Activation analysis of high-purity silicon

The triple comparator method is used for the analysis of impurities of high purity silicon by neutron activation. The ratios of the specific photopeak activities of the isotopes investigated to the specific photopeak activities of the gold, indium and cobalt comparators were determined. The triple comparator method avoids some tedious problems in the multi-element activation analysis and it is very well suited for the determination of ‘non-expected’ elements. Research associate of the N. F. W. O.     

Activation analysis of biological maternal with ruthenium as a multi-isotopic comparator

The elements Fe, Zn, Se, Rb and Co were determined in NBS bovine liver (SRM 1577) by non-destructive activation analysis; ruthenium was used as triple comparator element. The results were compared with the values of the analysis certificate and with those of an analysis based on a multi-element serum standard; the agreement was excellent. The conclusions of the error theory of the comparator method were experimentally confirmed.     

Zirconium as a multi-isotopic flux ratio monitor and a single comparator in reactor-neutron activation analysis

Different methods for the determination of thermal-to-epithermal neutron flux ratio are reviewed and nuclear data for commonly used monitor materials and for Zr isotopes are tabulated. It is shown that the use of the⁹⁴Zr−⁹⁶Zr isotope pair gives significant improvement in precision while measuring Φ_th/Φ_e ratios in the 20<Φ_th/Φ_e<200 range. When the single comparator method is applied, the use of the⁹⁴Zr isotope is suggested as a comparator with the⁹⁴Zr−⁹⁶Zr isotope pair for simultaneous flux ratio determination. Theoretical calculations show that the Zr comparator-flux ratio monitor gives better precision and accuracy than does Ru for two-thirds of the isotopes used for analysis in well thermalized (Φ_th/Φ_e>100) channels. The I_o/σ_th-values for the mentioned Zr isotopes have been experimentally determined and compared with previously published data. Research associate of NFWO.     

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%.     

Experimental comparison of multi-channel analyzer. Dead-time corrections for short-lived radionuclides

The accuracy of the live-time circuit of a 400-channel analyzer was studied in detail, and was found to be unsatisfactory even for long-lived radionuclides. It was found that automatic live-time correction with the multi-channel analyzer gave rise to increasing positive errors with increasing count rate; this overall positive error was composed of a positive error due to the slowness of the electronic circuitry, and a smaller negative error due to the finite pulse-width. Adequate correction could be performed by feeding the information from the dead-time output of the multi-channel analyzer to an external live-time circuit with variable oscillator frequency and pulse-width. Four methods for dead-time correction were compared experimentally in the case of short-lived radionuclides (T as low as 7 sec): the method of Bartošek et al., the method of Schonfeld, the use of a sufficiently short counting time as compared to the half-life, and the live-time mode of counting without additional correction. These four methods were applied to the determination of oxygen and silicon in rocks by 14 MeV neutron activation analysis. Results are given for USGS standard rock G-2. Research associate of the I. I. K. W.     

Error estimation of the single comparator method due to uncertainties of literature data for thermal and epithermal neutron activation cross-sections

The reliability of the single comparator method depends mainly on the accuracy of k factors. This paper describes error in theoretical k factors, especially that due to the scattering in literature data for thermal and epithermal neutron activation cross-sections. Error calculations were performed for thirteen elements using comparator sets of⁶⁰Co−¹⁹⁸Au and⁹⁵Zr−⁹⁷Zr to evaluate the accuracy of this method.     

Determination of ascorbic acid by potassium iodate

Summary Results are given for a two stage oxidation in the ascorbic acid-KIO₃ reaction under controlled conditions of acidity. The first step corresponds to the Landolt reaction and the second end point is obtained by the classical Andrews method. The reproducibility and accuracy of the results calculated on the basis of the two successive end points constitute an interesting new feature of this redox reaction involving the use of KIO₃ as a primary standard for the determination of ascorbic acid.Our sincere thanks are due to Professor S. S. Joshi for kind interest in the work and to the National Institute of Sciences of India for award of a Research Fellowship to one of us (G. S. D.).     

Application of the INAA methods for KRISS infant formula CRM analysis: standardization of INAA at KRISS

We have established an instrumental neutron activation analysis (INAA) method, including k₀-based INAA, at the Korea Research Institute of Standards and Science (KRISS) for the certification of reference materials. As part of establishing INAA measurements, KRISS infant formula certified reference material was analysed for multiple elements at three different metrological institutes: KRISS and NIST for the standard comparator method, and JSI for the k₀-INAA method. The mass fraction of most elements was consistent within expanded uncertainty (k?=?2). In addition, the results were used to verify the validity of elemental analysis of Zn using the standard comparator INAA at KRISS, and spreadsheet-based INAA calculations were evaluated.

