Design Features of a Prompt Gamma Neutron Activation Analysis System at HANARO

The design features are described of a prompt gamma neutron activation analysis system at HANARO, a 30 MW research reactor in the Korea Atomic Energy Research Institute. The beam consists of polychromatic thermal neutrons diffracted by a set of pyrolytic graphite crystals at orders n in the range 1n6 at a Bragg angle of 45° on a horizontal beam line. A neutron flux of 1.0·10⁸ n·cm^–2·s^–1 is calculated at the sample position from the reflectivity of the crystal which has been confirmed in a measurement of a diffracted neutron spectrum using a time-of-flight spectrometer and gold-wire activation. The fast neutron and gamma backgrounds will be low due to the use of a diffracted beam and a tapered collimator. The detection system comprises a 30% n-type HPGe detector, signal electronics and a fast ADC. The first application of this system will be the analysis of boron concentration in biological samples for neutron capture therapy. Construction of the beam line and the arrangement of the detection system is proceeding.     

Photorefractive Properties of Photochemically Modified Poly(hydroxyaminoether)

The exposure of photosensitive poly(hydroxyaminoether)-based polymer compositions to light leads to the formation of an image with nonlinear optical and photoelectric properties and, hence, photorefractive behavior. Using the holographic birefringence technique, it was shown that the pumping of one of laser beams (signal beam) at the expense of the intensity of another (reference beam) takes place in the photochemically modified regions of the polymer layer. Unlike the majority of the previously studied photorefractive polymeric media, the beam-coupling gain coefficient (cm^–1) exceeds the absorption coefficient (cm^–1); i.e., the intensity of the signal beam after passing the layer becomes higher than that before the layer. A net internal gain, i.e. the difference – , of 117 cm^–1is achieved at E ₀= 26 V/m. The photorefractive effect is absent from the unexposed areas of the layer.     

Three-dimensional analysis of trace elements with the CAMECA IMS 4F

Summary The CAMECA IMS 4F operates in the microprobe and microscope modes with submicron lateral resolutions. The high useful yields obtained via the appropriate primary ion beam species and high transmission ion optical system give access to trace analysis in small structures. As an example, a depth profile of arsenic in silicon performed at 5,000 mass resolution in a 8 m² area allows detection of 1.10¹⁶ at/cm³ (0.2 ppm).

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Dreidimensionale Analyse von Spurenelementen mit dem CAMECA IMS 4F

     

Depth profile studies of ZrTiN coatings by laser ablation inductively coupled plasma mass spectrometry

The feasibility of depth profiling was studied by using a 193-nm ArF* excimer laser ablation system (GeoLas, MicroLas, Goettingen, Germany) with a lens array-based beam homogenizer in combination with an ICP-QMS Agilent 7500. Two ablation cells (20 and 1.5 cm³) were compared at the laser repetition rate of 1 Hz, laser beam energy of 135 mJ and the carrier gas flow rate 1.5 L min^–1 He + 0.78 L min^–1 Ar. The ablation cell dimensions are important parameters for signal tailing; however, very small cell volumes (e.g. 1.5 cm³) may cause memory effects, which can be probably explained by dominant inertial losses of aerosol on cell walls with its delayed mobilization. The 20-cm³ ablation cell seems to be appropriate for depth profiling by continuous single-hole drilling. The study of the influence of the pit diameter magnitude on the waning and emerging signals under small crater depth/diameter aspect ratios, which range between 0.75 and 0.0375 for the 3-m-thick coatings and pit diameters 4–80 m, revealed that the steady-state signals of pure coating and pure substrate (out of interface) were obtained at crater diameters between 20 and 40 m. Depth resolution defined by means of slopes of tangents in the layer interface region depend on the pit diameter and has an optimum value between 20 and 40 m and gives 0.6 m for the 20-m pit. In-depth variation of concentration of coating constituent (Ti) was proved to be almost identical with two different laser/ICP systems.Viktor Kanický performed this work while on leave at ETH Zurich     

Kinetics and mechanism of the interaction of azide with [(H2O)(tap)2RuORu(tap)2-(H2O)]2+ ion at physiological pH

