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.     

An oxygen standard for the determination of oxygen in steel by 14-MeV neutron activation analysis

A relative method for the determination of oxygen in steel via the ¹⁶O(n,p)¹⁶N reaction by means of 14-MeV neutrons is described. A standard is irradiated immediately behind the sample and the induced activities are counted simultaneously with two separate but identical detector systems. The standard mixture (ca. 5 g of graphite plus iron oxide containing 80 mg of oxygen per g) is compressed into a steel capsule of the same external dimensions as the samples (26 mm diameter, 9 mm thick). Dimensional tolerances, choice and purity control of the oxygen compound and preparation of the standard mixture are discussed. Fast neutron shielding, absorption of fast neutrons, self-absorption of the ¹⁶N /gg-rays and the average neutron flux in sample and standards are considered and a total correction factor is established. Flux inhomogeneities and differences in counting geometry and discriminator setting can be determined by irradiation and counting of two identical standards. The accuracy of this method was checked by comparison of the results with those of the reducing fusion method; satisfactory agreement was observed, although the activation results tended to be slightly higher. The mean long-term standard deviation for analysis of a given sample over a period of 6 months was found to be ±3%.     

Application of the radioreagent method for yield determination in neutron activation analysis

A very convenient method for yield determination in NAA is the use of isotopic radiotracers. But for the majority of elements determinable by NAA no suitable isotopic radiotracers exist. For some of these elements the radioreagent methodoffers afvourable opportunity to use also non-isotopic radiotracers. An activation analytical copper determination method is described using a radioactively labelled reagent for correction of separation losses. Results of copper determinations in 8 international standard reference materials are given.     

Non-destructive determination of aluminium,silicon and oxygen in steel by 14 MeV neutron activation analysis

Analysis of steel for aluminium, silicon and oxygen is presented. The use of a Ge(Li) detector and the technique of precise photopeak integration enabled to attain a detection limit of 0.04% for Al. A method of the evaluation of the iron interference in silicon determinations is proposed.     

Accurate fast neutron activation analysis for oxygen in geological materials

Sources of error in the fast neutron activation analysis determination of oxygen have been investigated and minimised. The oxygen contents of eighteen international rock standards and a sulphide ore standard have been determined, and compared with the values calculated by difference using the reported full analyses. Accuracies of 0.3% average deviation and reproducibilities of ±0.2% standard deviation have been obtained, where oxygen contents exceeded 1.0 g.     

The determination of niobium in steel by neutron activation

A method is described for determination of niobium in steels by neutron activation analysis. It is applicable to samples containing down to 3 μg of niobium; but this sensitivity may be improved by a factor of 10 by use of a thin beryllium, window crystal for counting. The time necessary for the analysis is about l h.     

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.      

Nitrogen determination in plant samples by fast neutron activation analysis

For the non-destructive deermination of the nitrogen content in plant samples 14-MeV neutron activation analysis was applied. Using powder samples of 0.7 g, irradiation time of 1 h and measuring time of 10 min, the accuracy of the determination is about +15%. The potassium content of the plant samples was determined by X-ray fluorescence analysis and correction was made for their contribution to the nitrogen activities.This work was supported in part by the Hungarian Academy of Sciences.     

Protein determination in soya bean by fast neutron activation analysis

For a non-destructive determination of the protein content in soya bean samples, 14-MeV neutron activation analysis /NAA/ was applied. To check the method, results obtained by X-ray fluorescence /XRF/ analysis and the Kjeldahl procedure were compared. For pressed pellet samples of about 1 g and choosing 15 min irradiation and 10 min measuring times the accuracy of the protein determination was found to be 15%.This work was supported by the Hungarian Research Foundation /Contract No. 259/.     

Vacuum emission spectrometric determination of oxygen in iron and steel

Summary A method is described for the determination of the oxygen content of steels by means of a ultraviolet vacuum-spectrographic method. A d.c. carbon arc discharge was used to extract the oxygen as carbon monoxide from the sample. The intensity ratio of OI 1302.17 Å/CII 1721.66 Å was used on the condition of 200 V, 60 F, 18 A and the argon pressure of 600 mm Hg. The oxygen can be determined within a concentration range of 0.008 to 0.08% in various steel samples with a variant coefficient of 8 to 17%.

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Zusammenfassung Zur Bestimmung des Sauerstoffgehaltes von Stählen wird eine UV-vakuumspektrometrische Methode empfohlen. Eine Gleichstrom-Bogenentladung an der Graphitelektrode wird benutzt, um den Sauerstoff aus den Proben als Kohlenmonoxid zu extrahieren. Das Intensitätsverhältnis von OI 1302.17 Å/CII 1721.66 Å wird unter den folgenden Anregungsbedingungen gemessen: 200 V, 60 F, 18 A, Argondxuck 600 mm Hg. Sauerstoffgehalte von 0.008–0.08 % in verschiedenen Stählen werden mit einer Standardabweichung von 8–17% bestimmt.