     

Reduction of selenious acid by hydrazine sulphate. Volumetric determination of selenium

Summary A volumetric method of estimating selenium, depending upon the reduction of selenious acid by excess hydrazine sulphate solution and titration of the excess against KIO₃ to the iodine monochloride end point, has been described. Determination of tellurium on these lines is suggested.The author is indebted to Professor S. S.Joshi for facilities and kind interest in the work. The award of a Scientific Man Power Committee Research Fellowship is also gratefully acknowledged.     

Diphenylcarbazone as an internal indicator in mercurimetric analysis: The determination of cerium by potassium thiocyanate

Summary The quantitative oxidation of thiocyanate by ceric sulphate has been studied and the method utilised for the determination of small quantities of cerium by back titrating the excess (unreacted) KSCN against standard mercuric nitrate with diphenylcarbazone as the internal indicator. Accurate results are obtained under the specified experimental conditions and the procedure is more simple and direct than that adopted during earlier studies of the above redox reaction.Grateful thanks of the author are due to Professor S. S. Joshi for facilities during the work and to the National Institute of Sciences of India for award of a Research Fellowship.     

The internal comparator method

An internal comparator method is proposed which offers reliable instrumental neutron activation analysis (INAA) results for samples with an irregular geometry and/or measured at the closest position to the Ge detector. Because the selected internal comparator in the sample analyzed will receive exactly the same thermal neutron flux as the other components, this method can be applied to the INAA of materials suffering from thermal neutron self-shielding. To apply the internal comparator method, the k₀-method must be installed and the analytes, including the internal comparator, should be homogeneously distributed in the test portion.     

Fast neutron activation analysis of rare-earth elements in monazite from Korea

The relative ans single comparator methods have been applied to determine 7 rare-earth elements and U, Th in Korean Monazites by 14.5 MeV neutron activation analysis. The (n, 2n) nuclear reactions are used for all elements except La, for which (n, p) reaction is used. Al is used as a flux monitor for the relative method and as a singlle comparator for the single comparator method. The analytical results obtained by the two methods agree well within 3% deviation except for Sm and Gd. These results are also compared with the result obtained by a single comparator method using reactor neutron.     

Bestimmung von freiem und gebundenem wirksamem Chlor

Zusammenfassung Eine Untersuchung der amperometrischen Titration von Gemischen freien und gebundenen wirksamen Chlors mit Phenylarsenoxid ergab, daß die Umsetzung des freien Chlors mit Phenylarsenoxid bei pH 7 nicht vollständig abläuft. Durch Zugabe einer katalytisch wirkenden Menge Jodid wird die Reaktionshemmung aufgehoben und eine eindeutige Trennung der Bestandteile ermöglicht (Jodwellen-Methode). Mit dieser Methode als Standard für freies Chlor und der Benzidin-Pyridin-Methode, der potentiometrischen und amperometrischen Titration mit Phenylarsenoxid als Standard für Gesamtchlor wurden anschließend Testanalysen mit den bekannten differenzierenden Chlorbestimmungsverfahren vorgenommen und deren Standardabweichungen, Fehlerbereiche und Nachweisbarkeitsgrenzen errechnet. Als bestes Verfahren wurde dabei die Diäthyl-p-phenylendiamin-Methode nach Palin ermittelt. Die neutrale Orthotolidin-Methode sowie das Verfahren nach Gad wie auch dessen Verbesserung nach Lotz sind unzulänglich. Für die zur Errechnung des Gehalts an gebundenem Chlor notwendige Gesamtchlorbestimmung sind die Asmussche Benzidin-Pyridin-Methode und die potentiometrische Titration mit Phenylarsenoxid den verglichenen Verfahren weit überlegen, so daß man bei größeren Anforderungen an die Meßgenauigkeit sich besser zweier Verfahren bedient.

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Summary An investigation of the amperometric titration of mixtures of free and combined effective chlorine with phenylarsenic oxide revealed that the reaction of free chlorine with the reagent at pH 7 is not complete. By addition of a catalytically active quantity of iodine the inhibition of the reaction is released and a clear separation of the components is made possible (iodine-wave method). By means of this method as standard for free chlorine and of the benzidine-pyridine method, the potentiometric and amperometric titration with phenylarsenic oxide as standard for total chlorine test determinations have been carried out with the known differentiating methods for chlorine determination and their standard deviations, ranges of error and limits of detection have been calculated. The diethyl-p-phenylene diamine method by Palin has been found to be the best one. The neutral ortho-tolidine method as well as the procedure according to Gad and its improvement by Lotz proved to be insufficient. For the determination of total chlorine necessary for the calculation of combined chlorine the benzidine-pyridine method of Asmus and the potentiometric titration with phenylarsenic oxide are by far superior to the other methods. Therefore, it is recommendable to apply two methods if higher accuracy is required.

