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1
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Ortho-Positronium Annihilation in Room Temperature Ionic Liquids

100%
Hirade T.
Acta Physica Polonica A
|
2017
|
vol. 132
|
issue 5
1470-1472
EN
Very new phenomena have been found in room temperature ionic liquids, e.g. oscillation of positronium (Ps) bubble. It is almost impossible to see this kind of phenomenon in usual molecular liquids. The Ps bubble oscillations in N,N,N-trimethyl-N-propylammonium bis(trifluoro-methanesulfonyl)imide (TMPA-TFSI), N-methyl-N-propylpiperidinium bis(trifluoromethane-sulfonyl) imide (PP13-TFSI) and 1-ethyl-3-methylimidazolium thiocyanate (EMIM-SCN) were successfully observed. Even though the Ps bubble size is smaller for EMIM-SCN, the oscillation frequency of the Ps bubble at 10°C above the melting temperatures was quite similar for the other room temperature ionic liquids. Hence, the Ps bubble oscillation is, probably, caused by the repulsive force initiated by the ionic structures in room temperature ionic liquids that can remain at 10-15°C above the melting temperatures.
2
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Effect of the Initial Microstructure on Defect Evolution in Neutron Irradiated Fe-Cr-C Alloys

81%
Brodziansky T., Slugeň V., Sojak S., Petriska M., Konstantinović M.
Acta Physica Polonica A
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2017
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vol. 132
|
issue 5
1590-1592
EN
The irradiation-induced evolution of vacancy type defects in various iron-chromium model alloys and high chromium ferritic/martensitic steels have been studied using coincidence Doppler broadening spectroscopy. Specimens were neutron irradiated to 0.11 dpa at two different temperatures, 290°C and 450°C. It has been found that the microstructure (ferrite vs. ferrite/martensite), more precisely distribution of dissolved carbon within the matrix, is one of the key factor that affect response of the materials to neutron irradiation. Presence of dissolved carbon within the matrix leads to formation of stable and immobile carbon-vacancy complexes which act as traps for irradiation induced vacancies and therefore, leading to increased formation of vacancy clusters. Impact of carbon-vacancy complexes on defects evolution during neutron irradiation is relevant only for certain irradiation temperatures.
3
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Characterization of Defects in Titanium Created by Hydrogen Charging

81%
Hruška P., Čížek J., Knapp J., Melikhova O., Havela L., Mašková S., Lukáč F.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1606-1610
EN
Hydrogen interaction with vacancies in α-Ti was investigated employing positron lifetime spectroscopy combined with ab initio theoretical modeling of vacancy-hydrogen complexes. Ab initio modeling revealed that multiple hydrogen atoms up to 7 can be trapped at vacancies in the α-Ti lattice. Trapped H atoms are located close to the nearest neighbor tetrahedral sites around the centre of vacancy. Lifetimes of positrons trapped at vacancies associated with various numbers of hydrogen atoms were calculated. Positron lifetime measurement of H-loaded α-Ti samples revealed that phase transition into the hydride phase introduced dislocations. Vacancies were created by H loading as well and agglomerated into small vacancy clusters.
4
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Using a Bent Tube as an Energy Filter for a Positron Beam. Simulations on Determining the Optimum Angle of the Bend

81%
Dinescu D., Djourelov N.
Acta Physica Polonica A
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2017
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vol. 132
|
issue 5
1624-1627
EN
One way to perform lifetime measurements at a DC positron beam is to pass positrons through a pulsing device. The compressed e⁺ bunches are accelerated to a desired energy for depth profiling of the studied sample. A fraction of the e⁺ that are backscattered from the sample surface can travel back through the uniform magnetic field that is generated along the central axis of the beam transport lines and reach the accelerator. The backscattered e⁺ that reach the accelerator can be re-accelerated towards the sample and re-implant in it with a delay from the initial implanted e⁺ bunch. These e⁺ that are re-implanted into the sample with a delay cause distortions in the lifetime spectra. A setup which uses a bent tube to act as an energy filter to reduce the effect of the backscattered e⁺ is studied by simulations. The simulations are performed in order to find the optimum geometry for minimum distortions.
5
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Nanoporosity of Polymer Sorbents and Membrane Materials as Seen by PALS and Low Temperature Gas Sorption

81%
Shantarovich V., Bekeshev V., Kevdina I., Yampolskii Y., Bermeshev M., Belov N.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1548-1551
EN
The limits of application of positron annihilation lifetime spectroscopy and low temperature gas sorption for studying nanoporosity of polymer sorbents and membrane materials are discussed relying on the results previously obtained by the authors. For the two methods, limitations are determined by different factors: the dispersion of the material is essential for low temperature gas sorption, while concentration of nanopores of given size is important for positron annihilation lifetime spectroscopy. The both methods came out to be a useful addition to each other in the studies of micropores and mesopores.
6
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Positron Annihilation Lifetime Spectroscopy of ABS Objects Manufactured by Fused Deposition Modelling

