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Principles of positron porosimetry

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Zaleski R.

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tom Vol. 60, No. 4, part 1

795--800

EN

The paper deals with positron porosimetry (PP), which is based on positron annihilation lifetime spectroscopy (PALS). The numerical analysis of positron lifetime spectra for PP is more demanding than in most of other applications of PALS. The resulting intensity distributions of ortho-positronium (o-Ps) lifetimes are interpreted in terms of the extended Tao-Eldrup (ETE) model, which provides the dependence between the o-Ps lifetime and pore size. Additionally, the relation between the intensity of an o-Ps component and the pore volume allows obtaining pore size distribution (PSD). The value of the empirical parameter Δ, which is dependent on material, can be estimated from the temperature dependence of an o-Ps lifetime. The most unique feature of PP among other techniques that allow determination of PSDs is its ability to perform measurements in almost any conditions. This makes this method suitable for various in situ studies. In this review article, both the capabilities and the limitations of PP are discussed. The methods to overcome some of the limitations are presented.

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Physical activity and BMI in students beginning their studies at the Gdansk University of Physical Education and Sport in the academic year 1999/2000 and 2009/2010

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Nowak-Zaleska A. , Zaleski R. , Wilk B. , Walentukiewicz A.

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tom 05

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nr 2

EN

Background: The aim of the study was to assess physical activity undertaken by the students of Gdansk University of Physical Education and Sport in Gdansk, Poland (AWFiS) in their free time in the academic year 1999/2000 and 2009/2010 and the direction of changes in this scope. Material/Methods: Students at the Faculty of Physical Education at AWFiS were subject to research in the academic years 1999/2000 and 2009/2010. 639 students were examined (42% women, 58% men). The research was based on a diagnostic survey with an author’s own questionnaire containing questions from the scope of physical activity and participation in its forms. Results: Mean values of BMI, body weight and height were higher amongst students beginning studies in 2009/2010. The BMI in the academic year 1999/2000, both for female and male students was lower than in 2009/2010. Irrespective of the year of examinations and the gender, the majority of the respondents were characterized by DPA (declared physical activity): 60.86% of the whole sample in 1999 and 47.1% in 2009; this difference was statistically significant. In our own research a decreasing tendency of the students’ declared physical activity was observed. Percentage drop in students with GPA (great physical activity) and an increasing percentage of LPA (low physical activity) and UPA (moderate physical activity) – both in women and men. Conclusions: The year of the research was a factor diversifying the level of the respondents’ physical activity.

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Ortho-positronium migration in mesopores of MCM-41, MSF and SBA-3

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Zaleski R. , Błażewicz A. , Kierys A.

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2013

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tom Vol. 58, No. 1

235-240

EN

Three materials: MCM-41, MSF and SBA-3 with a very similar pore diameter but different lengths of cylindrical pores were investigated using the nitrogen sorption method and positron annihilation lifetime spectroscopy. The size of primary pores and interparticle spaces obtained by both methods is similar. However, volume ratios between the discussed kinds of pores found by the above-mentioned methods differ significantly. Such discrepancy is the result of both ortho-positronium migration and the inaccessibility of the pores for nitrogen. Comparing the results of nitrogen sorption and positron annihilation lifetime spectroscopy allows us to estimate that connectivity between the primary pores and the interparticle spaces is the highest in MCM-41 and lowest in SBA-3.

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Gas filling of SBA - 15 silica micropores probed by positron annihilation lifetime spectroscopy (PALS)

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Gorgol M. , Zaleski R. , Kierys A.

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2013

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tom Vol. 58, No. 1

229-233

EN

Positron annihilation lifetime measurements were conducted in situ while two gasses (nitrogen and oxygen, respectively) were introduced into the SBA-15 porous silica sample. Slow changes in lifetime spectra were observed during a long lasting gas interaction with the sample. Introduced gases slowly filled the free volumes, starting from the smallest ones, especially small micropores. In the presence of a gas, the rate of change of ortho-positronium (o-Ps) and unbound positron intensity was larger than the rate of change of lifetime. This suggests the existence of an additional process, which reduces the number of ortho-positronium atoms due to the interaction with the gas. Moreover, the process of filling pores with gas was slower than the process of emptying them while the gas was pumped out.