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Für die Durchführung der sehr umfangreichen analytischen Arbeit sage ich den Damen M.-L. List und J. Zappe meinen herzlichen Dank.     

Secondary structure elements in polylactic acid models

Geometry optimization results are reported on putative elements of secondary structure in decameric units of polylactic acid (PLA) analogous to those seen in protein structure—helical structures (α, π, 3₁₀) as well as a β-sheet—employing molecular mechanics, semiempirical, ab initio and density functional methods. The four possible structures of the deca-PLA are generally predicted, with all methods to be within ~15 kcal/mol of each other, with the more stable conformation varying depending on the method employed. The highest-level method employed here (M062x/6-311+G**) predicts that the α, π and 3₁₀ structures have very similar energies, with π slightly favored by values within the error limits of the method; this is in contrast with results obtained with less accurate semiempirical and empirical methods, which predict larger differences and other structures as favorites. Relative energies of poly-l and poly-d,l lactic acid structures indicate the former to be energetically-favored over the latter. Three types of weak interactions appear to dictate the relative stabilities of secondary structure elements in polylactic acid structures.     

Iodine monochloride end point in the oxidation of thiocyanate by permanganate. Determination of cerium

Summary A new volumetric method for cerium determination based on the quantitative reduction of Ce(SO₄)₂ by excess potassium thiocyanate and titration of the excess with standard KMnO₄ to the ICl end point has been described.Sincere thanks of the authors are due to Professor S. S. Joshi for facilities and kind interest in the work. The award of a U. P. Scientific Research Committee Scholarship to one of us (M.K.J.) is also gratefully acknowledged.     

Computer estimation of dissociation constants. Part IV. Precision and accuracy of potentiometric determinations

The protonation constants logK _Hj of the acidH _J are determined by regression analysis of potentiometric titration data whencommon parameters (logK _Hj,j = 1,...,J) andgroup parameters (E ⁰,L ₀,H _T ) are refined. Two kinds of systematic error have been investigated: the error from an uncertainty of group parameters and the error from a computational strategy of the minimization algorithm used. An analysis of variance of logK _Hj matrix was made for 6 reproduced titrations and 7 computational strategies of 6 various regression programs. It was concluded that the influence of the program used is negligible. From two ways of calibration of the glass electrode cell,the internal calibration (performed during titration) was slightly more accurate thanthe external calibration (done separately). Of programs tested, the ESAB and ACBA are most powerful because they permit refinement of group parameters and internal calibration. D-tartaric acid was chosen as model substance.Previous Part III.: Iraqi J. Sci.1981,22, 67.     

Analytical aspects of some organic acids

Summary Back titrimetric procedures for the estimation of aluminium, zirconium, and thorium have been developed, which involved the adjustment of the concentration of the metallic salts, concentration of EDTA,ph, and temperature, addition of indicator solution (namely, 2-hydroxy3-naphthoic acid and back titration with standard 0.1 M ferric chloride solution. This method is based on the fact that the excess EDTA, which is added to the metal solutions may be back titrated with iron(III), which forms a highly coloured complex with the indicator, when present in slight excess. Quantities of aluminium, zirconium and thorium as small as 10.8, 4.6, 11.6 mg respectively, can be back titrated with in experimental error, when present in a volume of 100 ml.Part IV: See Z. analyt. Chem. 172, 356 (1960).     

Activation analysis of geological material using ruthenium as a multiisotopic comparator

The isotopes⁹⁷Ru,¹⁰³Ru and¹⁰⁵Ru, produced by reactor irradiation of elemental ruthenium, were applied as triple comparators in the activation analysis of rock FU-41, a basanitoid from Fuerteventura, Canary Island. The concentrations of the following elements were determined: Sm, Sc, Fe, Co, Na, La, Hf, Eu, Th and Cr. The aim of this work was the experimental control of the error theory of the multiple comparator method as well as the experimental check of the accuracy. Presented at the 3rd Symposium on the Recent Developments in Neutron Activation Analysis, Cambridge (U.K.), 2–4 July 1973.