The title reaction has been studied spectrophotometrically in aqueous medium as a function of [substrate complex], [ligand], pH and temperature at constant ionic strength. At the physiological pH (7.4) the interaction with azide shows two distinct consecutive steps, i.e., it shows a non-linear dependence on the concentration of N₃ ^–; both processes are [ligand]-dependent. The rate constant for the processes are: k ₁10^–3 s^–1 and k ₂10^–5 s^–1. The activation parameters calculated from Eyring plots are: H ₁ = 14.8 ± 1 kJ mol^–1, S ₁ = –240 ± 3 J K^–1 mol^–1, H ₂ = 44.0 ± 1.5 kJ mol^–1 and S ₂ = –190 ± 4 J K^–1 mol^–1. Based on the kinetic and activation parameters an associative interchange mechanism is proposed for the interaction process. From the temperature dependence of the outersphere association equilibrium constant, the thermodynamic parameters calculated are: H ₁ ⁰ = 4.4 ± 0.9 kJ mol^–1, S ₁ ⁰ = 64 ± 3 J K^–1 mol^–1 and H ₂ ⁰ = 14.2 ± 2.9 kJ mol^–1, S ₂ ⁰ = 90 ± 9 J K^–1 mol^–1, which gives a negative G ⁰ value at all temperatures studied, supporting the spontaneous formation of an outersphere association complex.     

Depth Profile Analysis on the Nanometer Scale by a Combination of Electron Probe Microanalysis (EPMA) and Focused Ion Beam Specimen Preparation (FIB)

Electron probe microanalysis (EPMA) offers high sensitivity and high accuracy in quantitative measurements of chemical compositions and mass coverages. Owing to the low detection limits of the wavelength-dispersive technique, monolayers with mass coverages of about 0.05µgcm^–2 can be detected. Assuming a density of 5gcm^–3 this corresponds to a thickness of 0.1nm. With these advantages in mind, EPMA was extended to depth profile analysis in the sub-micron range using a surface removal technique.The present paper shows how depth profile analysis can be improved by combining EPMA and the focused ion beam (FIB) technique. The focused ion beam system uses a Ga⁺ ion beam. The ion beam allows the milling of defined geometries on the nanometer scale, so that very shallow bevels with exactly defined angles in relation to the surface can be obtained. Low surface damage is expected due to low sputtering effects. Calibrated WDX measurements along the bevel deliver quantitative concentration depth profiles. First results obtained with this new combination of methods will be presented for a multilayered sample used in optical data storage.     

Radiochemistry of germanium

Since the publication ofRadiochemistry of Germanium (NAS-NS-3043) in 1961, there have been significant developments on the subject. During the period from 1970 to 1980, the diagnostic utilization of the⁶⁸Ge⁶⁸Ga generator system in nuclear medicine stimulated research in the field. In addition, over the past 30 years there have been many advances in the analytical chemistry of germanium (Ge), owing to the rapid increase in application of Ge in the electronics industry and, most recently, as an important component in infrared spectrometers.This fatest review has been completely rewritten. A literature search has been completed through December of 1990. Literature for selected topics has been surveyed through September 1993. The first section contains general information about germanium and its radioisotopes, and relevant nuclear data in tabulated form. In the second section, a general review of the inorganic and analytical chemistry of Ge is presented. Following these two introductory sections, subsequent sections deal with the production and preparation of germanium radioisotopes, separation and determination of Ge, of particular interest to the radiochemist, and selected procedures for its determination in or separation from various media. The section on separation chemistry has been greatly expanded.The review includes sections on hot-atom chemistry and the chemical behavior of carrier-free⁶⁸Ge. A section entitled Applied Radiochemistry of Germanium deals specifically with⁶⁸Ge⁶⁸Ga generator systems, the role of⁷¹Ge in the detection of solar netrinos, and the preparation of⁶⁸Ge positron sources for studying dislocations in metallic lattices and calibration of Positron Emission Tomography (PET) cameras.Two other noteworthy points follow. Throughout the text, the oxidation state of a metal ion having only one stable state, such as germanium, is not explicitly indicated. Therefore, Ge typically represents Ge⁴⁺. Other ions such as arsenic and tin, however, are indicated with their appropriate oxidation states. The term carrier-free applies to radioactive preparations to which no isotopic carrier (stable isotopes) is intentionally added.     

