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We report initial research to develop a compact and practical primary thermometer based on Doppler broadening thermometry (DBT). The DBT sensor uses an intrinsic property of thermalized atoms, namely, the Doppler width of a spectral line characteristic of the atoms being probed. The DBT sensor, being founded on a primary thermometry approach, requires no calibration or reference, and so in principle could achieve reliable long-term in-situ thermodynamic temperature measurement. Here we describe our approach and report on initial proof-of-concept investigations with alkali metal vapour cells. Our focus is to develop long-term stable thermometers based on DBT that can be used to reliably measure temperatures for long periods and in environments where sensor retrieval for re-calibration is impractical such as in nuclear waste storage facilities. [ABSTRACT FROM AUTHOR]

A positron annihilation spectroscopy (PAS) investigation of radiation-induced damage in RPV welds was conducted. Eight different materials with composition variation of Mn, Ni, Si and Cr were manufactured based on typical WWER-1000 materials. This variation was chosen to observe the potential of synergistic role of these elements on the reactor pressure vessel (RPV) degradation. Materials were irradiated at the High Flux Reactor (HFR) in Petten as a part of LYRA-10 experiment, to displacement damage of ∼ 0.1 dpa. Subsequently, the as-received and irradiated materials were studied by the means of positron annihilation spectroscopy in the laboratory of the Institute of Nuclear and Physical Engineering of the Slovak University of Technology in Bratislava. Positron Annihilation Lifetime Spectroscopy (PALS) and Coincidence Doppler Broadening Spectroscopy (CDBS) were used to analyze the microstructure of samples. The obtained analysis from both techniques showed an increased rate of positron trapping at radiation-induced vacancy clusters with increasing content of Ni, Mn and Si in the materials. [ABSTRACT FROM AUTHOR]

In this paper, an effect of thermal stress on VVER-440 reactor pressure vessel steel (15KhMFAA) was observed by non-destructive Positron Annihilation Lifetime Spectroscopy and Coincidence Doppler Broadening Spectroscopy. This steel was investigated previously in a couple of publications, but the influence of the thermal treatment was studied mostly up to 500°C. Our recent positron results from the optimization of the recovery annealing temperature published in [1] indicated that the structure is significantly changed at temperatures over 500°C, although the reason was not in charge of structural defects on which positrons are sensitive. This paper studies closer the chemical aspects of the annealing and the formation of precipitates at temperature of 550°C. The results indicated an effect of manganese and nickel on the structure surrounding structural defects which is changing during the process of the annealing. [ABSTRACT FROM AUTHOR]

A triple coincidence digital positron lifetime setup (PALS) was combined with a coincidence Doppler broadening system (CDBS) in our laboratory to handle both measurements at the same time with the same positron source. Similar commonly used setup AMOC - Age-Momentum Correlation needs time correlation between positron lifetime and positron momentum. The exact correlation from the same positron annihilation event is not possible with this setup. Two photons from positron annihilations and 1274keV photons are used in triple coincidence PALS, and another annihilation photons spread in a line perpendicular to this plane are used for CDBS. In the CDBS part, 1274keV photons are used for steady energy calibration of the spectra. Therefore, photons detected in CDBS and PALS parts are not from the same annihilation event. From a long-term stability view, the temperature, the positron source activity and the stability of the power source are correlated and can be used to determine their impact on both measurements. [ABSTRACT FROM AUTHOR]

The magnetic Barkhausen noise technique (MBN) gained its importance in material characterisation, and it is considered as powerful tool for microstructural and indirect mechanical characterisation of ferromagnetic materials. It is well known for its sensitivity to various parameters which affect the magnetic domains configuration and domain-wall pinning sites. In the present paper, we apply the MBN to investigate the microstructural modification of miniaturised specimens of martensitic T91 (Fe8Cr) steel subjected to isochronal annealing. Thin sheets sized 10x10x0.4-0.8 mm were annealed 475 °C up to 750 h. Results of MBN are discussed with respect to a complementary positron annihilation coincidence Doppler broadening spectroscopy (CDBS) characterisation. [ABSTRACT FROM AUTHOR]

