Evaluation of some X-rays and low energy gamma-rays in instrumental neutron activation analysis

The dependence of self-absorption of X-rays and low energy -rays on energy and sample matrix has been studied for^94mNb,¹²⁸I,^104mRh,²³⁹U and²³³Th. Experimentally determined attenuation factors have been compared to calculated values. The use of these nuclides in the instrumental neutron activation of practical samples has been evaluated.     

Study of gamma-photon self-absorption in stainless steel samples by experimental and calculational methods

Gamma-ray self-absorption in stainless steel samples has been studied with an experimental method based on fast neutron activation and a Monte Carlo calculation technique adapted to the experimental conditions. A relation between self-absorption and absorption of -photons inside stainless steel samples was found. The influence of the -ray energy and sample depth have been investigated. Agreement between the two methods has been found.     

Nondestructive determination of lead-210 and radium-226 in sediments by direct photon analysis

A method is described for the non-destructive determination of²¹⁰Pb and²²⁶Ra in sediments. The procedure is based on the direct counting of the 46.5-keV -ray of²¹⁰Pb and the 351.9-keV -emission of²¹⁴Pb. The self-absorption of the 46.5-KeV -ray is corrected using a technique involving direct gamma transmission measurements on sample and efficiency calibration standard. Several reference materials when assayed by the described method yielded results in general agreement with the certified values. The application of the method is illustrated through the analysis of the excess²¹⁰Pb profile of a Lake Ontario sediment core.     

A practical approach for self-absorption correction in210Pb gamma-spectrometric dating

Self-absorption correction of low-energy (<100 keV) -radiation is a much debated subject when applying low-energy -rays for dating purposes. Some investigations have hitherto focused on the possibility of using either irradiating of the sample and subsequent absortiometry or introducing physical correction. In the present paper an automatic procedure was elaborated using the occurrences of other low-energy -lines in the sample, those of²³⁴Th. Theoretical considerations are described on the basis of the mass absorption coefficients as a function of energy and atomic number. These considerations are verified by experiments with rock forming oxides and carbonates mixed with Standard Reference Material. Finally, an example is given for the application of the self-absorption correction approach.     

Multielement analysis of archaic Chinese bronze and antique coins by fast neutron activation analysis

Samples of archaic bronze have been investigated by fast neutron activation analysis using both the absolute and relative method. The components Cu, Zn, Sn and Pb have been determined quantitatively. For the detection of lead via the short-lived isomeric state^207mPb, cyclic activation and measurement technique was used with pneumatic sample transfer between detector and central irradiation position of the neutron tube. For nondestructive analysis of antique Chinese coins the samples had to be irradiated outside the neutron generator KORONA. The activation reactions, the evaluation of the elemental concentrations and the accuracy of the results are discussed. The data were corrected for -ray self-absorption in the samples and summing of coincident -rays in the detector. According to reported typical compositions of Chinese bronze from different dynasties, the age of the samples has been derived from the results obtained.     

Composite absorbers of inorganic ion-exchangers and polyacrylonitrile binding matrix

Maximum attainable self-absorption dose for cemented composite ion-exchanger, consisting of nickel hexacyanoferrate and polyacrylonitrile binding matrix, loaded with¹³⁷Cs up to repository acceptable level (1.1·10¹² Bq·m^–3) was calculated to be 10⁵ Gy. The cemented absorber with sorbed caesium was irradiated by⁶⁰Co source up to 1 MGy, and leach tests were performed to determine possible influence of self-irradiation on the caesium leachability. No radiation induced changes in caesium immobilisation in solidified ion-exchanger were observed.     

Rapid determination of90Sr by Compton suppression gamma-ray spectrometry

This work presents a low-level background gamma spectrometry system capable of achieving rapid determination of⁹⁰Sr without chemical separation, in a soil sample when the⁹⁰Sr to -ray emitting nuclide concentration ratio exceeds 10. The system consists of a highly efficient HPGe central detector operated in coincidence or anticoincidence with a NaI(Tl) guard detector and a NaI(Tl) backscatter detector. Experimental results indicate that the bremstrahlung radiation from a pure -emitter can be distinguished with respect to the differences in normal and coincidence spectra. The⁹⁰Sr activity can be directly detemined in the sample in less than 1 hour with a minimum detectable concentration (MDC) estimated at 0.002 Bq·g^–1 for a sample containing no appreciable -ray nuclides or other high energy, -emitting nuclides. In actual measurement, a 0.06 Bq·g^–1 MDC for contaminated soils is achieved.     

Development of90Sr/90Y (β) surface applicators by powder metallurgical technology

In recent years, -particle surface applicators (such as³²P,⁹⁰Sr) have been widely used in treating some diseases of dermotology, ophthalmology, otolaryngology etc. in China. The powder metallurgy and metal rolling technology of strontium-90/yttrium-90 () sources and the manufacture process of⁹⁰Sr/⁹⁰Y surface applicators are described in this paper. For this kind of radioactive sources, the strontium-90 insoluble compound is incorporated in a silver matrix which is sandwiched between the gold (or silver) face and the silver backing. The external surface of strontium-90 foil source is then protected by palladium or tungsten-nickel alloy coating. The characteristics of strontium-90 surface applicator are of uniform dose rate, small self-absorption and safety in use, so it can satisfy the requests of medical care.     

