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Strona główna » Instytut » Pracownicy » Radosław Zaleski

dr hab. Radosław Zaleski


Zakład Metod Jądrowych


prof. UMCS


pokój: 255
telefon: (081) 537-61-45
e-mail: radek@zaleski.umcs.pl

Specjalność naukowa:


Publikacje: Ukryj abstrakty

  1. R. Zaleski,W. Stefaniak,M. Maciejewska,J. Goworek, Porosity evolution of VP-DVB/MCM-41 nanocomposite, Journal of Colloid Interface Science, 343(), 2010, 134-140

  2. R. Zaleski,J. Wawryszczuk,K. Sobczak, Positron annihilation lifetime spectroscopy study of thermal processing and rehydration of dry leek (Allium porrum L.), Nukleonika, 55(), 2010, 73-78

  3. J. Goworek,R. Zaleski,W. Buda,A. Kierys, Free volumes evolution during desorption of n-heptane from silica with regular pore geometry. Positron annihilation study, Applied Surface Science, 256(), 2010, 5316-5322

  4. Z. Surowiec,M. Wiertel,R. Zaleski,M. Budzyński, Positron annihilation study of iron oxide nanoparticles in mesoporous silicate MCM-41 template, Nukleonika, 55(), 2010, 91-96

  5. R. Zaleski, W. Stefaniak, M. Maciejewska, J. Goworek, Porosity evolution of VP-DVB/MCM-41 nanocomposite, Journal of Colloid and Interfarce Science, (), 2009, doi:10.1016/j.jcis.2009.11.019

  6. R. Zaleski, W. Stefaniak, M. Maciejewska, J. Goworek, Porosity of polymer materials by various techniques, Journal Porous Mater, 16(), 2009, 691-698

  7. R. Zaleski, J. Goworek, n-Nonadecane embedded in mesopores, Material Science Forum, 607(), 2009, 180-182

  8. R. Zaleski, J. Goworek, M. Maciejewska, Positronium lifetime in porous VP-DVB copolymer, Physica status solidi c, 6(), 2009, 2445-2447

  9. J. Kansy, R. Zaleski, Positronium thermalization process in nanoporous materials and its influence on the shape of PALS spectrum, Material Science Forum, 607(), 2009, 39-41

  10. T. Goworek, M. Pietrow, R. Zaleski, B. Zgardzińska, Positronium in high temperature phases of long-chain even alkanes, Chemical Physics, 355(), 2009, 123-129

  11. Zaleski, R. Wawryszczuk, J., Positron porosimetry studies of template removal from as-synthesized MCM-41 silica, Acta Physica Polonica A, 113(), 2008, 1543-1550

  12. Zaleski, R. Zgardzińska, B. Pietrow, M. Goworek, T., Positron irradiation effects in simple organic solids, Radiation Physics and Chemistry, 77(), 2008, 1306-1310

  13. Zgardzińska, B. Zaleski, R. Wawryszczuk, J. Pietrow, M. Goworek, T., Intermolecular free volumes and intramolecular defects in alkanes,Czech Republic, Praha, Abstract of International workshop, Positron studies in defects, (), 2008, 50

  14. Goworek, T. Wawryszczuk, J. Zaleski, R. Zgardzinska, B., Positronium in solid phases of long-chain paraffins, Radiation Physics and Chemistry, 76(2), 2007, 185-188

    The study of positronium intensity rise in long-chain alkanes shows two kinds of electron traps: the first, which are discharged at low temperature (200 K); the other, which remain populated up to the transition point to the rotator phase; e.g. in C30H62 they are still observed at 328 K. In the rigid phase of even-numbered alkanes o-Ps lifetime is shorter than that of odd-numbered ones, due to the difference in the width of gap between the molecular lamellae. (c) 2006 Elsevier Ltd. All rights reserved.

  15. Zaleski, R. Wawryszczuk, J. Goworek, T., Pick-off models in the studies of mesoporous silica MCM-41. Comparison of various methods of the PAL spectra analysis, Radiation Physics and Chemistry, 76(2), 2007, 243-247

    The results of models, extending the Tao-Eldrup model to free volume radii R > 1 nm, are discussed. The influence of free volume size and geometry on ortho-positronium lifetime was examined. Theoretical curves were compared to available experimental data. Then the models were used to obtain information about free volume sizes in MCM-41 porous silica. Numerical analysis of MCM-41 lifetime spectra is difficult due to their considerable complexity. In order to verify the results, various methods of PAL spectra analysis, e.g., deconvolution, fitting, etc., were involved. (c) 2006 Elsevier Ltd. All rights reserved.