Vacancy type defect profiles of Al+ implanted Semi- Insulating (SI) 6H- SiC have been obtained using low energy positron beam Doppler broadening spectroscopy measurements. Al+ ions of 400 keV with fluence 1014, 1015 and 1016 ions/cm2 have been implanted at room temperature to produce donor concentration from 1018 to 1020 Al+/cm3. The increases in S – parameter vs. positron beam energy E indicates the production of vacancies type defects by implantation. The normalized S – parameter with pristine for implanted 6H- SiC samples confirms the production of di-vacancies (for 1014 and 1015 ions/cm2) and larger voids (for 1016 ions/cm2).. [ABSTRACT FROM AUTHOR]

We have developed a new positron annihilation measurement system via electron-positron pair creation using by laser Compton scattering (LCS) gamma beam direct implantation into bulk materials at NewSUBARU synchrotron radiation facility, LASTI, University of Hyogo, Japan. LCS gamma beam is easy to control energy, and its energy is quasi-monochromatic and high directivity. These parameters are determined by laser wavelength and electron kinetic energy. In this study, maximum energy 16.9 MeV LCS gamma beam generation by Nd:YVO4 laser (wavelength 1064 nm) and circling electron (982 MeV) directly irradiated into samples for Doppler broadening measurement in an atmosphere. The gamma beam created high energetic positrons to MeV order. This measurement could be a simple setup consisting of a single HP-Ge detector, amplifier, and multi-channel analyzer. As a demonstration, we have tried to measure the Doppler broadening spectra of pure iron, electron irradiated iron and silicon by this system. [ABSTRACT FROM AUTHOR]

This work is reports the luminescent properties and positronium formation yields of the Eu(dpm)3 and Eu(dpm)3(2-pyr) complexes, where dpm = 2,2,6,6-tetramethyl-3,5-heptanedionato (dipivaloylmethanate) ion and 2-pyr = 2-pyrrodilidone. We present and discuss experimental intensity parameters of 4f-4f transitions in the Eu3+ complexes under UV excitation. Positron annihilation lifetime spectroscopy (PALS) and Doppler broadening of annihilation radiation lineshape (DBARL) measurements were also performed. It was observed that the photoluminescent properties and Ps formation yields of the complexes are related to intramolecular processes, such as a ligand-to-metal charge transfer (LMCT). The results, which strongly evidence the participation of molecular excited states in the positronium formation, were then discussed in terms of the recently proposed Ps formation mechanism, named cybotactic correlated system kinetic mechanism (CCSKM). [ABSTRACT FROM AUTHOR]

Alkaline earth (Ae = Ca, Sr and Ba) cation substituted La1-xAexFeO3 (x = 0.1, 0.2, …, 0.5) nanocrystalline samples were prepared through the normal chemical route and were characterized by X-ray diffraction. Optical absorption studies showed an increase of the band gap with increasing x in the case of Ca and Sr but a final decrease again in Ba substitution. Positron lifetime measurements indicated decrease in annihilation at the nanocrystallite surfaces and increase in the additional defects created within the nanocrystallites. Coincidence Doppler broadened spectra showed prominent peaks at pL (10−3 m0c) = 9.8 due to the annihilation of positrons with the O²-2p electrons, which implied that the predominant defects which trapped positrons were vacancies of cations and their complexes. In the Ba-substituted samples, the annihilations with the Ba2+ 4d electrons reduced the intensity of O²-2p electron annihilation with positrons. [ABSTRACT FROM AUTHOR]

Phthalocyanine and perylene are aromatic organic compounds. Metal complexes can be derived from phthalocyanine by substituting H2 in the central ring of the molecule by a metal ion. In the present work, positron annihilation spectroscopy was employed for characterization of the size distribution and local chemical environment of free volumes in perylene, phthalocyanine and its complexes with metals. The size distribution of free volumes was determined from the pick-off annihilation lifetimes of ortho-positronium. The local chemical environment of positron annihilation sites was characterized by the coincidence Doppler broadening spectroscopy. [ABSTRACT FROM AUTHOR]

