Search results

1

Magnetron Sputtered SnO_{x} Films on Tin Probed by Slow Positron Implantation Spectroscopy

100%

Nancheva N., Docheva P., Anwand W., Brauer G., Coleman P.

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vol. 95

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issue 4

623-626

EN

SnO_{x} films grown on tin substrates via d.c. magnetron sputtering at different bias were studied by slow positron implantation spectroscopy. The change of substrate bias from -40 V to -140 V and its influence on the films is shown and discussed.

2

Positron Implantation Profile in Kapton

100%

Dryzek J., Dryzek E.

Acta Physica Polonica A

|

2006

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vol. 110

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issue 5

577-582

EN

The discussion presented in the paper focuses on processes accompanying positron implantation in condensed matter. They finally constitute the positron implantation profile which generally does not exhibit the exponential behavior as it is concluded from the Monte Carlo simulation made using the EGSnrc 4.0 code. The simulation was performed for the kapton and two commonly used positron sources ^{22}Na and ^{68}Ge/g^{68}Ga. New formula for the implantation profile was proposed.

3

Partial Probabilities of X-Ray Bremsstrahlung Transitions

63%

Nietubyć R., Sobczak E., S̆imůnek A., Vackár̆ J., S̆ipr O.

Acta Physica Polonica A

|

1997

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vol. 91

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issue 5

841-846

EN

High-energy electrons bombarding a solid produce X-ray bremsstrahlung radiation, which is one of few elementary processes occurring during electron-solid interactions. Photon emission results from electron transition to an unoccupied electron state above the Fermi level. In this work matrix elements of X-ray bremsstrahlung transitions were calculated for solids containing elements from N (Z=7) to Pd (Z=46) and photon energies 1487 eV and 5415 eV. It was found that in the case of light elements the X-ray bremsstrahlung transitions to s-type final states dominate over all other symmetries. It was also shown that X-ray bremsstrahlung transition probabilities increase with decreasing photon energy and increasing atomic number Z. Dependence of X-ray bremsstrahlung transition probabilities on the electron final state energy is also presented in this work.

4

A Simplified Method for the Estimation of Hole Free Volume Fraction from the Specific Volume

63%

Dlubek G., Pionteck J.

Acta Physica Polonica A

|

2008

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vol. 113

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issue 5

1331-1338

EN

A brief introduction in the equation of state of the Simha-Somcynsky hole theory is presented. This theory allows to calculate the volume fraction h of free volume holes from pressure-volume-temperature experiments. These holes are detected by ortho-positronium and from the value of h and the mean ortho-positronium hole size the hole density may be calculated. We discuss a simplified method to estimate h which makes use of the relation V* = 1.52V_W between the scaling volume V* of the Simha-Somcynsky hole theory equation of state and the van der Waals volume V_W. Moreover, we present a new simplified method for the estimation of h which starts with the Schottky (Arrhenius) equation for the concentration of thermal vacancies and makes use of a linear relation between the scaling temperature T* and the hole formation enthalpy H_h, H_h(kJ/mol)=6.54×10^{-4}T*(K).

5

Chemical Effects on the K_{β}/K_{α} Intensity Ratios in First-Row Transition Element Compounds

63%

Küçükönder A., Büyükkasap E., Yilmaz R., Şahin Y.

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vol. 95

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issue 2

243-250

EN

Chemical Effects on the K_{β}/K_{α} X-ray Intensity Ratios for Some First-row Transition Element Compounds Were Studied Experimentally and Calculated. the Vacancies in the K Shell Were Created by 59.5 keV γ rays from an ^{241}Am Radioactive Source and Characteristic X-ray Radiation from Sample Was Measured by Using Si(li) and Ge(li) Detectors. the Calculations Were Carried Out Using Brunner's Model. the Calculated Relative K_{β}/K_{α} X-ray Intensity Ratios Are in Good Agreement with the Present and the Previously Published Experimental Data.

6

The Temperature and Pressure Dependence of the Free Volume in Fluoroelastomers from PALS and PVT Experiments

63%

Dlubek G., Sen Gupta A., Wawryszczuk J., Kilburn D., Pionteck J., Krause-Rehberg R., Goworek T., Alam M., Kaspar H., Lochhaas K.

