2.16±0.24. The suitability of using 14 MeV neutrons and the³¹P(n, α)²⁸Al reaction for studying the bone mineral composition in vitro is discussed.     

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%.     

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.     

Precise determination of half-lives of56Mn,193Os and197,199Pt

The half-lives of⁵⁶Mn,¹⁹³Os and^197,199Pt have been remeasured with better precision compared to previous valeus.