Croconic acid (CA) is the first organic ferroelectric with a spontaneous polarity in bulk samples comparable to its inorganic counterparts. As a natural extension of study, ultrathin CA films (~nm scale) were investigated to reveal ferroelectric effects in films on different substrates for their fundamental and industrial significance. However, the void defect at the interface between the film and substrate is presumed to interfere with surface effects. In this work, a non-invasive technique, a slow positron beam, coupled with Doppler broadening energy spectroscopy (DBES), is applied to study the void defects within the interfacial layer between CA films and Si and SiO2 substrates. The effect of external electric field on defect formation is also investigated and an underlying mechanism is proposed. [ABSTRACT FROM AUTHOR]

The Doppler Broadening Spectroscopy (DBS) was used to measure Kapton film thickness, varied in 0.3-30 mils range, with Ge68 positron source and pure copper (Cu), nickel (Ni) or aluminum (Al) metals as targets. The linear relationship between S-parameter and Kapton thickness was found for Cu and Ni with sensitivity depending whether the film was used on one or two sides. LYS-1¹ (Layers Profile Analysis) program was applied to determine backscatter and absorption coefficients and subsequently absorption fractions for multi-layer system with “backing-target-Kapton-source” layers in symmetrical and non-symmetrical arrangements. The experimental and theoretical S-parameter values for multilayers system with varied Kapton film thickness show a good correlation, but its precision needs to be improved. The optimization plan for better sensor is presented. [ABSTRACT FROM AUTHOR]

Investigation of zirconia nanopowders, doped with metal cations of different valence (Mg2+, Ce4+), and ceramics, obtained by sintering these nanopowders, will be reported. The nanopowders were prepared by the co-precipitation method. The Doppler broadening (DB) measurements were carried out using a slow-positron beam and combined with the conventional positron lifetime spectroscopy and electron microscopy. Nano- and mesopore data, obtained in this study, suggest that small agglomerates of nanoparticles occurs in the pressure-compacted zirconia nanopowder doped with Mg2+ cation, while only relatively small nanopores seem to be contained in the nanopowder of ZrO2, doped with Ce4+, after pressure compaction, indicating thus an absence of significant nanoparticle agglomeration in this system. [ABSTRACT FROM AUTHOR]

Software that allows fitting positron lifetime (LT) and coincidence Doppler broadened (CDB) positron annihilation spectra of nanodispersed dielectric powders is developed. Computer program takes into account following effects: possibility of e+ trapping by vacancy-type defects, formation of the surface-bound e+ states, formation and thermalization of Ps atoms in inter-granular space. In order to test the developed software, lifetime and coincident Doppler broadened spectra of Al2O3 nanopowders with different grain sizes are acquired. Suggested physical model of the processes involved gives self-consistent interpretation of the spectra. Parameters of the thermalization kinetics of Ps and its ortho-para conversion due to presence of O2 molecules adsorbed on the crystallite surface are obtained. [ABSTRACT FROM AUTHOR]

Magnetism of Gadolinium-doped gallium nitride (GaGdN) depending on the Ga flux during crystal growth is investigated using magnetic Doppler broadening (MDB) measurements and M-H measurements. In Ga deficient condition, the matrix phase of GaGdN layer is regarded as GaN due to the precipitation of GdN nanoparticles. From the MDB measurements, magnetic moments at gallium vacancies (VGa) in GaN is detected, however, ferromagnetism derived from GdN nanoparticle is dominant. In Ga rich condition, pure GaGdN layer was formed and weak ferromagnetism was observed. The MDB measurements detect the magnetic moments at VGa in GaGdN, which might be a source of magnetism. [ABSTRACT FROM AUTHOR]

A new combined positron annihilation lifetime spectroscopy (PALS) and coincidence Doppler broadening (CDB) system has been constructed at Idaho National Laboratory (INL). The design and commissioning process are discussed with practical guidelines that can be followed for the installation of new systems. In addition, the new system was used to investigate defect structure in titanium and titanium deuteride samples where the deuterium concentration ranges from 0.10 to 2 x 10-5. The TiD samples were found to be largely defect free based on the positron lifetimes and SW curves. Ratio curves of the CDB spectra showed elemental sensitivity to the deuterium in the samples, that increased with deuterium concentration. [ABSTRACT FROM AUTHOR]