Acta Physica Polonica A

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2005

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vol. 107

|

issue 4

685-689

EN

Positron lifetime and pressure-volume-temperature experiments were performed as function of T (100-485 K) and P (10^{-5} Pa-500 MPa) on a fluoroelastomer. From positron annihilation lifetime spectroscopy, analyzed with LT9.0 assuming a dispersion in the e^+ (τ_2) and o-Ps (τ_3) lifetime, the mean, 〈v_h〉, and the width (standard deviation), σ_h, of the hole size distribution were calculated. The pressure-volume-temperature data were analyzed using the Simha-Somcynsky hole-lattice theory to estimate the specific hole free volume V_f. From a comparison of V_f with 〈v_h〉 the specific hole number, N'_h, is estimated. The data from thermal expansion and pressure experiments show complete agreement when taking into account the compressibility of the occupied volume.

7

Relations Between Hole Volume and Macroscopic Volume in Various Polymers

51%

Dlubek G., Alam M., Saarinen K., Stejny J., Fretwell H.

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vol. 95

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issue 4

521-526

EN

Different definitions of the free volumes are discussed and related to the total specific volume and to the local free (hole) volume. Positron lifetime measurements are reported for polyethylene, polytetrafluoroethylene, and CR39-copolymers. Two long-lived components appear in polyethylene and polytetrafluoroethylene, which were attributed to o-Ps annihilations in crystalline regions and in holes of the amorphous phase. From a relation between the coefficients of the thermal expansion of macroscopic and hole volume, the fractional hole volume h and from this the number of holes, N, is estimated. Values of T_{g}=195 K, h_{g}=4.5% (polyethylene) and 5.7% (polytetrafluoroethylene) and N_{g}=0.73 nm^{-3} (polyethylene) and 0.36 nm^{-3} (polytetrafluoroethylene) were obtained. In semicrystalline polymers these values agree with estimates obtained from the densities of the crystalline and amorphous phases. The effect of cross-linking on the free-volume properties of CR39-copolymer networks was studied. The comparison of the hole volume with the specific volume allowed us to estimate the number density of holes to ≈1 nm^{-3}.

8

Electrical Resistivity and Positron Lifetime Studies of Precipitation Effects in Al-Cu Alloy

51%

Αda P., Cieslar M., Vostrý P., Bečvář F., Νovotný I., Procházka I.

Acta Physica Polonica A

|

1995

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vol. 88

|

issue 1

111-117

EN

Decomposition of the supersaturated solid solution of 2 at.% Cu in Al was investigated by means of electrical resistivity and high-resolution positron lifetime measurements. The phase composition of this alloy was determined by transmission electron microscopy. Electrical resistivity measurements were performed by a classical four-point method. Positron lifetime spectra were measured by means of a spectrometer consisting of two BaF_{2} detectors and a standard fast-slow coincidence system. The specimens were first exposed to the solution heat treatment at 783 K for 19 hours with a subsequent quenching. Then the specimens were isochronally annealed in the temperature range 293 ÷ 573 K. Annealing responses of electrical resistivity and positron annihilation were studied. Resistivity measurements as well as transmission electron microscopy observations confirmed the well-known decomposition sequence of the Al-Cu alloy. The decomposition of the alloy was manifested by the decrease in the intensity of positron lifetime component τ_{2} = (207 ±2 ) ps correlated with simultaneous appearance and increase in the intensity of τ_{3} = (180 ± 5) ps component. Component τ_{2} originates from positron annihilation in vacancies trapped at the Guinier-Preston zones while τ_{3} comes from annihilation of the positrons localized in the misfit dislocations at coherent precipitates of the Al_{2}Cu phase. The shortest observed component τ_{1} apparently belongs to annihilation of untrapped positrons.

9

Structure of Free Radical inγ-Irradiated 21-Hydroxyprogesterone (Deoxycorticosterone) Single Crystals. ESR/ENDOR and DFT Studies

51%

Szyczewski A., Pietrzak J., Möbius K.

Acta Physica Polonica A

|

2005

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vol. 108

|

issue 1

119-126

EN

Single crystals of 21-hydroxyprogesterone have been γ-irradiated at 295 K and studied using X-band ESR and ENDOR. The structure of the one type radical has been determined on the basis of an analysis of the angular variation of the spectra. This radical is formed by abstraction of the hydrogen atom from the C(6) carbon, while the unpaired electron is delocalised onto the system O(3), C(3), C(4), C(5), C(6). Hyperfine splitting constants and unpaired electron density distribution have been calculated for the proposed radical structure by using the Gaussian98 set of programs. The results are in very good agreement with the experimental data. The effect of the hydrogen bond and biological activity on the anisotropy of α-hyperfine splitting tensor have also been discussed.