  16. Zgardzińska, B. Goworek, T. Zaleski, R. Wawryszczuk, J., Positron annihilation and phase transitions in argon intercalated n-nonadecane, Chemical Physics, 335(), 2007, 1-6

  17. Pietrow, M. Zaleski, R. Goworek, T., Positronium in 1-tridecene, Chemical Physics, 342(), 2007, 85-89

  18. Zaleski, R. Goworek, J. Kierys, A., Temperature dependence of positronium lifetime in cylindrical pores, Physica Status Solidi B, 4(), 2007, 3814-3818

  19. Jasińska, B. Zaleski, R. Śniegocka, M. Reisfeld, R. Zigansky, E., Testing ETE model, temperature dependences of PALS data, Physica Status Solidi B, 4(), 2007, 3985-3988

  20. Sniegocka, M. Jasinska, B. Goworek, T. Zaleski, R., Temperature dependence of o-Ps lifetime in some porous media. Deviations from ETE model, Chemical Physics Letters, 430(4-6), 2006, 351-354

    Temperature dependence of ortho-positronium lifetime in some porous materials was investigated. Above the room temperature the extended Tao-Eldrup model works rather well, however at low temperatures one observes in all samples the lifetimes evidently longer than expected. (c) 2006 Elsevier B.V. All rights reserved.

  21. Zaleski, R., Measurement and analysis of the positron annihilation lifetime spectra for mesoporous silica, Acta Physica Polonica A, 110(5), 2006, 729-738

    Positron annihilation lifetime spectroscopy as a technique of porous materials investigation is still under development. Both measurement conditions and lifetime spectra analysis methods have to be adapted to the requirements of positron porosimetry. If complex positron annihilation lifetime spectra of porous materials are processed, numerical methods of lifetime spectra analysis have to be used with a particular care. Among various methods of positron annihilation lifetime spectra analysis available, the most popular ones were tested implemented in programs MELT and LT. It was found, from the simulated spectra study, that a large number of counts in a spectrum is needed to obtain reliable results of analysis. Even then only an approximate solution is available. Determination of the approximation nature helps in a further interpretation of the results and in positron annihilation lifetime spectrometer setting adequate to the problem. For this purpose, a few complex spectra obtained from positron beam facility were tested. The results show a negligible influence of resolution function on long lifetime components, while the precise estimation of the background level is crucial. Also some distortions caused by imperfection of numerical analysis methods are pointed out.

  22. Zaleski, R. Zaleski, K., Positron annihilation in steel burnished by vibratory shot peening, Acta Physica Polonica A, 110(5), 2006, 739-746

    A series of C45 steel samples was burnished by shot peening with varying time of treatment. The samples were investigated by nondestructive positron annihilation techniques: angular correlations of two-quantum annihilation radiation and positron annihilation lifetime spectroscopy. To determine residual stresses present under burnished surface the same samples were studied by destructive Davidenkov method. Change of absolute value of the weighted average of residual stresses over positron range in the series of the samples is in good agreement with change of S/W ratio obtained by angular correlations of two-quantum annihilation radiation. Both parameters increase during first 10 minutes of shot peening and then stabilize. Positron annihilation lifetime spectra allowed to identify two types of structural defects: smaller ones like vacancies or dislocations and bigger - probably clusters of vacancies. Increase in shot peening time causes reduction of positron trapping rate and lifetime rise in bigger defects.

  23. Goworek, T. Wawryszczuk, J. Zaleski, R., Pressure effects in ortho-positronium annihilation, Acta Physica Polonica A, 107(4), 2005, 608-614

    A short review of experiments concerning the influence of high pressure on positron annihilation in molecular solids is given. To this kind of experiments belong e.g. pressure inhibition of positronium formation, pressure induced phase transitions, and free volume swelling in the media, intercalated by high pressure gas.