K β /K α X-ray intensity ratio in the region of 15≤Z≤22

The X-ray intensity ratioK /K has been measured by using a 10 mCi⁵⁵Fe source (MnK X-rays) and high resolution Si(Li) detector system coupled to a computer-controlled multichannel analyzer over the range of 15Z22. Corrections have been made to the measured relative intensities (K andK X-rays) for self-absorption in the sample, air, Be-window absorption and detection efficiency. The results are compared with those of other experiments and with the Scofield calculations.     

Activation analysis of129I

Different methods (-, - and X-ray spectrometry, activation analysis, mass spectrometry) are reviewed for¹²⁹I determination in environmental samples. The sensitivities and the¹²⁹I/¹²⁷I ratios of the different methods are given. The influence of the¹²⁷I(n, )¹²⁸I(n, )¹²⁹I(n, )¹³⁰I reactions on¹²⁹I determination by activation analysis has been studied. A chart of optimal sample irradiation conditions is given.     

The Corrected Value of the Y La Mass Absorption Coefficient in Silicon

In earlier experiments some irregular effects were observed in the X-ray spectra of yttrium doped -sialon ceramics. Yttrium L was totally absorbed whereas yttrium K was present in the spectra. Since the only reasonable explanation for these observations seems to be the effect of the silicon K-absorption edge on the entire absorption of the Y L, the experimental determination of the Y L mass absorption coefficient (mac) in silicon was performed. The silicon layer has been deposited by thermal vacuum evaporation simultaneously on the surfaces of the silica glass plate, the nickel plate and on the polished surface of the yttrium oxide sample. The silicon-covered silica glass plate was used for the layer thickness measurements (interference microscope). The silicon layer on the nickel plate was employed in the measurements of the Ni L mac value in silicon in order to verify the correctness and accuracy of the methodology. The yttrium L intensities were then measured at the silicon covered and uncovered parts of the yttrium oxide sample surface. The measured intensities were corrected with respect to the primary electron backscattering in silicon and their energy reduction in the layer. Typical EPMA instrumentation was used in all measurements. The value of the yttrium L mass absorption coefficient in silicon computed on the basis of the Lambert-Beer law appeared to be not lower than 7100 [cm²g^–1] against the value of about 3255 [cm²g^–1] reported in X-ray tables.     

Kinetic Determination of Microquantities of Rutin by Perturbation of the Bray-Liebhafsky Oscillatory Reaction in an Open System

A kinetic method is described for the microquantitative (microconcentration/microvolume) determination of rutin based on potentiometric monitoring of the concentration perturbations of the Bray-Liebhafsky (BL) oscillatory reaction being in a non-equilibrium stationary state close to a bifurcation point. The experiments are carried out in an open reactor. The response of the matrix system to perturbations by different concentrations of rutin ethanolic solutions is followed by a Pt-electrode. In the concentration range between 7.8×10^–8moldm^–3 and 9.1×10^–6mol dm^–3, we found a linear dependence of the maximal potential shift, E_m, on the logarithm of the rutin concentrations. The unknown concentrations can be determined from the calibration curve up to an accuracy of ±5%. The detection limit is 3.6×10^–8mol dm^–3. The amount of required sample can be as small as 10µL.     

Solid Phase Extraction of Molybdenum on Modified Octadecyl Silica Sorbents in the Presence of Cationic Surfactants and on Silica-Based Anionic Exchanger and its Determination by Inductively Coupled Plasma Emission Spectrometry

Molybdenum was separated and preconcentrated as molybdate on microcolumns of octadecyl silica sorbents and silica-based strongly basic anion exchanger prior to its determination by ICP-AES. With octadecyl silica Separon SGX C18 and Separon SGX RPS, the retention of 0.01–0.4µg·mL^–1 Mo from 50–1000mL sample solutions was quantitative in the presence of the cationic surfactants carbethoxypentadecyltrimethylammonium bromide (Septonex^®), dodecylbenzyldimethylammonium bromide (Ajatin^®) or tetradecylbenzyldimethylammonium chloride (Zephyramine^®) at pH 6–8. 96% ethanol was the most suitable eluent of the molybdate/surfactant associate. For the strongly basic anion exchanger Separon SGX AX, the optimal conditions for sorption of 5–20µg Mo from 50–250mL sample solutions were at pH 2 in the presence of 0.05M ascorbic acid and ammonium citrate. 3M HNO₃ was a satisfactory eluent in this case. Organic solvents and excess of acids were removed by evaporation prior to the determination of Mo by ICP-AES in eluates. Both procedures can be used for the determination of ion-level molybdenum in waters.     