81%
Dryzek M., Dryzek E.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1506-1508
EN
Positron annihilation lifetime spectroscopy was used to study acrylonitrile butadiene styrene (ABS) specimens manufactured using fused deposition modelling to explore possibilities of identifying differences in molecular structure. The set of specimens was prepared including square tiles and long rectangular tiles (100 mm and 200 mm long) with all filament roads parallel to the longer edge. All types of tiles were produced with various infill line distance parameter resulting in different overlapping of the roads in horizontal and vertical directions. The slight increase of the ortho-positronium lifetime indicating increase of the mean free volume radius was observed for the longest tiles for which influence of weld interface is expected to be most pronounced. No differences were observed for different infill line distance parameters.
7
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Free-Volume and Tensile Properties of Glass Fibre Reinforced Polyamide 6 Composites

81%
Dryzek E., Wróbel M., Juszyńska-Gałązka E.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1501-1505
EN
The tensile properties and free volume of commercially available modified polyamid 6 and polyamid 6 composites with 15 and 30 wt% of glass fibre were the subject of the studies. The tensile test allowed us to obtain the stress-strain curves and determine the tensile properties of the polyamid 6 samples. The positron lifetime measurements were performed for the samples before the test and for the samples in the vicinity of the break after they failed. The composites exhibited slightly lower values of the ortho-positronium lifetime and therefore smaller size of the local free volumes in comparison to polyamid 6 without reinforcement. The analysis of the positron lifetime spectra indicated size distribution of the free volume. The initially narrower distributions for the composite samples became broader as a result of the deformation. The deformation caused also increase of the ortho-positronium intensity in the obtained positron lifetime spectra.
8
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Free Volume of PVA/SSA Proton Exchange Membrane Studied by Positron Annihilation Lifetime Spectroscopy

81%
Gomaa M., Hugenschmidt C., Dickmann M., Abdel-Hamed M., Abdel-Hady E., Mohamed H.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1519-1522
EN
Humidity control and water management in polymer electrolyte membranes for fuel cells are still of high importance to improve the fuel cells' efficiencies. In this study, poly (vinyl alcohol) (PVA)was crosslinked using 15 wt% sulfosuccinic acid (SSA) by a solution casting method and additionally thermally crosslinked at 100°C. Positron annihilation lifetime spectroscopy was used to study the mean free volume size and the distribution at different humidity. A slight decrease in the free volume was found up to a relative humidity of 30% whereas it increases strongly for a relative humidity of more than 30%. The volume of the voids duplicates from 0.036 to 0.078 nm³ by changing the relative humidity from 30 to 80%. Thermogravimetric analyzer was used to determine the thermal stability of the membrane. From thermogravimetric analyzer data, it was found that the PVA with 15 wt% SSA membrane are chemically stable up to 200°C.
9
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Two-Component Density Functional Study of Positron-Vacancy Interaction in Metals and Semiconductors

62%
Ishibashi S.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1602-1605
EN
The positron-vacancy interaction in metals and semiconductors has been studied by the two-component density-functional-theory formalism. If a positron is not trapped at the vacancy, atoms surrounding the vacancy show inward relaxation for most cases except for nitrides, where outward relaxation is observed. The presence of positron suppresses the inward relaxation. Positron lifetimes have been calculated with and without the positron effect. The difference between two lifetime values is investigated in relation to the bulk modulus.
10
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Positronium Formation in Nanostructured Metals

62%
Čížek J., Melikhova O., Hruška P., Vlček M., Anwand W., Liedke M., Novotný M., Bulíř J.
Acta Physica Polonica A
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2017
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vol. 132
|
issue 5
1579-1584
EN
Positronium formation in Au films was studied using a magnetically guided continuous slow positron beam with variable energy. Black Au film with porous morphology was compared with conventional smooth Au film. In the smooth Au film positronium is formed on the film surface only. The black Au film exhibits porous sub-surface region containing micro-cavities interconnected with surface. Positronium is formed on inner surfaces of micro-cavities in the sub-surface region and travels through interconnected cavities towards the surface. 3-γ annihilation of ortho-positronium leaves a clear signature in two-dimensional coincidence Doppler broadening spectra. Measures of 3-γ annihilation contribution calculated from single γ-ray and coincidence Doppler broadening spectra were calculated and compared.
11
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Defect Range and Evolution in Swift Xe-Ion Irradiated Pure Silver Studied by Positron Annihilation Technique