  24. Zaleski, R. Wawryszczuk, J. Goworek, T., Positronium formation in solid long-chain alkanes, Acta Physica Polonica A, 107(4), 2005, 635-641

    This paper represents a fragment of systematic studies on positron annihilation in solid saturated hydrocarbons (alkanes, paraffins) from C17H36 to C30H62. The Tao-Eldrup model and its extensions allow to identify the places in the crystalline structure where positronium is trapped, and estimate respective trap sizes. In the rigid phase I positronium locates mainly in two-dimensional empty spaces between the lamellae of crystal structure. Additional free volumes exist in high temperature phases due to appearance of n-alkane conformers representing a non-planar molecule distortion. The rise of ortho-positronium intensity with the sample irradiation dose, which was seen earlier in polymers, is observed also in n-alkanes. One can find similarities between the ortho-positronium annihilation in crystalline alkanes and polymers, like exponential character of that rise, and the a trap bleaching by illumination. It confirms the same origin of the intensity growth, i.e. the accumulation of trapped electrons. Two kinds of electron traps were found. The time constant of electron accumulation in the traps depends on the carbon chain length and varies with temperature in different way for even- and odd-numbered alkanes.

  25. Goworek, T. Wawryszczuk, J. Zaleski, R., Negative compressibility of free volumes in argon intercalated n-nonadecane, Chemical Physics Letters, 402(4-6), 2005, 367-369

    Positron annihilation lifetime spectroscopy was applied to study modification of sub-nanometer voids in one of n-alkanes subjected to high pressure. Without a contact with gaseous atmosphere the sizes of voids behaved as expected - decreased with the rise of pressure. When the pressure was applied with argon penetrating the samples - the voids expanded. After the phase transition the structure damage allowed positronium, trapped in voids, to escape out of a damaged sample. (C) 2004 Elsevier B.V. All rights reserved.

  26. Jasinska, B. Wawryszczuk, J. Zaleski, R., Three-quantum annihilation in porous vycor glass, Acta Physica Polonica A, 107(5), 2005, 821-825

    Three methods of determination of 3 gamma o-Ps decay intensity are compared. The estimate of 3 gamma fraction obtained from classical lifetime measurements can be distorted due to a higher absorption of the gamma quanta from the continuous spectrum of three-quantum decay, compared to two-quantum one.

  27. Sniegocka, M. Jasinska, B. Wawryszczuk, J. Zaleski, R. Derylo-Marczewska, A. Skrzypek, I., Testing the extended Tao-Eldrup model. Silica gels produced with polymer template, Acta Physica Polonica A, 107(5), 2005, 868-873

    The temperature dependence of o-Ps lifetime in the pores calculated from extended Tao-Eldrup model was compared to the experimental data, collected for a set of silica gels synthesized using the polymer template technique. For the sample with average pore radii 2.0 nm rather good agreement between the model and experiment was found. For the sample with narrow pores (near 1.0 nm) the lifetime spectrum was complex. Except the range of highest temperatures the lifetimes are far from model calculations.

  28. Goworek, J. Borowka, A. Zaleski, R. Kusak, R., Template transformations in preparation of MCM-41 silica, Journal of Thermal Analysis and Calorimetry, 79(3), 2005, 555-560

    Template transformation in MCM-41 material during thermal treatment under different conditions was investigated on the basis of thermogravimetry (TG-DTA), X-ray diffraction (XRD) and positron annihilation lifetime spectroscopy (PALS). Micelle templated silica was prepared using C18 trimethylammonium bromide. The pore structure of MCM-41 samples obtained after removal of the surfactant in air, argon flow and vacuum was analyzed on the basis of the adsorption isotherms of nitrogen at 77 K and XRD experiments. The TG-DTA experiments confirm the mechanism of the template removal known from literature. However, the sequence of the processes during thermal treatment of as-synthesized sample and temperature of transformations depended strongly on the presence of oxygen and the heating rate. The main template degradation took place below 573 K and was independent of the kind of atmosphere above the sample. Residual carbonaceous species are removed from pores and the external surface of MCM-41 silica upon heating to 823 K by combustion or evaporation. The latter process as well as translocation of liquid-like products of template degradation from the pore interior to external surface was confirmed by PALS experiment in vacuum.

