72 research outputs found
Beyond the Point Ps Approximation
In application to positron annihilation spectroscopy, Ps atom is considered
not as a point particle, but as a finite size e+ e- pair localized in a
bubble-state in a medium. Variation of the internal Coulombic e+ -e- attraction
vs. the bubble radius is estimated
Formation of quasi-free and bubble positronium states in water and aqueous solutions
It is shown that in aqueous solutions a positronium atom is first formed in
the quasi-free state, and, after 50-100 ps, becomes localized in a nanobubble.
Analysis of the annihilation spectra of NaNO3 aqueous solutions shows that the
hydrated electron is not involved in the positronium (Ps) formation
Lamb wave ultrasonic evaluation of welded AA2024 specimens at tensile static and fatigue testing
The paper deals with the investigation of Lamb waves ultrasonic testing technique applied for evaluation of different stress-strain and damaged state of aluminum specimens at static and fatigue loading in order to develop a Structural Health Monitoring (SHM) approach. The experimental results of tensile testing of AA2024T3 specimens with welded joints are presented. Piezoelectric transducers used as actuators and sensors were adhesively bonded to the specimen's surface using two component epoxy. The set of static and cyclic tensile tests with two frequencies of acoustic testing (50 kHz and 335 kHz) were performed. The recorded signals were processed to calculate the maximum envelope in order to evaluate the changes of the stress-strain state of the specimen and its microstructure during static tension. The registered data are analyzed and discussed in terms of signal attenuation due to the formation of fatigue defects during cyclic loading. Understanding the relations between acoustic signal features and fatigue damages will provide us the ability to determine the damage state of the structure and its residual lifetime in order to design a robust SHM system
Positronium in a liquid phase: formation, bubble state and chemical reactions
This chapter reviews the following items: 1. Energy deposition and track
structure of fast positrons: ionization slowing down, number of ion-electron
pairs, typical sizes, thermalization, electrostatic interaction between e+ and
its blob, effect of local heating; 2. Positronium formation in condensed media:
the Ore model, quasifree Ps state, intratrack mechanism of Ps formation; 3.
Fast intratrack diffusion-controlled reactions: Ps oxidation and ortho-para
conversion by radiolytic products, reaction rate constants, interpretation of
the PAL spectra in water at different temperatures; 4. Ps bubble models.
"Non-point" positronium: wave function, energy contributions, relationship
between the pick-off annihilation rate and the bubble radius
- β¦