Do the CONTIN or the MELT programs accurately reveal the o-Ps lifetime distribution in polymers? Analysis of experimental lifetime spectra of amorphous polymers

Abstract. Two different classes of molecular crystals were investigated. The fi rst group was benzenediols, which are characterized by the same chemical composition but a different organization of their crystallographic structures; all of the compounds from this group have only one kind of free volumes. The second class was represented by olanzapine, which has more complex chemical composition and two kinds of free volumes in the structure. The o-Ps lifetime values determined from positron annihilation lifetime spectroscopy (PALS) measurements agree quite well with those calculated for sizes found from crystallographic data for benzenediols (agreement within 10% of the lifetime values). For olanzapine, a good agreement is observed in the case of cuboidal free volumes, while for the other kind of void, the agreement is less satisfactory. Positronium diffusion coeffi cient determined from o-Ps redistribution in olanzapine agrees with these found for polymers.

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“…5a). This effect was stated and well described [16,17] in literature and appears also in simulated spectra containing only one lifetime value.…”

Section: Resultssupporting

confidence: 79%

Comparison of the free volume sizes and shapes determined from crystallographic and PALS data

Tydda

Jasińska

2015

Nukleonika

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“…The meaning of the shorter one τ (1) o−Ps is still uncertain. It may be due to the statistical splitting-up of a distribution of hole sizes [6], or to a Ps attached to a molecule of the polymer. Details of the fitting procedure were given by [1,5].…”

Section: Discussionmentioning

confidence: 99%

Experimental Verification of the Blob Model and Delayed Formation of Ps

2005

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blob model for the formation of positronium can be considered as an extension of the spur model. However, it offers many extra possibilities and is more sound from the radiation chemistry point of view. A full coding of this model leads to non-exponential lifetime spectra, and standard multi-component analysis is no longer adequate for materials such as polymers. Age momentum correlation experiments were performed on linear PMMA at different temperatures and were analyzed with the non-exponential blob model. We show the adequacy of this model, and moreover an alternative explanation for the young-age broadening and delayed formation of positronium.

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“…Deconvolution was adapted for positron lifetime spectra analysis in MELT routine [4]. There is also a method of deconvolution by numerical Laplace inversion (CONTIN program [3]), but it was found that results of MELT are more accurate [9]. Applying MELT to typical lifetime spectra where a lifetime spectrum is registered in thousands of channels, demands quite large routine's requirements for computer memory (about 2 GB for a spectrum in 7000 channels) and CPU speed (a few minutes on 3.2 GHz CPU for the same spectrum).…”

Section: Methods Of Numerical Analysismentioning

confidence: 99%

“…The results were shown in the same figures in comparison. However, it is known that MELT has a tendency to split a wide distribution of lifetimes into two narrower ones for polymers [6,9]. In order to test this effect in the range of long lifetimes the spectrum was simulated assuming a wide lognormal dispersion of lifetimes.…”

Section: Remarks On Meltmentioning

confidence: 99%

Measurement and Analysis of the Positron Annihilation Lifetime Spectra for Mesoporous Silica

Zaleski

2006

Acta Phys. Pol. A

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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.

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Do the CONTIN or the MELT programs accurately reveal the o-Ps lifetime distribution in polymers? Analysis of experimental lifetime spectra of amorphous polymers

Cited by 42 publications

References 6 publications

Comparison of the free volume sizes and shapes determined from crystallographic and PALS data

Comparison of the free volume sizes and shapes determined from crystallographic and PALS data

Experimental Verification of the Blob Model and Delayed Formation of Ps

Measurement and Analysis of the Positron Annihilation Lifetime Spectra for Mesoporous Silica

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