  29. Zgardzinska, B. Zaleski, R. Wawryszczuk, J. Goworek, T., Positronium in solid phases of n-pentacosane, Physics Letters A, 333(3-4), 2004, 341-346

    Positron annihilation lifetime spectra in solid n-pentacosane were measured as a function of the temperature and positron irradiation time. Phase IV was found to be well visible in the cooling runs due to its easy supercooling; a small increase of ortho-Ps lifetime in phase IV compared to low-temperature phase indicates that predominant intramolecular defects are end- gauche ones. The effect of excess electron accumulation, typical mainly of polymers, was also observed; two kinds of electron traps were found. The main trap component had activation enthalpy 0.6 eV and disappeared at about 250 K; an additional fast accumulating component existed up to the temperatures near the transition to the rotator phase. (C) 2004 Elsevier B.V. All rights reserved.

  30. Goworek, T. Zaleski, R. Wawryszczuk, J., Observation of intramolecular defects in n-alkanes C25H52- C29H60 by the positron annihilation method, Chemical Physics Letters, 394(1-3), 2004, 90-92

    The lifetime of ortho-positronium (o-Ps) in solid phases of long-chain n-alkanes was measured. In even-numbered alkanes, only one phase transition is observed; a very long lifetime is related to large free volumes near kink-shaped conformers. In odd-numbered alkanes (n less than or equal to 25), another solid phase (phase IV) is characterized by slightly increased o-Ps lifetime, which means the domination of end-gauche and double-gauche intramolecular defects. In C29H60 the structure of defects changes continuously in the whole range of phase IV. (C) 2004 Elsevier B.V. All rights reserved.

  31. Goworek, T. Wawryszczuk, J. Zaleski, R., Positronium inhibition in naphthalene at high pressures, Chemical Physics Letters, 387(4-6), 2004, 433-435

    The lifetime Of ortho-positronium in solid naphthalene shortens with the rise of pressure as a result of diminishing the free spaces in which it is trapped. At the pressure approximate to100 MPa the size of these spaces is too small to accommodate the Ps atom (no energy level in the well), and the intensity of ortho-Ps component. initially weakly dependent on pressure, abruptly drops to zero. The narrow range in which ortho-Ps disappears indicates uniformity of Ps-accommodating voids. The nonmonotonous dependence of free positron lifetime is discussed in the framework of the blob model. (C) 2004 Elsevier B.V. All rights reserved.

  32. Djourelov, N. Goworek, T. Kondo, K. Suzuki, T. Zaleski, R., Enhancement of positronium formation by trapped electrons in solid n-nonadecane. Light bleaching effect, Physics Letters A, 323(3-4), 2004, 165-168

    The increase of positronium, formation probability with the time of exposure to positron radiation, observed until now mainly in polymers, is shown for the case of polycrystalline n- nonadecane. Sample illumination by visible light restores the initial low value of positronium intensity owing to elimination of trapped electrons. Slowing down the growth of positronium intensity with prolonged positron irradiation is ascribed to inhibiting action of radicals. (C) 2004 Elsevier B.V. All rights reserved.

  33. Goworek, T. Zaleski, R. Wawryszczuk, J., Odd-even differences in o-Ps properties in some solid long- chain alkanes, Positron Annihilation, Icpa-13, Proceedings, (), 2004, 298-300

    Positron lifetime spectra in solid long-chain alkanes were measured as a function of the storage time with positron source between the samples, and as a function of temperature and pressure, Large differences of the time constant of I-3 increase were observed for odd-numbered and even-numbered molecules. High pressures also induced the I-3 instability, but in this case the I-3 intensity decreased. In the rigid solid phase the o-Ps lifetime in even-numbered alkanes was shorter than in odd ones, which was due to different thickness of the empty layer between the lamellas in the crystal structure.

  34. Zaleski, R. Borowka, A., Positron study of MCM-41 sieve formation, Positron Annihilation, Icpa-13, Proceedings, (), 2004, 364-366

    The removal of alkyltrimethylammonium template from MCM-41 ordered silica was investigated, using positron annihilation lifetime spectroscopy (PALS). The lifetime spectra of positrons were measured as a function of temperature for several samples with different template alkyl chain length (different pore radius). At low temperatures the template interior behaves like a liquid, and the "bubble model" of positronium in liquid can be applied. The change of template structure starts at 380-400 K, and at 520 K the process of template removal is completed. Analysis of o-Ps lifetime components suggests the following stages: breaking long micelle cylinders, rise of the gaps between the fragments, and pore evacuation.