A fluorescence detection system for the analytical ultracentrifuge and its application to proteins,nucleic acids,and viruses

A fluorescence detection system was developed for the analytical ultracentrifuge Spinco model E. Fluorescence is excited by a laser beam which is focussed into the cell and illuminates an area with a dimension of 60 m in radial direction. For scanning the laser beam is moved in radial direction. After passing the cell, the laser beam is quenched by a carbon light trap and a set of optical filters. Fluorescence emission intensity is monitored by a photomultiplier located behind the light trap and the set of filters. The sensitivity of the detection system was tested by applying it to the sedimentation analysis of proteins and nucleic acids. Bovine serum albumin (BSA) was covalently labelled with the fluorescence-dye fluorescein-isothiocyanate (FITC), and its sedimentation coefficient could be determined even if BSA was analyzed in a concentration as low as 10^–10 M. Nucleic acids were labelled non-covalently by the intercalating dye ethidium bromide. Only 8 ng RNA were needed for the determination of the sedimentation coefficient. The particular advantages of the fluorescence detection system were exploited for the establishment of a new method for quantitative virus detection. To tobacco mosaic virus (TMV) a monoclonal anti-TMV antibody from mouse was bound, and to this a second, anti-mouse antibody that carried the fluorescence-label FITC was attached. Either by UV-irradiation or by incubation with glutaraldehyde, the first antibody was covalently crosslinked to TMV, and the second antibody to the first. In CsCl density centrifugation with fluorescence detection as little as 3.2 ng virus/80 l or 6×10⁸ virus particles/ml were recorded in a well expressed band at the corresponding buoyant density. Tenfold lower concentration would result still in a significant band. The sensitivity compares well with those of the most advanced techniques from immunology. Due to the specific labelling of viruses by antibodies it will be possible to carry out quantitative physical characterization of virus containing samples without purifying the virus. Future applications of the fluorescence detection system and of the virus detection technique are discussed.This paper was presented at the VI. Symposium on Analytical Ultracentrifugation, Marburg, FRG, February 16–17, 1989.     

Method comparison study on soot-selective techniques

In a long-term field study at two locations with different air pollution levels several soot-selective measurement techniques were compared with a thermochemical method which measures non-extractable carbon (NEC) detecting the evolved CO₂ by means of coulometric titration. The attenuation measurement technique (aethalometer) and the aerosol photoemission method showed good correlations to NEC for concentrations ranging from 1.6g/m³ to 40.8g/m³. The specific mass absorption coefficient of black carbon with respect to NEC varied between 8.4m²/g and 13.7m²/g with respect to the measurement sites, but the value was found to remain constant at each site independent of seasonal or meteorological variations. The ratio of photoelectric signal to NEC varied between 16 fA·(g/m³)^–1 and 33 fA·(g/m³)^–1 depending on the age of the aerosol. The diurnal variations of that ratio showed strong similarities to the traffic patterns. Additionally a slight temperature dependence of this ratio was found for the aged aerosol with a proportionality factor of – 0.35 fA·(K·g/m³)^–1. With the reflectance measurement technique (smoke shade method) reliable NEC determination was not possible for NEC concentrations 5 g/m³.     

Comparison of collinear and transverse photothermal deflection spectroscopy for trace analysis of pesticides in water

Summary A fiber optic modified photothermal deflection spectrometer (PTDS) was developed and tested for trace analysis of pesticides in water. A UV argon laser beam (=363.8 nm) was delivered to a sample cuvette either directly, or through a multimode optical fiber of 400 m core diameter. The HeNe-probe laser beam was guided to the same sample cuvette by a monomode optical fiber of 5 m core diameter and focussed not only transverse within an angle of 90°, but also collinear within an angle of approximately 0° to the Ar⁺-excitation beam. In transverse dual beam experiments a limit of detection (LOD) of 400 ppt for the pesticide DNOC (4,6-dinitroorthocresol) was achieved. The LODs for 2,4-dinitrophenol, dinoseb and dinosebacetate were 2 ppb, 18 pbb and 6 ppb, respectively. These LODs obtained with the transverse PTDS are up to 2 orders of magnitudes lower than the values taken with the Cary 2400 spectrophotometer. In collinear PTDS experiments with the pesticide dinosebacetate the enhancement factor of the LOD is about 4, when compared to the transverse PTDS using 1×1 cm² diameter sample cuvettes.     

Experimental and theoretical considerations on the calibration factor K between α-activity concentration and track density for application in radon dosimetry

This paper describes a new version of the measurement of the calibration factor, K, between radon activity concentration and track density. The use of Solid State Nuclear Track Detectors (SSNTDs) is one of the most convenient techniques to assess the radiation level of -activities in the environment. Exposed plastic films are chemically and electrochemically etched in an alkali solution and the -tracks are evaluated under an optical microscope. The detailed procedure for this study and the caliabration of the etched films for conversion of track density to radon exposure in (Bq·m^–3) are given in this paper. It was found the experimental and theoretical values of K were 1.37 and 1.27 (track·cm^–2·kBq^–1·h^–1·m³), respectively, for plastic detectors CR-39.     