62%
Dryzek J., Horodek P., Skuratov V.
Acta Physica Polonica A
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2017
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vol. 132
|
issue 5
1585-1589
EN
Variable energy positron beam and positron lifetime spectroscopy were used to study pure silver samples exposed to irradiation with swift Xe²⁶⁺ ions of energy 167 MeV with different dose: of 10¹³, 5×10¹³ and 10¹⁴ ions/cm². The positron lifetime spectroscopy revealed the presence of dislocations or vacancies associated with dislocations. They are distributed at the depth of about 6 μm, and this correlates with the ion implantation range, i.e. 9 μm. However, some defects are observed also to a depth of about 18 μm. At the depth less than 1 μm from the entrance surface strong dependence of positron diffusion length on the dose is observed. It indicates the presence of interstitial atoms and/or dislocation loops as a result of Xe²⁶⁺ ions implantation.
12
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Numerical Solution of a Two-Particle Model of Positronium Confined in Small Cavities

62%
Tanzi Marlotti G., Castelli F., Consolati G.
Acta Physica Polonica A
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2017
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vol. 132
|
issue 5
1575-1578
EN
The positronium atom (Ps) is widely used as a probe to characterize nanoporous and mesoporous materials. Existing theoretical models for describing Ps annihilation rates by pick-off processes generally treat Ps as a point particle confined in a potential well. Hence these models do not justify any change in the internal structure of Ps, which is experimentally accessible by means of the contact density parameter. Recently we formulated a two-particle model in which only the electron is confined in the cavity, while the positron is moving freely and feels the medium via a positive work function. We present here a numerical treatment of the problem of calculating contact densities and pick-off annihilation rates, by using a variational method. Results are in agreement with experimental data for a large class of materials, and suggest a way to connect these data with pore sizes and positron work functions.
13
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Thermal Development of Free Volumes in Nafion Membrane

62%
Melikhova O., Čížek J., Košinová L., Hruška P.
Acta Physica Polonica A
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2017
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vol. 132
|
issue 5
1538-1542
EN
In this work we employed positron lifetime spectroscopy for investigation of the thermal development of free volumes in H⁺ Nafion membrane over a broad range of temperatures from -150 to 150°C. Positron lifetime studies were combined with differential scanning calorimetry. Size distribution of free volumes was determined from ortho-positronium contribution to positron lifetime spectra. Our investigations revealed that the mean size of free volume holes strongly increases with temperature. On the other hand, the width of the size distribution and the positronium yield decreases with temperature. Transition temperatures corresponding to a change in the slope of the temperature dependence of ortho-positronium lifetime were identified. Results of positron lifetime spectroscopy agree well with the curve obtained by differential scanning calorimetry.
14
Content available remote

Chemical Information of Chitosan-Based Complex Extracted from Coincidence Doppler Broadening Spectra

62%
Cao X., Xia R., Yang J., Zeng M., Wang B., Yu R., Wei L.
Acta Physica Polonica A
|
2017
|
vol. 132
|
issue 5
1535-1537
EN
In recent years, coincidence Doppler broadening (CDB) of annihilation radiation measurement on polymeric system has been attracting special attention because of its unique elemental sensitivities in comparison to the traditional Doppler broadening measurement. In the present study, chitosan-Fe₃O₄ nanocomposite (CS-Fe₃O₄) and copper-chitosan (Cu-CS) complexes were prepared through a simple casting method from aqueous solution. The inclusion of Fe₃O₄ nanoparticles in the chitosan matrix is confirmed by X-ray diffraction. In order to obtain data about atomic composition of the annihilation site in the CS composites, CDB measurements were carried out. The normalized CDB ratio curve, which is related to the ratio between the momentum density distribution for the studied samples and pure CS, was displayed to illustrate the variation of ion cores of different elements present in the chitosan matrix. Our result confirms a contribution of active group available in chitosan molecules to the features in the high-momentum region of the CDB ratio curve. The findings show that the local chemical environment of the annihilation site in chitosan-based complexes could be estimated by such positron annihilation spectroscopic investigation.
15
Content available remote

Positronium Probing of Pores in Zirconia Nanopowders

62%
Prochazka I., Cizek J., Lukac F., Melikhova O., Hruska P., Anwand W., Liedke M., Konstantinova T., Danilenko I.
Acta Physica Polonica A
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2017
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vol. 132
|
issue 5
1564-1567
EN
In the present paper, conventional positron lifetime measurements on selected zirconia-based nanopowders are reported. The nanopowders were doped with various metal cations (Y³⁺, Eu³⁺, Gd³⁺, Lu³⁺ and Mg²⁺). Lifetime experiments were conducted in air and supplemented with mass density measurements. In a range of lifetimes, from a few ns to ≈70 ns, up to two individual lifetime components could be identified. Such observations confirmed positronium (Ps) formation with subsequent ortho-Ps pick-off annihilation as well as the occurrence of pores of different size. Pore sizes were estimated using a shape-free model of the correlation between pore size and ortho-Ps lifetime. The origins of pores are discussed on the basis of the ortho-Ps data in combination with the results of mass density measurements.
16
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A New Approach to the Presentation of the Positron Annihilation Lifetime Spectroscopy Results, n-Alkanes