10

Environmental Gamma Dose Evaluation During Explosive Materials Analysis by PGNAA Technique Using MCNPX Code

51%

Nasrabadi M., Omidi S.

Acta Physica Polonica A

|

2015

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vol. 127

|

issue 4

961-964

EN

Increased use of radiation in medicine, industry, and laboratories, requires safe conditions to be provided for its optimal use. One of the cases in which people are exposed to radiation, is during the detection of explosive materials by PGNAA method. Therefore, external dosimetry is necessary for workplaces where the method is used. In this study, Monte Carlo simulation program, MCNPX has been used to simulate gamma dose in the environment during the detection of explosive materials by PGNAA method. The simulated results were validated practically. The results indicate a good agreement between the simulated and measured data. The study demonstrated that MCNPX code can be used effectively for simulating gamma dose in various environments.

11

X-Ray Magnetic Scattering

51%

Cooper M.

Acta Physica Polonica A

|

1992

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vol. 82

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issue 1

137-146

EN

Magnetic X-ray diffraction with synchrotron radiation is now an established technique for studies of antiferromagnets. The problems associated with the small magnetic scattering cross-section being alleviated by the dramatic enhancements found near absorption edges through resonant exchange scattering. The technique is particularly useful for those materials that require high wavevector resolution to reveal the structural phase transitions that accompany the magnetic ordering process or those that are difficult to investigate with neutrons, (e.g. samarium, for which recent results are presented). In the actinides the work is also motivated by the objective of performing an empirical separation of the spin and orbital components of magnetisation. Diffraction studies of ferromagnets require circular polarised radiation and suffer from the superposition of the small magnetic signal and the charge scattering; to date Laue methods have proved more successful than monochromatic beam studies. Ferro- and ferrimagnets can also be studied by Compton (inelastic) scattering but the cross-section is less well established: considerable effort has been directed to determining whether orbital magnetisation can be measured in these experiments and results on HoFe2 now indicate this is not so. Magnetic Compton profiles provide information about the momentum distribution of electrons with unpaired spins, and this, together with magnetisation data can provide the basis for the separation of spin and orbital magnetisation.

12

Ultramarine, Lazurite and Sodalite Studied by Positron Annihilation and EPR Methods

51%

Baranowski A., Dębowska M., Jerie K., Jezierski A., Sachanbiński M.

Acta Physica Polonica A

|

1995

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vol. 88

|

issue 1

29-41

EN

Studies of positron annihilation accompanied by EPR technique were undertaken for sodalite and lazurite and their synthetic counterparts (synthetic sodalite and ultramarines). Results of measurements performed by two techniques of positron annihilation spectroscopy (angular correlation of annihilation radiation, ACAR, and positron annihilation lifetime) revealed the undoubted influence of free radicals on positron annihilation mechanism but both inhibition of positronium formation by them and the effect of filling cages ought to be taken into account. The distinct differences between ACAR curves for sodalites, lazurites and ultramarines probably reflect the presence of different radicals in their cages and chemical heterogeneity as well as the disorder in Al, Si-site ordering in case of ultramarines. Comparison of the results of ACAR measurements with the ones of the EPR studies indicates that there is correspondence between them. Similarly to three families of the ACAR curves, different likes of EPR lines were obtained for three groups of samples; sodalites, lazurites and ultramarines. It is possible that the annihilation of positrons takes place mainly with unpaired electrons recorded by the EPR technique.

13

Peculiarities of High Power Infrared Detection on Narrow-Gap Semiconductor p-n Junctions

51%

Gradauskas J., Širmulis E., Ašmontas S., Sužiedėlis A., Dashevsky Z., Kasiyan V.

Acta Physica Polonica A

|

2011

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vol. 119

|

issue 2

237-240

EN

We report on experimental results of photosignal investigation in HgCdTe, InSb and PbTe semiconductor p-n junctions under the action of an intense pulsed CO_2 laser. The influence of laser power, external bias voltage as well as the diode temperature on the photosignal formation has been studied. We show that under certain conditions both classical photovoltaic and hot carrier phenomena may act simultaneously within a junction thus strongly impacting on responsivity and speed of operation of the device. The drawn conclusions may be of great importance for the development of high power optoelectronic devices.