Reversible Optical Sensor Membrane for Hydrogen Peroxide Using an Immobilized Fluorescent Probe,and its Application to a Glucose Biosensor

An optical sensor for hydrogen peroxide (HP) based on the probe europium tetracycline (EuTc) incorporated into a polyacrylonitrile-co-polyacrylamide polymer matrix is described. Upon optical excitation with 400-nm light, the EuTc in the membrane displays fairly strong fluorescence peaking at 616nm. The fluorescence intensity increases up to 3-fold if the sensor is exposed to solutions containing HP. The effect is reversible and can thus be used for continuous sensing. The largest signal changes with HP are observed at pH levels between 6.5 and 7.5, and the range of the response is between 10 and 300ppm (w/w) of HP, equal to 0.3 to 10mmolL^–1). At concentrations above 0.3% of HP, decomposition of the EuTc in the membrane is observed. The limit of detection is 15ppm (0.45mmolL^–1). The response is fully reversible and rather slow (10min) in both directions, but the reverse response may be accelerated by addition of a reducing agent such as thiosulfate. Alkali ions and most anions remain inert, but phosphate and citrate interfere, as do Cu²⁺ ions, which quench fluorescence. In order to image the spatial distribution of HP concentrations, sensor membranes were placed on the bottom of the wells of a microtiter plate, and their fluorescence was imaged using an LED-based device based on the measurement of the luminescence decay time of EuTc. If glucose oxidase is immobilized on the sensor layer, a glucose sensor is obtained in which the HP sensor acts as the transducer and which can quantify glucose in concentrations between 0.1 and 5mmolL^–1. The limit of detection for glucose is 0.2mmolL^–1.     

Ion-exchange equilibria of metal ions and hydrogen ions on anilinium tin(IV) phosphate

Summary Ion-exchange equilibria of metal ions (Mn^II, Cu^II, Zn^II, Cd^II and Hg^II)/H⁺ systems have been studied at 30, 40, 50 and 60°C on anilinium tin(IV) phosphate (ATP) as a cation exchanger. The exchange isotherms were measured for both forward and reverse reactions with a solution of ionic strength 0.1 by the batch technique. The isotherms are S-shaped for each ion-exchange system. Selectivity coefficients vary linearly with the equivalent fraction of transition metal ion in the exchanger in the range from 0 to 0.6. The selectivity sequence of zero loading is: Zn^II <Mn^II<Cu^II<Cd^II<Hg^II. Overall and hypothetical (zero loading) thermodynamic data are evaluated.     

Capillary neutron optics for prompt-gamma activation analysis

A neutron lens has been constructed to focus cold neutrons from the exit of a⁵⁸Ni neutron guide, which delivers a beam to the Prompt-Gamma Activation Analysis (PGAA) station at the NIST Cold Neutron Research Facility. The lens compresses a neutron beam of cross section 50 mm× 45 mm onto a focal spot of diameter 0.53 mm (fwhm) wich an average gain of 80 in neutron current density. PGAA measurements have been performed to demonstrate the enhanced sensitivity and detection limits for various elements and the spatial resolution in one transverse dimension. For the two test particles (a gadolinium glass bead and cadmium metal of sizes less than 0.5 mm), the gain in the -count rate with the lens is a factor of 60, and the detection limit is improved by a factor of 20. The system can be used for two-dimensional mapping of samples on a sub-millimeter scale to complement other analytical techniques such as neutron depth profiling (NDP).     

A method for measuring cross sections for electron-impact excitation out of metastable levels of atoms

A method for measuring cross sections for electron-impact excitation out of the metastable levels of the He atom is described. A hollow cathode discharge is used to produce an atomic beam consisting of ground-level He atoms and the He(2¹S) and He(2³S) metastable atoms. An electron beam of energy below 20 eV crosses the atomic beam exciting the metastable atoms to higher levels, and the intensity of the radiation emitted by atoms in these higher levels is utilized to determine the cross sections. Because of the very low concentration of metastable atoms in the atomic beam, the emission signal is extremely weak. A number of special techniques have been developed to detect these very low-level signals. Absolute calibration of the cross section is accomplished by referencing the emission signal that resulted from electron excitation out of the metastable level to the emission signal that resulted from the 2³S3³P or 2¹S3¹P laser optical absorption.     