We present Doppler broadened gamma spectra, obtained using the newly developed advanced positron beam at the University of Texas at Arlington, from a sample consisting of 6 to 8 layers of graphene (MLG) on polycrystalline Cu. The kinetic energy of the positron beam was varied form 2 eV to 20 keV allowing for a depth resolved measurement. The ratio curves formed by dividing the measured Doppler broadened gamma spectra obtained at low positron kinetic energies (~2eV) to the gamma spectra obtained at 20 keV were compared to ratio curves found by dividing the calculated spectra of bulk graphite to bulk Cu. The ratio curves obtained from the measured results show qualitative agreement with those obtained from the calculated spectra. In particular, both sets of curves indicate a much reduced intensity at high momentum. The agreement between the measured and calculated curves is consistent with the hypothesis that the 2eV spectra correspond to the Doppler broadened spectra from the thin overlayer of Graphene (which we anticipate should be similar to the spectra obtained from bulk graphite) and that the spectra taken at 20 keV corresponds to bulk Cu due to the fact that most of the positrons implanted at this energy annihilate in the Cu substrate. The results taken at 2 eV provide evidence that it is possible to obtain chemically sensitive information from the top atomic layers of surfaces (both internal and external) from an analysis of the high momentum tail of the Doppler broadened gamma spectra obtained from the annihilation of positrons at the surface. [ABSTRACT FROM AUTHOR]

A slow positron facility is being built in Israel, at the Hebrew University, for basic and applied research. It consists of a slow positron beam and a compact Positrons Annihilation Lifetime (PAL) spectrometer. The slow positron beam follows a traditional design, using a 22Na source, of about 40mCi, a Tungsten moderator and a unique grounded target cell, with positrons energy that can vary between 0.03 keV and 30 keV. The detection system will be comprised of High Purity Germanium and BaF2 detectors, facing each other, for low background Doppler Broadening (DB) measurements. The target cell is designed to allow a combined measurement of sample conductivity and DB, with the flexibility to add more detection options in the future. The compact PAL spectrometer includes two fast scintillation detectors read by a fast digitizer (DRS4), with a sampling rate of 5.12 GS/s. A dedicated software package was developed to emulate analogue data acquisition. Lifetime measurements were performed using a ∼25 µCi 22Na source. The time resolution was defined using a 60Co source, to be 180-200ps. First positron lifetime validation measurements of Ti resulted in positrons lifetime of 157 ± 4 ps, consistent with previously published values. [ABSTRACT FROM AUTHOR]

We developed a new scanning positron microbeam for spatially resolved (coincident) Doppler broadening spectroscopy ((C)DBS) at the neutron induced positron source Munich (NEPOMUC). For this purpose, positrons are moderated three times: First, positrons generated by pair production are self-moderated in annealed polycrystalline Pt foils inside the beam tube housing the positron source NEPOMUC. Then, the brightness of the primary 1 keV positron beam with 109 moderated positrons per second is enhanced by a W(100) single crystal remoderator operated in back reflection geometry. Finally, in the upgraded CDB spectrometer we apply a 100 nm thin Ni(100) foil acting as transmission remoderator to generate a positron microbeam with a minimum beam diameter of 33 µm. We demonstrate the potential of laterally resolved DBS by imaging the defect distribution around a laser beam weld of the high-strength age-hardenable Al alloy AlCu6Mn. CDBS was applied with unprecedented spatial resolution to reveal the dissolution of Cu rich precipitates and the formation of Al-vacancy-Cu-complexes. [ABSTRACT FROM AUTHOR]