  35. Goworek, T. Zaleski, R. Wawryszczuk, J., Temperature, pressure and source-irradiation effects in positronium formation in some solid long-chain alkanes, Chemical Physics, 295(3), 2003, 243-253

    Positron lifetime spectra in solid n-alkanes C19H40, C20H42 and C21H44 were measured. The effect of irradiation by positron source (increase of ortho-positronium intensity I-3), known from polymer studies, was found to appear also in alkanes; at about 100 K it can lead to doubling the intensity. The time constant of I-3 rise in n-eicosane increased with temperature, reaching the value of 60 h, while it decreased (down to 1 h) in its odd-numbered neighbours. The difference in ortho-Ps lifetimes between odd- and even-numbered alkanes can be explained by different thickness of interlamellar layer in the crystal structure. The variation of I-3 after application of high pressure was also observed, but in this case the intensity decreased with time. (C) 2003 Elsevier B.V. All rights reserved.

  36. Goworek, T. Wawryszczuk, J. Zaleski, R., Ortho-Ps annihilation in resorcinol at high pressure, Radiation Physics and Chemistry, 68(3-4), 2003, 577-579

    The effect of high pressure on positron lifetime spectra in resorcinol was investigated. The o-Ps lifetime decreases with pressure continuously reaching the value which needs redefinition of DeltaR value used in the Tao-Eldrup model. The intensity of long-lived component unexpectedly rises with pressure increase, but it 450 MPa a drop of that intensity can indicate the approach of the minimal size of free volume able to trap Ps. preliminary data for hydroquinone are also presented. (C) 2003 Elsevier Ltd. All rights reserved.

  37. Zaleski, R. Wawryszczuk, J. Borowka, A. Goworek, J. Goworek, T., Temperature changes of the template structure in MCM-41 type materials; positron annihilation studies, Microporous and Mesoporous Materials, 62(1-2), 2003, 47-60

    The lifetime spectra of positrons annihilating in MCM-41 ordered silica were measured as a function of temperature. It was found that in alkyltrimethylammonium templates degradation in vacuum begins at 380-400 K, that consists in breaking the long micelle cylinders, rise of gaps between the fragments and finally pore evacuation. The latter process is not completed and particularly in C12TAB the spectrum component belonging to fragmented template preserves its high intensity up to 520 K (the highest temperature in our experiment). The pore surface area over 1000 m(2)/g is achieved already at temperatures about 490 K. The lifetime of the longest-lived component indicates that practically all ortho-positronium, atoms leave the pores before annihilation. (C) 2003 Elsevier Inc. All rights reserved.

  38. Zaleski, R. Wawryszczuk, J. Goworek, J. Borowka, A. Goworek, T., Vacuum removal of the template in MCM-41 silica studied by the positron annihilation method, Journal of Colloid and Interface Science, 262(2), 2003, 466-473

    Positron annihilation lifetime spectra were measured for ordered silica before template (octadecyltrimethyl ammonium) removal. An intermediate lifetime component, well pronounced in the spectra, indicates the presence of structural defects in the template being the size of a surfactant molecule. At the temperature near 420 K a radical change of template structure occurs, consisting in appearance of disorder and the degradation of template; evaporation of the fragments begins. It seems that moderate heating (up to about 500 K only) in vacuum for several hours is an effective and simple method of template removal, leaving no pure carbon residue in the pore structure. The results are compared with the data from the liquid nitrogen adsorption/desorption method and elemental analysis, confirming the positron annihilation results. (C) 2003 Elsevier Science (USA). All rights reserved.

  39. Zaleski, R. Borowka, A. Wawryszczuk, J. Goworek, J. Goworek, T., Positron probing of the micellar template interior in MCM-41, Chemical Physics Letters, 372(5-6), 2003, 794-799

    The properties of positronium annihilating in the micellar template in MCM-41 materials were investigated. For alkyltrimethylammonium bromide surfactants (C-n = 14,16,18) the template interior is liquid-like; the bubble model of positronium, elaborated for bulk liquids, can be applied. The equivalent surface tension is linearly dependent on temperature, like in classic liquids. A very long-lived component in o-Ps lifetime spectrum (approximate to 20 ns) can be ascribed to o-Ps in cracks in the elongated template structure. (C) 2003 Elsevier Science B.V. All rights reserved.

