ELFT HÍRADÓ

["Dr. KAJCSOS, Zsolt" <kajcsos AT rmki.kfki.hu>]

CMRC SZEMINÁRIUM

Prof. Morten Eldrup

Riso/Denmark


"Detection and characterisation of defects in metals and molecular solids
by positron and positronium trapping"

Positron Annihilation Spectroscopy (PAS) may be used to detect and 
characterize vacancy-type

defects and free volume regions in metals and alloys as well as in 
molecular solids. The

reason for this is that in metals and alloys, injected positrons are 
attracted to and may

become trapped at vacancies and vacancy-type defects (such as voids, 
gas-bubbles,

dislocations etc.). The annihilation characteristics of the positrons 
(positron lifetime and

positron-electron momentum distribution in particular, which can be 
detected by nuclear

spectroscopy methods) depend on the type of defect in which the positrons 
are trapped.
In most molecular solids some of the injected positrons form a bound 
positron-electron state

called positronium (Ps). In such solids, Ps will become trapped in open 
volume regions such

as vacancies in crystals and free volume in polymeric materials, and like 
in metals the

annihilation characteristics will depend on the trapping site.
In the talk a number of examples of defect studies with PAS will be 
discussed, which will

illustrate the sensitivity of the technique to both defect density and size 
and emphasize

the usefulness of PAS in investigations of sub-nanometer sized defects and 
open volumes.






2003. október 27-én, hétfon 14 órakor
az RMKI Tanácsteremben (III. ép. II. em.)



> 1121 Budapest, Konkoly-Thege u. 29-33.
> Szervezi: Kajcsos Zsolt, KFKI RMKI, 
> kajcsos AT rmki.kfki.hu