Generation of Positronium Annihilation Lifetime Spectra in Polymers
journal of kerbala university,
2007, Volume 3, Issue 3, Pages 152-158
AbstractPositronium annihilation lifetime spectroscopy is a powerful prope that ia used in the study of free volume in polymers. In this work we study the positronium annihilation lifetime spectra in polymers contain free volume and in pure polymers. The spectra that generated contain single Gaussian component fixed at 400ps convoluted with three lifetime components (τ1,τ2 and τ3) and considering τ1 originated from annihilation of para-positronium, τ2 originated from annihilation of positrons in matter and τ3 originated from annihilation of ortho-positronium in free volume also the background fixed at 0.001% of peak. Also study the effect of mean value of free volume size and its concentrations by study the effect of intensity of long-lived component (I3) the theoretical spectra were compared with experimental spectra for polystyrene sample and we discussed the differences. We notice that as the long-lived component increase the right hand side of the spectrum rise. The difference between the experimental spectrum and the generated spectrum arises from that the background and time-zero channel in the generated spectra considered to be constant, but in experimental spectra, these parameter varied with thermal influences. Moreover the generated spectra described by single Gaussian component. The separating of 0.1 ns difference in lifetime components give specific description for positronium annihilation lifetime in polymers, also the difference of 5% in intensity give distinguished separating in the spectra, and these give distinguished components which have small intensities in experimental spectra . There are clear difference between positronium annihilation lifetime spectrum in pure polymers and positronium annihilation lifetime in defective polymers (contain free volume), this due to the effect of concentration and size of free volume on the spectrum. The small resolution (400ps) give a clear separation in smallest lifetime components (τ1 ,τ2 ) and smallest intensities in the generated spectra.
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