The so-called “RPV Model Steels”, represented by 12 ferritic steels with the parametric variation of alloying elements were developed at EC - JRC Petten (the Netherlands). Their composition was derived from compositions typical for WWER-1000 and PWR RPW materials. In order to understand the role and influence of certain alloying elements and impurities on the behavior of steels during operation of NPP, the set of RPV Model Steels was irradiated in the High Flux Reactor -LYRA irradiation facility (Petten, the Netherlands) up to a neutron fluence of about 2.5×1019 n.cm-2. In this paper, we present the detailed analyses of DBS (Doppler Broadening spectroscopy) results obtained on an unirradiated set of RPV model steels. [ABSTRACT FROM AUTHOR]

Combining such methods of plasma registration as spectral, probe and optical diagnostics, in this paper propagation of laser plasma in a vacuum magnetic field was studied. By means of Langmuir and magnetic probes such plasma parameters as velocity and the angle of expansion were measured, as well as the size of magnetic cavity. Using optical monochromator combined with CCD a Doppler broadening of a number of ionic and atomic lines was measured and the transversal speed of the plasma cloud expansion was calculated. The data plasma cloud propagation velocity and expansion angle obtained by two methods was compared with gated imaging data and magnetic probe measurements of cavity size. [ABSTRACT FROM AUTHOR]

A large spectrum of ferritic steels with parametric variation of alloying elements were developed at EC - JRC Petten (the Netherlands) in order to understand the role and influence of Ni, Si, Cr and Mo as alloying elements and certain impurities as Cu and P on the properties of steels during irradiation. They were investigated by various nondestructive techniques in the in view of identifying the possible influence of alloying elements on material properties. In the present study we compare results of Doppler broadening annihilation spectroscopy and magnetic Barkhausen noise obtained on as-received specimens. [ABSTRACT FROM AUTHOR]

The Core Imaging X-Ray Spectrometer (CIXS) will be employed for measurements of the ion temperature and of the toroidal rotation velocity, Ti and vφ, respectively, as a function of the radius of ITER plasmas. The diagnostic is based on precision determinations of the Doppler broadening, centroid shift, and intensity of the lines of highly ionized heavy impurities using a curved Bragg crystal spectral disperser and imager. The ions under consideration for the diagnostic are those of tungsten, krypton, xenon, iron, and argon. A detailed discussion is given of the need for atomic physics experiments and calculations involving the primary diagnostic lines and their collisional and dielectronic satellites. Such experiments and calculations define the instrument parameters, determine the diagnostic uncertainties, and provide paths for extending the diagnostic capabilities to measure impurity concentrations, electron temperature, and ion transport parameters. Enabling the diagnostic to measure radially dependent ion transport coefficients, in particular, requires a large amount of high-quality atomic data in the form of reliable excitation, ionization, and recombination rate coefficients as well as ionization balance calculations which make use of these data. Because core imaging spectrometers are being developed and implemented on present-day magnetic fusion devices, much of the atomic data are already needed and can be tested in the analysis of existing spectra recorded by these diagnostics. [ABSTRACT FROM AUTHOR]

In this work, we study the correlation between microturbulence and nonradial pulsations of iota Herculis a B3 IV-typed star. This research is conducted using 144 spectra of iota Herculis taken from the ELODIE archive data (May 17 to 21, 1995) and 47 spectra from the archive data of Ritter Observatory (February 6, 1994 to October 30, 1995). The spectra of the ELODIE and the Ritter Observatory are analysed using the rvidlines subroutine of IRAF software to obtain the value of nonradial pulsations velocities (which represented by the heliocentric radial velocities). The heliocentric radial velocities (HRV) of iota Herculis obtained from ELODIE and Ritter Observatory are from -13.66 km s-1 to -17.09 km s-1 and -13.60 km s-1 to -29.70 km s-1, respectively. The microturbulent velocities are determined by using the important equation of the full width at half-maximum (FWHM) of the line profile for Doppler broadening. The value varies from 3.44 km s-1 to 5.32 km s-1 for the ELODIE data whereas the Ritter Observatory data are from 1.50 km s-1 to 5.83 km s-1. Both curves of HRV and microturbulent velocities show an identical pattern which the HRV curves will increase when the microturbulent velocities curves increase and vice versa. We propose the correlation between microturbulence and nonradial pulsations in this star is due to the gravity waves which drive the nonradial pulsations and subsequently induce the microturbulence. [ABSTRACT FROM AUTHOR]