  40. Zaleski, R. Wawryszczuk, J. Goworek, T., Electron density at positron's site in MCM-41 ordered silica, Chemical Physics Letters, 372(5-6), 2003, 800-804

    The lifetime of para-positronium in raw materials of MCM-41 class was measured as a function of temperature. It was found that the lifetime shortens when the template filling is removed and empty pores are created. Rough data are given also for phase transition in n-nonadecane. The electron contact density eta on the positron bound into positronium atom in the condensed media, determined in experiments, seems to be related more to the size of positronium trap than to the electronic properties of the medium. The role of contact density eta in the estimation of ortho-positronium lifetime in the bulk is discussed. (C) 2003 Elsevier Science B.V. All rights reserved.

  41. Wawryszczuk, J. Goworek, J. Zaleski, R. Goworek, T., Positron lifetime in mesoporous silica of MCM-41 type, Langmuir, 19(7), 2003, 2599-2605

    Positron lifetime spectra in ordered mesoporous silica were measured. In the raw material (still containing the template) the voids in micellae reaching 1 nm in size were observed. Ortho-positronium (o-Ps) lifetime was found to be very sensitive to the carbon deposits left in pores after pyrolysis. In highly dispersed materials the relation between the pore diameter and positronium lifetime is shadowed by o-Ps escape from the pores to extragranular spaces. A very slow thermalization of o-Ps and increased lifetime of free positrons in low-density bulk were also observed.

  42. Wawryszczuk, J. Zaleski, R. Goworek, T., Positron studies of vapour absorption and desorption by melamine-formaldehyde resin, Materials Chemistry and Physics, 76(3), 2002, 285-289

    The lifetime spectra of positrons annihilating in vapour- absorbing polymers were measured in order to gain information about the change of dimensions and number of free volume holes during absorption and desorption. Absorption of water, methanol and ethanol vapours in melamine-formaldehyde resin leads to the shortening of ortho-positronium lifetime that can be explained by predominant filling larger holes by absorbed molecules, leaving smaller ones empty and accessible for ortho- positronium. Removal of molecules by outpumping the vapour increases the lifetime. It was found that the intensity of positronium formation does not follow the rule of proportionality to the number of free volume sites. (C) 2002 Elsevier Science B.V. All rights reserved.

  43. Goworek, T. Jasinska, B. Wawryszczuk, J. Zaleski, R. Suzuki, T., On possible deviations of experimental PALS data from positronium pick-off model estimates, Chemical Physics, 280(3), 2002, 295-307

    The sources of possible inconsistency between the models of trapped positronium annihilation and experimental data are discussed. There are two such sources: excessive simplifications in the models of pick-off process and appearance of other processes not accounted in the models. In the case of the smallest traps, the penetration depth of ortho- positronium (o-Ps) wavefunction into the bulk can be larger than usually assumed. In traps of sizes exceeding I run the population of excited levels in the well has to be taken into account. For such large voids the sources of divergence of the experiment and model predictions can be: escape of o-Ps from open pores to outside, chemical interaction of o-Ps with pore surfaces (adsorbate layers), the presence of impurities inside free volumes. (C) 2002 Elsevier Science B.V. All rights reserved.

  44. Goworek, J. Wawryszczuk, J. Zaleski, R., Porosity of ordered silica materials by nitrogen adsorption and positronium annihilation lifetime spectroscopy, Journal of Colloid and Interface Science, 243(2), 2001, 427-432

    The present paper is devoted to the synthesis and textural characterization of silica materials. The mixed silica sample was composed of Si-100 silica gel with small agglomerates of MCM41 molecular sieve deposited on its surface. MCM41 mesoporous silicates were synthesized using octadecyl trimethylammonium bromide. Using a new synthesis procedure it was possible to prepare silica containing three groups of mesopores. The recently developed positronium annihilation lifetime spectroscopy method for characterization of mesoporous materials was applied ro the investigated silica materials. The results were compared with those from the nitrogen desorption method. The current studies demonstrate moderate consistency of pore size characteristics obtained by using various techniques. (C) 2001 Academic Press.

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