Ein Projektionsversuch zur Demonstration elektrolytischer Reaktionen

Zusammenfassung Es wird gezeigt, wie man Elektrolysen auf elektronenmikroskopischen Präparatträgern mit einem für das Lichtmikroskop entwickelten Objektträger ausführt und welche Voraussetzungen erfüllt sein müssen, um durch lichtmikroskopische Projektion die Abscheidung des Niederschlages während des elektrolytischen Vorganges auf einem Bildschirm beobachten zu können. Am Beispiel der Elektrolyse von 1 bis 2l einer schwefelsauren Kupfersulfatlösung mit einer Kupfermenge in der Größenordnung von 10^–8 g sieht man in einer Bildreihe lichtmikroskopischer Aufnahmen den Ablauf eines solchen Experimentes. Nach der elektrolytischen Fällung wird auch der Nachweis des abgeschiedenen Kupfers durch seine Überführung in das kristallisierte Kupferpikrolonat demonstriert.

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Summary It is shown how electrolyses may be conducted on electron microscope carriers with an object holder developed for the optical microscope and it is stated what provisions must be met so that through luminous microscopic projection the separation of the deposit can be seen on a picture screen during the electrolytic action. The course of an experiment of this kind is described by means of an example of an electrolysis of 1 to 2l of a sulfuric acid solution of copper sulfate whose copper content was about 10^–8g and seen in a series of optical microscopic photographs. Following the electrolytic deposition, the detection of the deposited copper through its conversion into crystalline copper picrolonate was also demonstrated.

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Herrn Univ.-Prof. Dr.Hans Lieb zum 80. Geburtstag gewidmet.     

Flow-injection extraction-spectrophotometric determination of permanganate with the triphenylsulphonium cation

Summary Permanganate can be determined spectrophotometrically at 548 nm after flow-injection extraction into chloroform of the ion-associate triphenylsulphonium permanganate. The carrier stream was a pH 6 buffer containing 10% (w/v) ammonium fluoride and the reagent stream was 0.10% (w/v) triphenylsulphonium chloride. The injection rate was 20 h^–1. The calibration graph is linear up to 40 g ml^–1 and the detection limit is 1.10 g ml^–1 Mn(VII), based on injection volumes of 250 l. The system has been applied to the determination of manganese in steels and a cupro-nickel alloy.     

Kratertiefenbestimmung bei spektroskopischen Methoden zur Lokal- und Dünnschichtanalyse

Summary The following methods for the determination of crater depths have been tested in the case of local and thin film analysis by spark and laser mass spectroscopy: stylus technique, refocussing of optical microscope, optical interference microscopy, oblique observation by a scanning electron microscope in connection with contamination lines or with ion beam slope cutting, weighing technique, determination of the concentration of a monitoring element having a well known depth profile.The methods mentioned complete each other in the depth interval from 0.01 to 100 m and with regard to their usefulness for local craters and scanned areas. The weighing technique is less useful because of the very low mass losses during the analysis. As a rule, depth resolution as well as accuracy of the measuring data are limited by the roughness of the crater bottom and/or by systemactic errors in the application of the measuring techniques. The results are also applicable to optical emission spectral analysis with excitation by spark, laser beam or glow discharge, as well as to dynamic SIMS.     

Spin conversion of positronium in paramagnetic solutions studied by age-momentum-correlation method

Correlated measurement of the lifetime and of the lineshape of the 511 keV annihilation radiation of positrons (age-momentum correlation, AMOC) has become a powerful tool for investigating reactions of positron or positronium in condensed matter as a function of time. The beam-based ⁺ AMOC method installed at the Stuttgart relativistic positron beam facility (E _kin ^e+ 4MeV) offers substantial advantages over the conventional E coincidence technique resulting in a fast data taking due to the unity detection efficiency of the ⁺ scintillator which provides the start signal for the lifetime measurement. In this paper the application of AMOC to positronium chemistry is illustrated by the study of spin conversion of positronium in the system methanol/HTEMPO as a function of HTEMPO (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, a paramagnetic solute) concentration. The same technique can be applied to other systems and other reactions in positronium chemistry, e. g., oxidation or complex formation.     

Surface Tension of a Liquid under the Conditions of a Fast Surface Renewal during Evaporation

A new capillary method of measuring surface tension under the conditions of a fast surface renewal due to evaporation is considered. At the highest rates reached for n-pentane and water evaporation (0.6 and 0.14 kg m^–2 s^–1, respectively), the deviations of from its equilibrium values may be explained by a change in the meniscus shape under the conditions of intense heat exchange.