In this paper, we discuss about the correlation between microturbulence and the fluctuations of central depth of S II line profile of iota Herculis a B3 IV star, based on 144 spectra from the ELODIE archive data (May 17 to 21, 1995) and 47 spectra from the archive data of Ritter Observatory (February 6, 1994 to October 30, 1995). The variations of central depth of S II line profile of this star are analyzed using the IRAF software, and the evaluations of microturbulence are determined by using the important equation of the full width at half-maximum (FWHM) of the line profile for Doppler broadening. From both datasets, we found that there is a connection between the variations of central depth of S II line profile and the microturbulence of iota Herculis. The central depth of S II line profile becomes deeper when the microturbulent velocity increases and vice versa. We propose the connection between microturbulence and the fluctuations of central depth of S II line profile in this star is due to the sub-photospheric iron convection zones (FeCZ) which have the connection with the origin of microturbulence phenomenon, stellar temperature and the opacity of this star. [ABSTRACT FROM AUTHOR]

Positron annihilation spectroscopy in Doppler broadening mode is used to study epitaxial layers of GaSb1−xBix on undoped GaSb. The samples were grown by Molecular Beam Epitaxy at different temperatures and with different Bi/Sb beam equivalent pressure ratios resulting in Bi concentrations of 0–0.7 %. The results show a relationship between the growth parameters and Doppler broadening parameters. Incorporating Bi into GaSb decreases the vacancy concentration in the epitaxial layers compared to the sample with no Bi in the epitaxial layer. [ABSTRACT FROM AUTHOR]

To provide new determinations of the Boltzmann constant, k, which has been asked for by the International Committee for Weights and Measures concerning preparative steps towards new definitions of the kilogram, the ampere, the kelvin and the mole, an iMERAPlus joint research project has coordinated the European activities in this field. In this major European research project the Boltzmann constant has been determined by various methods to support the new definition of the kelvin. The final results of the project are reviewed in this paper. Determinations of the Boltzmann constant k were achieved within the project by all three envisaged methods: acoustic gas thermometry, Doppler broadening technique, and dielectric constant gas thermometry. The results were exploited by the interdisciplinary Committee on Data for Science and Technology (CODATA) in their 2010 adjustment of recommended values for fundamental constants. As a result, the CODATA group recommended a value for k with a relative standard uncertainty about a factor of two smaller than the previous u(k)/k of 1.7×10-6. [ABSTRACT FROM AUTHOR]

The effect of triple ion beams has been investigated by simultaneous and sequential irradiations of gold, hydrogen and helium on radiation damage in the CLAM steel developed in China. The depth profile measurements of positron annihilation Doppler broadening S parameter were carried out as a function of slow-positron beam energy to examine the produced radiation damage. The experimental results show clearly the synergistic effect of displacement damage and hydrogen and helium on the formation of radiation damage. The synergistic effect of simultaneous triple ion beam irradiation of gold, hydrogen and helium ions was found to suppress the radiation damage in the CLAM steel due to the helium and/or hydrogen filling of vacancy clusters. [ABSTRACT FROM AUTHOR]

In this work we show results of Monte Carlo modeling of electrons and heavy particles induced spatially resolved emission intensity or the Doppler profile in pure H2 discharge focusing on anode boundary. In particular we present study of fast H2 and fast H particles, scattered both at the surface and of the molecules. Since the anode boundary is characterized by a large electron flux, role of electron reflection and production of secondary electrons at the anode surface is part of the complete picture of spatial emission profile. In this work we verify our models of electron backscattering from the anode including both the reflection and the secondary electron production by making comparisons with the drift tube experiments. In order to achieve consistency with our previous results we select conditions of simulation appropriate for very high E/N (E-electric field, N-gas density) that are selected from experimental Townsend discharges in pure H2. [ABSTRACT FROM AUTHOR]

