Positron lifetimes annihilation

Spectroscopy, 490. See also 13C NMR spectroscopy FT Raman spectroscopy Fourier transform infrared (FTIR) spectrometry H NMR spectroscopy Infrared (IR) spectroscopy Nuclear magnetic resonance (NMR) spectroscopy Positron annihilation lifetime spectroscopy (PALS) Positron annihilation spectroscopy (PAS) Raman spectroscopy Small-angle x-ray spectroscopy (SAXS) Ultraviolet spectroscopy Wide-angle x-ray spectroscopy (WAXS)... 

In this work positron annihilation lifetime spectroscopy (PALS) was used to investigate structural diversity inside zeolite precursor matrix caused by the presence of alkali cations Na, K, Rb and Cs. PALS is an established and well-proven method for structural investigations of various materials, extensively used for metals and alloys, semiconductors and porous materials [3, 4]. In the investigations of zeolites PALS has been mostly used for their void structure and size study [5, 6, 7, 8], also in correlation to... 

Positron annihilation lifetime spectroscopy (PALS) provides a method for studying changes in free volume and defect concentration in polymers and other materials [1,2]. A positron can either annihilate as a free positron with an electron in the material or capture an electron from the material and form a bound state, called a positronium atom. Pnra-positroniums (p-Ps), in which the spins of the positron and the electron are anti-parallel, have a mean lifetime of 0.125 ns. Ortho-positroniums (o-Ps), in which the spins of the two particles are parallel, have a mean lifteime of 142 ns in vacuum. In polymers find other condensed matter, the lifetime of o-Ps is shortened to 1-5 ns because of pick-off of the positron by electrons of antiparallel spin in the surrounding medium. 

Positron annihilation lifetime measurements have been performed on float-zone Si at high teipperatures and show that vacancy-like defects are formed (20). 

Lozano-Castello D, Cazorla-Amoros D, Linares-Solano A, Hall PJ, and Fernandez JJ. Characterization of activated carbon fibers by positron annihilation lifetime spectroscopy (PALS). In Unger KK, et al., eds. Studies in Surface Science and Catalysis, Characterisation of Porous Solids V, vol. 128, the Netherlands Elsevier Science. 2000 523-532. 

Independent of whether or not a well-defined crossover temperature can be observed in NS data above Tg, it has been well known for a considerable time that on heating a glass from low temperatures a strong decrease of the Debye-Waller factor, respectively Mossbauer-Lamb factor, is observed close to Tg [360,361], and more recent studies have confirmed this observation [147,148,233]. Thus, in addition to contributions from harmonic dynamics, an anomalously strong delocalization of the molecules sets in around Tg due to some very fast precursor of the a-process and increases the mean square displacement. Regarding the free volume as probed by positron annihilation lifetime spectroscopy (PALS), for example, qualitatively similar results were reported [362-364]. 

The main techniques used are positron annihilation lifetime spectroscopy (PALS) and the Doppler broadening (DB) or angular correlation (AC) techniques. The PALS parameters are the relative intensities (I j) and the... 

Suzuki, R., Ohdaira, T., Shioya, Y. and Ishimaru, T. (2001) Pore characteristics of low-dielectric-constant films grown by plasma-enhanced chemical vapor deposition studied by positron annihilation lifetime spectroscopy , Jpn. J. Appl. Phys. 40, L414. 

Petkov, M. P., Weber, M. H., Lynn K.G. and Rodbell, K. P. (2000) Probing capped and uncapped mesoporous low-dielectric constant films using positron annihilation lifetime spectroscopy , Appl. Phys. Lett. 77, 2470. 

Gregory, R.B. and Zhu, Y. (1990) Analysis of positron annihilation lifetime data by numerical laplace inversion with the program CONTIN , Nucl. Instrum. Methods Phys. Res., Sect. A 290,1172. 

The aim of this chapter is to introduce the reader to the application of positron annihilation techniques to polymers. An extensive review of the large volume of publications related to positron studies in polymers will not be presented. Rather it is intented to introduce the reader to the theory and techniques used in polymer studies and indicate the types of information that can be obtained about different polymer systems. The main focus of this chapter will be on the use of positron annihilation lifetime spectroscopy (PAL) in polymer studies. Chapter 11 discusses the use of monoenergetic slow positron beams used to study polymers surfaces. One of the interesting new developments in the application of positron annihilation techniques in polymers is the positron age-momentum correlation technique (AMOC). This technique promises to shed new light on the mechanisms of positronium formation and annihilation in polymer systems. A more detailed discussion of this technique can be found elswhere in this text. 

The analysis of the positron annihilation lifetime spectra is a very important aspect of using the PAL techniques to analyze polymers. Without proper data analysis interpretation of data might be misleading and important scientific information will be lost. In PAL studies of polymers the PAL spectrum can be analyzed in two ways (1) a finite lifetime analysis or (2) continuous lifetime analysis. In the finite lifetime analysis the PAL spectra is resolved into a finite number of negative exponentials decays. The experimental data y(t) is expressed as a convoluted expression (by a symbol ) of the instalment resolution function R(t) and a finite number (n) of negative exponentials ... 

Figure 13.11 Positron annihilation lifetime spectra for porous MSQ films generated by mixing MSQ film with different triblock copolymers PI 03, F88, P105, and F38. A spectrum for non-porous MSQ is listed for comparison [28].

Kristiak, J., Bartos, J., Fristiakova, K., Sausa, O., Bandzuch, P. (1994) Free-volume microstructure of amorphous polycarbonate at low temperatures determined by positron-annihilation-lifetime spectrospcopy . Phys. Rev.B. 49(10), 6601. 

Forsyth, M., Meakin, P., MacFarlane, D.R., Hill, A.J. (1993) Positron annihilation lifetime spectroscopy as a probe of free volume in plasticized solid polymer electrolytes . Electrochimica Acta, 40(13), 2349. 

Positron annihilation lifetime measurements of free volume in wholly aromatic copolyesters and blends . Marcromolecules. 28, 6100. 

Haidar, B., Singru, R.M., Maurya, K.K., Chandra, S. (1996) Temperature dependence of positron-annihilation lifetime, free volume, conductivity, ionic mobility, and number of charge carries in a polymer electrolyte polyethylene oxide complexed with NH4CIO4 . Phys. Rev. B. 54, 7143. 

Bartos, J., Bandzuch, P., Suasa, O., Kristiakova, K., Kristiak, J., Kanaya, T., Jenninger, W. (1997) Free volume mircostructure and its relationship to the chain dynamics in cis-l,4-poly(butadiene) as seen by positron annihilation lifetime spectroscopy . Macromolecules, 30, 6906. 

Hsu, F.H., Choi, Y.J., Hadley Jr, J.H. (2000) Temperature dependence of positron annihilation lifetime spectra for polyethylene positron irradiation effects . Radiation Physics and Chemistry. 58,473. 

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