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1
Content available Positrons in naphthalene : critical remarks on the relation between o-Ps lifetime and void size
Goworek T., Zgardzińska B., Wawryszczuk J.
Nukleonika
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2013
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Vol. 58, No. 1
183-187
EN
Lowering the temperature or applying high pressure leads to elimination of positronium component in the e+ lifetime spectrum in solid naphthalene. Disappearance of positronium means reaching the free volume size limit at which there is no energy level in the potential well. It allows to estimate that size, which is found inconsistent with predictions of the popular Tao-Eldrup model. The range of applicability of that model is discussed. The dependence of the free e+ decay constant on pressure indicates that positronium is formed not only in the blob processes, but during the whole free positron life. The lifetime of free positrons begins to rise with temperature earlier than Ps intensity.
2
Content available Positron annihilation lifetime spectroscopy study of thermal processing and rehydration of dry leek (Allium porrum L.)
Zaleski R., Wawryszczuk J., Sobczak K.
Nukleonika
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2010
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Vol. 55, No. 1
73-78
EN
New application of positron annihilation lifetime spectroscopy (PALS) to development of food processing techniques is tested. Dehydrated leeks were an object of the study. Three experiments were performed consisting of evacuating air and volatile compounds from the sample, applying thermal treatment and rehydrating the sample. Distinct changes in positron lifetime spectra allowed the monitoring of alterations in the sample structure. The most likely origin of the particular components present in the spectra was able to be proposed from these data. Changes of the components were ascribed to the various processes occurring in the samples.
3
Content available Electron traps in long-chain alkanes
Pietrow M., Wawryszczuk J.
Nukleonika
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2010
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Vol. 55, No. 1
51-55
EN
Positron lifetime spectra in long-chain alkanes were measured at various wavelengths of light illuminating the samples as a function of temperature, storage time. It was found that in n-alkanes with carbon chain longer than 30 atoms two kinds of electron traps exist; the depth of shallower of them is less than 0.52 eV. They are discharged already at a temperature of 120 K.
4
Content available remote Pore size determination by positron annihilation lifetime spectroscopy
Jasińska B., Dawidowicz A. L., Goworek T., Wawryszczuk J.
Optica Applicata
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2003
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Vol. 33, nr 1
7-12
EN
Two Vycor glasses were investigated using PALS method. The model of pick-off annihilation in cylindrical free volume was applied to evaluate the pore radii. The o-Ps mean lifetime value in the pores changed from 6.5 to 40 ns in one glass, while from 13 to 51 ns in the other (softer) one. The determined pore radii, using a cylindrical shape model, were from 0.5 to 1.4 nm and from 0.7 to 1.6 nm, respectively.
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