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1
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Free-Volume Studies in Polycaprolactone/Poly(propylene oxide) Urethane/Urea Membranes by Positron Lifetime Spectroscopy

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Ferreira Marques M., Gordo P., de Lima A., Queiroz D., Norberta de Pinho M., Major P., Kajcsos Z.
Acta Physica Polonica A
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2008
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vol. 113
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issue 5
1359-1364
EN
Positron annihilation lifetime spectroscopy was used to study the free volume parameters in polypropylene oxide-based tri-isocyanate terminated prepolymer/polycaprolactone diol bi-soft urethane/urea membranes (PU/PCL) with PCL content from 5 up to 25 wt%. Positron annihilation lifetime spectroscopy measurements carried out in the temperature range 298-324 K mirrored the phase separation of the various soft and hard segments present in the membranes. The size and amount of free volume holes determined by positron annihilation lifetime spectroscopy appear to be correlated with the CO_2 gas permeability through the membranes.
2
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Positrons and Positronium Atoms in a Condensed Phase Close to Its Melting Point

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Stepanov S., Zvezhinskiy D., Byakov V., Duplâtre G., Stepanov P.
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vol. 125
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issue 3
691-695
EN
Investigation of the local heating effect at the terminal part of a fast positron track sheds light on the accumulation of defects in a frozen medium close to its melting point. Estimations of the formation energies of the structural defects which may trap the Ps atom as well as a contribution of these defects to the enthalpy of fusion are obtained.
3
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Is Kapton Really That Simple?

100%
Dauwe C., De Baerdemaeker J., Van Waeyenberge B., Djourelov N., Laforest N.
Acta Physica Polonica A
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2008
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vol. 113
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issue 5
1315-1319
EN
Age momentum correlation experiments in kapton has revealed the existence of two positron states corresponding to the trapping of positrons on the partially negatively charged O and/or N sites in the polymer chain. A young age broadening of the annihilation line shape is also observed and is attributed to the annihilation in flight of the positrons.
4
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Positron and Positronium Annihilation in Polymers Studied by Age-Momentum Correlation Spectroscopy

100%
Sato K., Murakami H., Ito K., Hirata K., Kobayashi Y.
Acta Physica Polonica A
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2008
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vol. 113
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issue 5
1511-1516
EN
Positron (e⁺) and positronium (Ps) annihilation processes in polymers are studied by positron age-momentum correlation spectroscopy, which can sensitively probe momentum distributions of e⁺, p-Ps, and o-Ps. For polyether sulfone and ethylene tetrafluoroethylene copolymer belonging to oxygen-containing polymers (O group) and fluorine-containing polymers (F group), respectively, significant effects of positron trapping by polar element are observed. The Doppler profile of o-Ps pick-off annihilation is strongly influenced by F atoms, giving rise to anomalous broadening. The results are discussed together with our previous data of the S-I₃ correlation in order to explore the feasibility of chemical analysis around the free volumes by age-momentum correlation spectroscopy.
5
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The Evidence of Quasi-Free Positronium State in GiPS-AMOC Spectra of Glycerol

100%
Zvezhinskiy D., Butterling M., Wagner A., Krause-Rehberg R., Stepanov S.
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vol. 125
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issue 3
821-824
EN
We present the results of processing of age-momentum correlation spectra that were measured for glycerol by the gamma-induced positron spectroscopy facility. Our research has shown that the shape of experimental s(t) curve cannot be explained without introduction of the intermediate state of positronium (Ps), called quasi-free Ps. This state yields the wide Doppler line near zero lifetimes. We discuss the possible properties of this intermediate Ps state from the viewpoint of developed model. The amount of annihilation events produced by quasi-free Ps is estimated to be less than 5% of total annihilations. In the proposed model, quasi-free Ps serves as a precursor for trapped Ps of para- and ortho-states.
6
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Application of Coincidence Doppler Broadening Spectroscopy to Hydrocarbons at Different Substance States

