Development of an Electron-Positron Source for Positron Annihilation Lifetime Spectroscopy

2007 ◽  
Author(s):  
John A. Nees
Keyword(s):  
Positron Annihilation ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Positron Source ◽  
Positron Annihilation Lifetime ◽  
Electron Positron

Preliminary Positron Lifetime Results on Free Volumes in Cyclodextrins

2010 ◽  
Vol 666 ◽  
pp. 99-102 ◽  
Author(s):  
Maria Fatima Ferreira Marques ◽  
A.M.G. Moreira Da Silva ◽  
P.M. Gordo ◽  
Z. Kajcsos
Keyword(s):  
Positron Annihilation ◽  
Free Volume ◽  
Positron Lifetime ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Positron Source ◽  
Lifetime Component ◽  
Positron Annihilation Lifetime ◽  
Long Lifetime

Positron annihilation lifetime spectroscopy was used to study the free-volume parameters in various pure -, - and -cyclodextrins samples and, in the case of β-cyclodextrin, with inclusion of S-carvone and thymoquinone. The results clearly indicate the presence of long lifetime components related to Ps-formation. The data show that the addition of S-carvone to β-cyclodextrin results in a decrease of o-Ps lifetime that we ascribe to a reduction of free volume holes from 81.8 to 63.7 Å3. The long lifetime component disappears when thymoquinone is added to -cyclodextrin, indicating this substance acts as an o-Ps quencher. For all samples studied, a decrease in the long lifetime component values was observed with increasing source in situ time, a result that might be attributed to the irradiation of the sample by the 22Na positron source.

n-Nonadecane Embedded in Mesopores

2008 ◽  
Vol 607 ◽  
pp. 180-182 ◽  
Author(s):  
Radosław Zaleski ◽  
Jacek Goworek
Keyword(s):  
Phase Transitions ◽  
Positron Annihilation ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Irradiation Effects ◽  
Positron Source ◽  
Rigid Rotator ◽  
Positron Annihilation Lifetime ◽  
Silica Wall ◽  
Additional Space ◽  
Mcm 41

The ordering of n-nonadecane confined in the pores of MCM-41 silica was investigated by Positron Annihilation Lifetime Spectroscopy. No irradiation effects caused by the positron source were observed. The ortho-positronium components found in the lifetime spectra correspond to the free volumes observed in the bulk alkane plus additional space at the interface between n-nonadecane and the silica wall. Phase transitions rigid-rotator and rotator-liquid were shifted towards lower temperatures by 28 and 16 degrees respectively.

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