62%
Zgardzińska B., Standzikowski K.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1496-1500
EN
The standard form of the positron annihilation lifetime spectroscopy results presentation are two plots of o-Ps lifetime and intensity as a function of external factor, e.g. temperature, pressure. Both o-Ps parameters change (stepwise) when in the medium phase transitions occur. For a more complete picture of the structural changes occurring in the matter we suggest to use an additional plot, in the coordinates, (τ₃, I₃). The hydrocarbons are selected to show the advantages following from the presentation of the results in the intensity-lifetime (INTI) plot.
17
Content available remote

Positronium Formation in Organic Liquids

62%
Karbowski A., Fedus K., Służewski K., Bruzdowska J., Karwasz G.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1466-1469
EN
This paper reports on the results of positron annihilation lifetime measurements of three organic liquids: benzene (C₆H₆), cyclohexane (C₆H₁₂), and methanol (CH₃OH). The lifetime spectra are acquired at different temperatures for non-degassed, degassed, and oxygen-saturated samples, at temperatures between 5°C and 25°C. The spectra are analyzed using a standard three-exponential model. The influence of oxygen on each lifetime and intensity component is discussed.
18
Content available remote

Impact of Impulse Shot Peening Parameters on Properties of Stainless Steel Surface

52%
Wiertel M., Zaleski K., Gorgol M., Skoczylas A., Zaleski R.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1611-1615
EN
Shot peening was applied to austenitic stainless steel 1.4541 (EN). The surface treatment was performed at various impact energies E, impact densities j and ball diameters D. This resulted in improved microhardness, which increases monotonically with the increase of E, j and 1/D. However, its changes with E and j achieve saturation at about 400 HV0.1. On the contrary, no saturation is observed in the investigated range for 1/D. In the un-shot peened 1.4541 (EN) steel, the lifetime component of low intensity was found with use of positron annihilation lifetime spectroscopy (PALS). It corresponds to positron annihilation from delocalized state of positrons in bulk. In the shot peened samples the bulk component is no longer observed. Instead, two types of defects can be identified: vacancy-like defects coupled with edge dislocations and vacancies or their small clusters (consisting 3÷5 vacancies). The results of PALS and hardness testing do not correspond very well, especially in the case of the samples shot peened with balls of varying diameters. The most probable reason for this are different depth profiles of both methods. It seems that the defects, which are responsible for the increase of static microhardness above 400 HV0.1 are located mostly below the surface layer penetrated by positrons.
19
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Design of an Acceleration Gap for Brightness Enhancement in a Reactor-Based Slow Positron Beamline

52%
Kuzuya Y., Oshima N., Kinomura A., Yabuuchi A.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1620-1623
EN
Design of an acceleration gap using mesh electrodes of the brightness enhancement system for the slow positron beamline of Kyoto University research reactor was studied to improve the performance of brightness enhancement. The transmittance and the increase in the angular divergence of the beam resulting from acceleration with the mesh electrode were estimated by trajectory simulations. The effect of the increase in the beam emittance on the beam radius at the focus point was estimated based on the analytical solution of the beam envelope equation. Using the obtained beam transmittance and beam radius, the beam brightness after remoderation was evaluated. Then, the influence of the mesh electrode configuration on the brightness was investigated.
20
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Aerogel IC3120 Under High Pressure Exerted Mechanically and by Nitrogen

52%
Gorgol M., Zgardzińska B.
Acta Physica Polonica A
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2017
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vol. 132
|
issue 5
1531-1534
EN
Highly porous IC3120 silica aerogel was subjected to the high pressure up to 450 MPa while the positron annihilation lifetime spectra were collected. The pressure was delivered to the investigated samples in two ways: by pistons and by gas (nitrogen) penetrating the aerogel. The evolution of all PALS parameters was discussed. With the increase of the pressure, shortening of ortho-positronium lifetimes (different, depending on the pressure method introduced) was observed. Similarity between the dependence of the longest-lived o-Ps component lifetime on the pressure, for the sample affected with nitrogen molecules and pure nitrogen was observed. It suggests, that the nitrogen fills the largest free volumes of the aerogel. The pressure exerted mechanically causes much smaller decrease of free volume available for positronium. The comparison of PALS results with the electron microscopy images, obtained after removing the pressure, confirmed that more intense and lasting changes were caused by affecting the aerogel with the pistons.
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