Positronium Fractions and Cavity Sizes Derived from 1- and 2-Detector Doppler Broadening Spectra Positronium Fractions and Cavity Sizes Derived from 1- and 2-Detector Doppler Broadening Spectra

Garcı́a, A Alba; Siebbeles, L. D. A.; Rivera, Alejandro; Schüt, H.; Eijt, S.W.H.; Galindo, R. Escobar; Veen, A. van

doi:10.4028/www.scientific.net/msf.363-365.287

Cited by 8 publications

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“…It is possible to obtain the p-Ps intensity by utilizing a multi-Gaussian fitting [17][18][19] of Doppler broadening spectrum using the ACARFIT program included in the PATFIT package. 7 In order to check the reliability of multi-Gaussian fitting to obtain p-Ps intensity, we measured a series of polymer samples using both CDB and conventional positron lifetime measurements.…”

Section: Coincidence Doppler Broadening Measurementsmentioning

confidence: 99%

Spin conversion of positronium inNiO/Al2O3catalysts observed by coincidence Doppler broadening technique

et al. 2010

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High-purity NiO/ Al 2 O 3 catalysts were prepared by mixing NiO and ␥-Al 2 O 3 nanopowders. X-ray diffraction patterns were measured to characterize the grain size and crystalline phase of the nanopowders. Positronannihilation spectroscopy was used to study the microstructure and surface properties of the pores inside the NiO/ Al 2 O 3 catalysts. The positron lifetime spectrum comprises two short and two long lifetime components. The two long lifetimes 3 and 4 correspond to ortho-positronium ͑o-Ps͒ annihilated in microvoids and large pores, respectively. With increasing NiO content in the NiO/ Al 2 O 3 catalysts, both 4 and its intensity I 4 show continuous decrease. Meanwhile, the para-positronium ͑p-Ps͒ intensity, obtained from coincidence Doppler broadening spectra, increases gradually with NiO content. The different variation in o-Ps and p-Ps intensity suggests the ortho-para conversion of positronium in NiO/ Al 2 O 3 catalysts. X-ray photoelectron spectroscopy shows that Ni mainly exists in the form of NiO. The electron-spin-resonance measurements reveal that the ortho-para conversion of Ps is induced by the unpaired electrons of the paramagnetic centers of NiO.

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Section: Coincidence Doppler Broadening Measurementsmentioning

confidence: 99%

Spin conversion of positronium inNiO/Al2O3catalysts observed by coincidence Doppler broadening technique

et al. 2010

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“…The determination of this factor depends on the measurement of a sample with 100% o-Ps selfannihilation as presented in [15] but for our qualitative disccusion we will omit this. As a first approximation we assume that the pick-off process is described with the same S and W parameters as the bulk annihilation [16]. Then, the experimental results can be interpreted in terms of a and b fractions (see Table 2).…”

Section: Resultsmentioning

confidence: 99%

Systematic positron study of hydrophilicity of the internal pore surface in ordered low-k silica thin films

Galindo

Veen

Schüt

et al. 2003

Materials Science and Engineering: B

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“…However, these effects are smaller than for the case of direct positron annihilation. The Doppler broadening and angular correlation of the radiation produced by annihilation of p-Ps can provide information on the size and shape of voids in materials. , The total spin angular momentum of o-Ps is equal to one and in vacuum conservation of spin angular momentum makes annihilation of o-Ps into three γ-quanta the only possible decay channel. In a vacuum, this process occurs with a lifetime of 142 ns.…”

Section: Introductionmentioning

confidence: 99%

Positronium Formation Dynamics in Radiolytic Tracks: A Computer Simulation Study

et al. 2002

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Positron track structures were simulated by stochastic modeling of the collision-by-collision slowing down of positrons in n-hexane. The details of the inelastic scattering of positrons and of electrons produced in ionizing collisions were taken into account until the particle energies had degraded to less than 25 eV. Further slowing down to thermal energy was assumed to result in a spherically symmetric thermalization distribution around the position where the particle energy becomes less than 25 eV. The dynamics of positronium formation in competition with electron-cation recombination and positron annihilation was followed by a simulation of the diffusive motion of the charged species in each other's Coulomb field. Positronium formation was found to involve reaction of the thermalized positron with electrons produced along the last few hundred nm of its track-end, corresponding to several keV of energy attenuation. Positronium formation occurs mainly during the first few tens of picoseconds after positron implantation and extends to hundreds of picoseconds. Simulation reproduces the experimental positron lifetime spectra reported in the literature. The experimentally reported electric-field dependence of the ortho-positronium yield in liquid n-hexane could be reproduced with an exponentially decaying positron thermalization distribution with a mean distance of 50 nm, while a Gaussian positron thermalization distribution was found to be inappropriate.

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Positronium Fractions and Cavity Sizes Derived from 1- and 2-Detector Doppler Broadening Spectra Positronium Fractions and Cavity Sizes Derived from 1- and 2-Detector Doppler Broadening Spectra

Cited by 8 publications

References 0 publications

Spin conversion of positronium inNiO/Al2O3catalysts observed by coincidence Doppler broadening technique

Spin conversion of positronium inNiO/Al2O3catalysts observed by coincidence Doppler broadening technique

Systematic positron study of hydrophilicity of the internal pore surface in ordered low-k silica thin films

Positronium Formation Dynamics in Radiolytic Tracks: A Computer Simulation Study

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