     

The determination of fluorine in bone by fast neutron activation analysis

A routine method is presented for the determination of fluorine in small bone samples by activation analysis with fast conversion neutrons. Both the purely instrumental determination and the analysis by chemical separation are discussed. The activations are performed with the AVF cyclotron of Philips-Duphar at Petten. Use was made of a rabbit system equipped with a Be-target, which can be inserted in the internally deflected beam of the cyclotron. The sensitivity of the instrumental method is ≈1 μg. Application of chemical isolation results in a sensitivity of ≈0.1 μg.     

A simple and fast method for the determination of active ingredient in antiperspirant cosmetics by neutron activation analysis

Antiperspirant cosmetics are tested for their active ingredient (aluminium chlorohydroxide) by conventional analytical techniques. Aluminium has been determined by instrumental neutron activation analysis in all antiperspirant products and package forms available in the Greek market in order to develop a simple and fast method for its quantitation. Our results show that neutron activation analysis could be established as an official method for the determination of active ingredient in antiperspirant cosmetics. The proposed method is compared with the existing official methods and an alternative sampling method for aerosol package is presented.     

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.     

The determination of sulphur and phosphorus in steel by neutron activation analysis

Sulphur and phosphorus in steel were determined by neutron activation analysis, being counted as ³⁵S and ³²P respectively. For steels with sulphur to phosphorus ratios larger than 10, it seems possible to determine both elements by counting ³²P, making use of a double irradiation technique at different fast to slow neutron fluxes.     

A rapid calibration method for the determination of traces of oxygen by 14-MeV neutron activation analysis

A dual axis rotation irradiation system has been used in the development of a calibration method for the determination of oxygen in almost any matrix by 14-MeV neutron activation. The method allows the correction of matrix effects which arise from neutron removal and γ-self absorption, thus providing an accuracy of ± 2% for the oxygen analysis. The experimental results are interpreted on the basis of theoretically calculated mass absorption coefficients and neutron removal cross-sections.     

A direct read-out system for fast neutron activation analysis for oxygen in steels

Fast neutron activation is useful for rapid determinations of oxygen in iron and steel, but the conventional calculations are tedious A direct read-out system is described so that results are immediately available.     

Determination of lanthanum in large steel samples by the neutron activation method

In view of the inhomogeneous distribution of lanthanum in steel, large samples should be used for the determination of this element. The method elaborated consists in the preparation of an average samople by dissolving 50 g steel and analysing an aliquot of the obtained solution corresponding to 0.5 g of steel. In order to reduce the activity of the sample, iron and some other elements are separated from the steel solution by electrolysis prior to irradiation. The amount of lanthanum contamination introduced during the pre-irradiation treatment of the sample is relatively low (10^?10–10^?9 g) if the treatment is carried out under suitable conditions. The post-irradiation treatment consists in the separation of²⁴Na by shaking the sample solution with Sb₂O₅. The¹⁴⁰La-activity is measured by means of a γ-spectrometer (1.6 MeV photopeak).     

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.     

The use of threshold energy differences in fast neutron activation analysis for oxygen and fluorine

A method is described for the simultaneous determination of oxygen and fluorine; the latter has a lower neutron-activation threshold energy so that the fluorine-to-oxygen¹⁶N formation ratio changes after partial moderation of the incident 14.7 MeV neutron beam. In mixtures containing approximately equal amounts of fluorine and oxygen, these elements can each be determined with a precision of ca. ±1%; as expected, errors in the determination of a minor component (ca. 17%) are larger, being ca. ±5%.     

Corrections for carbon and oxygen interference in the 14-MeV neutron activation determination of nitrogen

Reactions in the carbon and oxygen atoms of sample matrix can lead to errors in the 14 MeV neutron activation determination of nitrogen based on the¹⁴N(n, 2n) reaction, particularly as a consequence of proton-induced reactions leading to¹³N formation in samples of an organic nature. In this study, the extent of such interferences have been evaluated by measuring the apparent N contribution when a series of alcohols and a water sample were irradiated with 14 MeV neutrons from a Texas-Nuclear neutron generator under the same conditions used for trace N determination and contributions amounting to from 0.1 to 1% apparent N content observed (and corrected for). Owing to neutron flux in stabilities and assymetries, flux monitoring was done with aluminum foils on either side of the samples for N analysis, and which were counted for²⁴Na. Two samples of foodstuff were analyzed correction for C and O interference, agreed with conventional analysis within ±10%.