Determination of boron in the thin surface layer of a silicon wafer by instrumental charged particle activation analysis

Instrumental charged particle activation analysis (CPAA) for determining boron in a thin surface layer of silicon was developed. The nuclear reaction and incident energy were selected in order to minimize any interference from surface or bulk impurities. Thin boron film was used as a standard sample and its boron content was determined by neutron induced prompt -ray analysis. As a result, we were able to determine¹¹B and¹⁰B at 10¹⁵ atoms/cm² with an accuracy of better than 3% by 4 MeV proton and 7 MeV -bombardment, respectively. Each boron isotope could be determined down to 10¹³ atoms/cm². Our CPAA was applied to determine boron in a boron implanted silicon wafer of a SIMS standard sample.     

Application of the double ratio technique to emulsion systems for liquid scintillation counting of3H and14C labelled materials

Emulsion counting, more correctly known as colloid counting, is the most widely practised technique for the radioassay of aqueous sample types by the liquid scintillation technique. The double ratio technique can be used to determine whether or not radioactivity is being counted with true solution efficiency, and was applied to a range of systems consisting of deionised water, Triton X-100 and toluene (containing³H-water,³H-toluene or¹⁴C-toluene). Some hypotheses were developed in an attempt to explain the double ratio values obtained for the various systems studied.     

Rapid radiochemical separation and determination of chlorine,bromine and iodine in water samples using ion exchange

On the basis of tracer experiments, a simple and rapid radiochemical separation method for simultaneous determination of I^–, Br^– and Cl^– in one aliquot of a water sample (only 2–4 ml) has been developed. The method is based on short irradiation of the water sample and separation of the halogens using sequential ion exchange columns filled with Dowex 1×8, 100–200 mesh anionic resin prepared in I^–/I₂, Br^–/Br₂ and Cl^– form. After washing the columns with an appropriate volume of 2% NaCl solution, the resins were transferred to vials and activities of the isolated radionuclides¹²⁸I,⁸²Br and³⁸Cl measured together with standards in a well type or on a coaxial Ge detector connected to a Canberra 90 multichannel analyzer. Besides high chemical yields, from the -spectra of the isolated radionuclides, it is evident that high decontamination fac-The paper was presented at the MTAA-8, Vienna, September 1991.     

Determination of components of the order parameter tensor of cholesteryl myristate by1H NMR data

The order parameter and orientation of the long axis of a cholesteryl myristate molecule have been determined by the second, fourth, and sixth moments of the¹H NMR line of a polycrystalline sample in the smectic phase. The effects of molecular diffusion in the cholesteric phase are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1269–1272, July, 1995.     

Spectrophotometric determination of osmium with ethylisobutrazine hydrochloride

The sheath flow cuvette is used for refractive index determinations of neat solutions within picoliter probe volumes. In this detector, a sample stream is injected as a narrow stream into the center of a flowing sheath stream under laminar flow conditions. The sample stream retains its identity as a thin cylinder through the center of a 250-m square flow chamber. The propagation properties of a focused helium-neon laser are perturbed by interaction with the sample stream. Detection limits of RI=3×10^–6 were obtained within a 20 micrometer radius sample stream, corresponding to about a 400 picoliter probe volume. For analyte with refractive index significantly different than the solvent, detection limits are possible which correspond to a few picograms of analyte within the probe volume.     

Proton induced X-ray emission (PIXE) analysis on thick samples exemplified on the rare earth elements

Summary A semiempirical procedure is developed for the calculation of the signal intensity for thick sample PIXE experiments. The calculated X-ray intensity emerged out of a thick sample is factorized into the overall produced intensity within a thick sample and an effective transmission factor for the X-ray self-absorption.The accuracy of this procedure is limited by the reliability of the experimental input parameters to about ±25%.We find as an important result of this study: The signal intensity is calculated as a function of the various experimental parameters, i.e. proton energy and sample composition including interelement- and matrix effects. This function is presented as a closed equation, which can be applied very easily, i.e. without large scale computers, to calculate the sample elemental concentration. The mass absorption coefficient of the sample most strongly influences the effective transmission term.Enhancement corrections are calculated for additional interfering rare earth elements j. No significant interelement-effects appear at concentrations c _j 2 weight%, where analysis by PIXE may be interesting. The calculated results agree well with experimental data for the rare earth elements in different matrices.Dedicated to Karl Gleu on the occasion of his 80th birthday     

Analysis of Short-Chain Fatty Acids in Fecal Samples by Headspace-Gas Chromatography

The level of short-chain fatty acids (SCFAs) is related to health benefits. In this study, a static headspace (HS) gas chromatography method was developed and validated for analyzing SCFAs in fecal samples. SCFAs were injected onto a column through an HS injector through an HS procedure and salting-out technology. The limits of detection and quantification (LOQ) of this method are 0.02–0.08 µg L^??1 (0.4–1.6 µg g^??1 sample) and 0.005–0.020 µg L^??1 (0.1–0.4 µg g^??1 sample), respectively. The calibration curves show good linearity over the range (LOQ–200 µg L^??1 or LOQ–4000 µg g^??1 sample) of these compounds, and the correlation coefficient is >?0.99. The recovery of the method is between 80 and 105%, and matrix effects were not observed. The proposed method was successfully applied to analyze SCFAs in fecal samples from rats.

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