14

Charge Transfer Dynamics in Atom-Metal Surface Collisions

51%

Wiertel M., Taranko R., Taranko E.

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vol. 96

|

issue 6

769-783

EN

We study the charge exchange in atom-metal collisions in the framework of the generalized time-dependent Anderson-Newns model. The electron correlations and correlated hopping are treated within the mean-field approximation. The resulting one-particle model with an effective spin-dependent atom-surface coupling is used to study the charge transfer in scattering of Na and Li atoms on metal surfaces. It is shown that the effective occupation dependent atom-surface coupling influences mainly the expectation values for producing positive, neutral, and negative particles for small work functions and high atom velocities. It is also shown that the temperature dependence of these expectation values is more visible, especially for magnetic solutions.

15

Electron Beam Induced Modification of Polymer-Like Carbon Coatings

51%

Plaipaitė-Nalivaiko R., Adlienė D., Adlys G.

Acta Physica Polonica A

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2013

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vol. 123

|

issue 5

871-873

EN

Carbon coatings can possess diamond-like, polymer-like, graphite-like or other properties depending on deposition methods and technological parameters. Structural changes in the polymer-like carbon coatings irradiated by high energy electrons are discussed in the present paper. The polymer-like carbon coatings have been synthesized from C_2H_2 gas in the radio frequency dual-plasma reactor using various deposition parameters. Plasma enhancement chemical vapor deposition deposited experimental polymer-like carbon samples were irradiated with high energy electrons in the medical linear accelerator. The investigations of carbon coatings have been carried out using the Fourier-transform infrared, Raman and UV-VIS spectroscopies. Modification of the polymer-like carbon coatings is discussed in relation with radiation induced formation of free radicals and unsaturated bonds along with possible cross-linking processes.

16

Control of Radiation Sensitivity of the Oxygen-Containing Fluorite Crystals

51%

Kachan S., Salapak V., Nahurskiy O., Pirko I.

Acta Physica Polonica A

|

2018

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vol. 133

|

issue 4

824-828

EN

The parameters of radiation sensitivity of the oxygen-doped fluorite crystals were calculated in a one-dimensional model. The limit concentrations of the color centers as a function of the concentration of the oxygen impurity in the fluorite crystal were defined. Fluorite crystals with anti-Frenkel defects in the anion sublattice of the crystal have a specific property: the discolored after irradiation crystal being irradiated repeatedly with ionizing radiation retains the "memory" of the preceding irradiation. Using an ion chain model this paper studies under what conditions the "radiation memory" effect can arise in the MeF₂-O²¯ crystals as well as the extent of its contribution into the overall radiation sensitivity of the crystal.

17

Radiation Defects in CaF_2-CaO Crystals

51%

Kachan S., Obukhova E., Shtanko V., Chinkov E.

|

EN

The spectral and kinetic parameters of electron-pulse-initiated transient absorption of oxygen-doped CaF_{2} crystals were studied using pulsed spectrometry with a nanosecond time resolution. It is shown that the formation of a M_{A}^{+} color centers in CaF_{2}-0.01M%CaO crystals occurs by thermally activated diffusion of the vacancies. Activation energy of M_{A}^{+} color centers formation process of 0.4 eV is established.

18

Temperature Dependent Variations of Properties of Polymer-Like Carbon Coatings Treated with High Energy Electrons

51%

Plaipaitė-Nalivaiko R., Vigricaitė L., Adlienė D., Rutkūnienė Ž.

Acta Physica Polonica A

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2015

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vol. 128

|

issue 5

915-917

EN

Polymer-like carbon coatings can be used for the protection of micro-electromechanical devices functioning in chemically or radiation harsh environment due to their beneficial properties. Properties of carbon coatings depend on the method of synthesis, initial gas mixture, admixture of additives, temperature and other technological parameters. Modification of carbon structures is possible applying high energy electrons. Coating mechanical properties become almost stable after their pretreatment with some doses of high energy electrons. Polymer-like carbon coatings were synthesized from acetylene gas plasma on n-type silicon substrates in the RF plasmotron system at temperatures in the range 293-673 K using plasma enhanced chemical vapor deposition method. Series of samples were prepared and irradiated with high energy (6 MeV) electrons in a medical linear accelerator. The ellipsometric method was used for estimation of some optical parameters and thickness of synthesized coatings. Structural changes of polymer-like carbon coatings were evaluated using the Raman spectroscopy and surface morphology was assessed by atomic force microscopy. Electron beam induced structural changes in the coatings were analyzed using the obtained results. The relations between the synthesis temperature and samples structure and surface morphology are discussed.