100%
Yu R., Suzuki T., Ito Y., Djourelov N., Kondo K., Shantarovich V.
Acta Physica Polonica A
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2005
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vol. 107
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issue 4
697-701
EN
Coincidence Doppler broadening spectroscopy was applied to study n-hexane (C_6H_{14}), cyclohexane (C_6H_{12}) and cyclohexanone (C_6H_{10}O), at solid, as well as liquid states. The experiments were performed in parallel with traditional positron annihilation lifetime spectroscopy. Significant positron trapping by oxygen was observed in cyclohexanone; the oxygen effect is stronger in liquid state than in solid one, which can possibly be attributed to positron solvation in polar solution. Coincidence Doppler broadening results for n-hexane and cyclohexane indicate an existence of higher energetic annihilation electrons in Ps-bubble forming liquids than that in solids.
7
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Chemical Information of Chitosan-Based Complex Extracted from Coincidence Doppler Broadening Spectra

100%
Cao X., Xia R., Yang J., Zeng M., Wang B., Yu R., Wei L.
Acta Physica Polonica A
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2017
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vol. 132
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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.
8
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Formation of Quasi-Free and Bubble Positronium States in Water and Aqueous Solutions

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Stepanov S., Duplâtre G., Byakov V., Zvezhinskiy D., Subrahmanyam V.
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vol. 125
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issue 3
770-774
EN
It is shown that in aqueous solutions a positronium atom is first formed in the quasi-free state, and, after 50-100 ps, becomes localized in a nanobubble. Analysis of the annihilation spectra of NaNO_3 aqueous solutions shows that the hydrated electron is not involved in the positronium (Ps) formation.
9
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Application of Positron Spectroscopy for the Detection of Nanostructures in Water-Alcohol Mixtures

100%
Stepanov P., Byakov V., Zaluzhnyi A.
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vol. 125
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issue 3
767-769
EN
Analysis of the o-Ps lifetimes concentration dependences in water-propanol mixtures (with and without CoCl_2 additive) shows that this mixture looks like an emulsion of alcohol micelles in water at propanol mole fractions 0.1-0.4.
10
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A New Approach to the Presentation of the Positron Annihilation Lifetime Spectroscopy Results, n-Alkanes

100%
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.
11
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Content available

Molecular Structure of Water-Like Positronium Complexes

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Rolim F., Mohallem J.
Acta Physica Polonica A
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2005
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vol. 107
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issue 4
661-665
EN
We resort to a previously introduced molecular model for positron complexes to study the molecular structures of Ps_2O and PsOH and to explore their analogies and differences from the molecular structure of water.
12
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Is a Molecular Adiabatic Approximation Appropriate to Positronic Atoms and Molecules?

100%
Mohallem J.
Acta Physica Polonica A
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2008
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vol. 113
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issue 5
1465-1469
EN
The adiabatic approximation to positronic atoms and molecules was considered as an option to the computationally unfeasible methods that treat all particles in a common footing, in two different approaches communicated in the 37th PSPA. Here we present further assessment and comparison of the two approaches as a way of evaluating the potential of adiabatic or, as we found preferable, molecular approaches.
13
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Positron Annihilation Lifetime Analysis of Left- and Right-Handed Alanine Single Crystals

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Eren B., Wu F., Eren E., Jean Y., Van Horn J.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1456-1460
EN
Studies of the interaction of polarized light or particles (including electrons, e¯, or positrons, e⁺) with asymmetric forms of matter has been of interest to scientists since the discovery of chirality and the subsequent development of particle physics. Researchers have been interested in e⁺ interactions with chiral molecules for decades, but with mixed and indecisive results. After reviewing the field, we speculated that the e⁺ or positronium (Ps) might interact differently with chiral pairs of large single crystals, i.e., the left-handed or right-handed asymmetric forms of the crystals - and subsequently observed significant differences in "free positron" annihilation and intensities in the evaluation of left-handed or right-handed quartz single crystals. This result may be understood to be a "particle stereorecognition" phenomenon. To extend this line of inquiry we crystallized mm scale L- or D-alanine crystals and performed positron annihilation lifetime spectroscopy measurements using a ²²Na positron source. Alanine crystals were obtained via slow evaporation of water in a Dewar, or from water/acetone solvent in a temperature-controlled environment. These methods resulted in small ( ≈0.5 cm/side) or large ( ≥1.0 cm/side) crystals, respectively. While some intensity (I₂) results from left-handed and right-handed crystals varied in positron annihilation lifetime spectroscopy analysis, the errors associated with the measurements do not indicate a stereorecognition of alanine via positron interactions.
14
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Positronium Formation in Organic Liquids

100%
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.
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