The uniformity of rubber-carbon black composite materials has been investigated with positron Doppler Broadening Spectroscopy (DBS). The number of grams of carbon black (CB) mixed into one hundred grams of rubber, phr, is used to characterize a sample. A typical concentration for rubber in tires is 50 phr. The S parameter measured by DBS has been found to depend on the phr of the sample as well as the type of rubber and carbon black. The variation in carbon black concentration within a surface area of about 5 mm diameter can be measured by moving a standard Na-22 or Ge-68 positron source over an extended sample. The precision of the concentration measurement depends on the dwell time at a point on the sample. The time required to determine uniformity over an extended sample can be reduced by running with much higher counting rate than is typical in DBS and correcting for the systematic variation of S parameter with counting rate. Variation in CB concentration with mixing time at the level of about 0.5% has been observed. [ABSTRACT FROM AUTHOR]

Shot peening is a technique used in industry to increase the fatigue life of components by creating compressive residual stresses in the near surface region. This compressive stress is pinned in the material by defects such as dislocations and monovacancies to which positrons are sensitive. Using a 22Na source S-parameter measurements were made using positron annihilation spectroscopy (PAS) on both non-peened and peened copper coupons. These measurements show that a correlation exists between copper coupons shot peened at different intensities that in principal can be used for verification of shot intensity. Finally a relative defect density map was produced to show that the shot peening uniformity can also be measured across the surface of a large component. [ABSTRACT FROM AUTHOR]

Positron Annihilation Spectroscopy (PAS) techniques can be utilized as a sensitive probe of defects in materials. Studying these microscopic defects is very important for a number of industries in order to predict material failure or structural integrity. We have been developing gamma-induced pair-production techniques to produce positrons in thick samples (∼4–40 g/cm2, or ∼0.5–5 cm in steel). These techniques are called ‘Accelerator-based Gamma-induced Positron Annihilation Spectroscopy’ (AG-PAS). We have begun testing the capabilities of this technique for imaging of defect densities in thick structural materials. As a first step, a linear accelerator (LINAC) was employed to produce photon beams by stopping 15 MeV electrons in a 1 mm thick tungsten converter. The accelerator is capable of operating with 30–60 ns pulse width, up to 200 mA peak current at 1 kHz repetition rate. The highly collimated bremsstrahlung beam impinged upon our steel tensile specimens, after traveling through a 1.2 m thick concrete wall. Annihilation radiation was detected by a well-shielded and collimated high-purity germanium detector (HPGe). Conventional Doppler broadening spectrometry (DBS) was performed to determine S, W and T parameters for our samples. [ABSTRACT FROM AUTHOR]

Spectral line shapes and intensities are used for obtaining information on the various regions of magnetic fusion devices. Emission from low principal quantum numbers of hydrogen isotopes is analyzed for understanding the complex recycling mechanism. Lines emitted from high principal quantum numbers of hydrogen and helium are dominated by Stark effect, allowing an electronic density diagnostic in the divertor. Intensities of lines emitted by impurities are fitted for a better knowledge of ion transport in the confined plasma. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We present the experimental and theoretical study of the resonant excitation of rubidium and cesium atoms with fs pulse train in the conditions when the pulse repetition period is shorter than the atomic relaxation time. Velocity selective optical pumping of the ground state hyperfine levels and velocity comb-like excited state hyperfine level populations is demonstrated. Both effects are a direct consequence of the fs pulse train excitation considered in the frequency domain. A simple experimental apparatus was employed to develop a modified direct frequency comb spectroscopy which uses a fixed frequency comb for the 85,87Rb 5s 2S1/2 → 5s 2P1/2,3/2 and 133Cs 6s 2S1/2 → 6p 2P1/2,3/2 excitation, and a weak cw scanning probe laser at 780 and 852 nm for Rb and Cs ground levels population monitoring. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The presented results are concerned with the shape of Balmer alpha line emitted from a low pressure DC glow discharge with aluminum (Al) and copper (Cu) hollow cathode (HC) in pure H2 and Ar-H2 gas mixture. The analysis indicates that the line profile represents a convolution of Gaussian profiles resulting from different collision excitation processes. [ABSTRACT FROM AUTHOR]