19

Influence of Irradiation by High-Energy Protons on GaN Detectors

45%

Kažukauskas V., Kalendra V., Vaitkus J., Jasiulionis R.

Acta Physica Polonica A

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2008

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vol. 113

|

issue 3

1013-1016

EN

We had investigated effects of the irradiation by 24 GeV protons with doses ranging from 1×10^{14} up to 1×10^{16} p/cm^2 on the properties of GaN ionising radiation detectors. In theγ-spectra of the samples radiation of ^7Be, ^{22}Na, and other long-lived radionuclides with A <70 was identified. Their activities were proportional to the irradiation dozes. Device contact properties were analysed by current-voltage I-V dependences. Created defects were revealed by the thermally stimulated defect spectroscopy. In the less irradiated samples the following values of the effective thermal activation energies were found: 0.12-0.16 eV, 0.18-0.22 eV, 0.35-0.42 eV, and 0.84-0.94 eV. Meanwhile, in the detectors irradiated with the highest doses only current growth with the activation energy of about 0.8-1.0 eV could be identified. Effects of percolation transport in disordered media were proved in the irradiated material.

20

Investigation of Carrier Transport in GaN Single Crystals and Radiation Detectors by Thermally Stimulated Methods

45%

Kažukauskas V., Kalendra V., Vaitkus J.

Acta Physica Polonica A

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2005

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vol. 107

|

issue 2

340-345

EN

We investigated single crystals of GaN and thin film GaN radiation detectors by thermally stimulated currents and thermally stimulated depolarization methods in order to characterize carrier transport properties as influenced by material defect structure. In thick GaN no expressed structure of the thermally stimulated current spectra was observed in the temperature range from 100 K up to 350 K, which could be characteristic of the thermal carrier generation from trap levels. The experimental facts imply that the thermally stimulated current spectra might be caused not by carrier generation, but it could be due to thermal mobility changes. Therefore we had applied the numerical analysis by taking into account carrier scattering by ionized impurities and phonons. It was found that mobility limited by ionized impurities varies as T^{2.8} and lattice scattering causes the dependence T^{-3.5}. The highest mobility values were up to 1550 cm^2/(V s) at 148-153 K. Such high values indicate relatively good quality of the single GaN thick crystals. In high resistivity GaN detectors irradiated by high doses of high-energy neutrons and X-rays current instabilities were observed which could be caused by the change of carrier drift paths in a highly disordered matter. A model of carrier percolation transport is presented.

Refine search results

Magnetron Sputtered SnO_{x} Films on Tin Probed by Slow Positron Implantation Spectroscopy

Positron Implantation Profile in Kapton

Partial Probabilities of X-Ray Bremsstrahlung Transitions

A Simplified Method for the Estimation of Hole Free Volume Fraction from the Specific Volume

Chemical Effects on the K_{β}/K_{α} Intensity Ratios in First-Row Transition Element Compounds

The Temperature and Pressure Dependence of the Free Volume in Fluoroelastomers from PALS and PVT Experiments

Relations Between Hole Volume and Macroscopic Volume in Various Polymers

Electrical Resistivity and Positron Lifetime Studies of Precipitation Effects in Al-Cu Alloy

Structure of Free Radical inγ-Irradiated 21-Hydroxyprogesterone (Deoxycorticosterone) Single Crystals. ESR/ENDOR and DFT Studies

Environmental Gamma Dose Evaluation During Explosive Materials Analysis by PGNAA Technique Using MCNPX Code

X-Ray Magnetic Scattering

Ultramarine, Lazurite and Sodalite Studied by Positron Annihilation and EPR Methods

Peculiarities of High Power Infrared Detection on Narrow-Gap Semiconductor p-n Junctions

Charge Transfer Dynamics in Atom-Metal Surface Collisions

Electron Beam Induced Modification of Polymer-Like Carbon Coatings

Control of Radiation Sensitivity of the Oxygen-Containing Fluorite Crystals

Radiation Defects in CaF_2-CaO Crystals

Temperature Dependent Variations of Properties of Polymer-Like Carbon Coatings Treated with High Energy Electrons

Influence of Irradiation by High-Energy Protons on GaN Detectors

Investigation of Carrier Transport in GaN Single Crystals and Radiation Detectors by Thermally Stimulated Methods