[Pluslucis] 27.April 09: Vortrag Beta-Zerfall und Nukleosynthese

[Helmut Kuehnelt]

EINLADUNG ZUM WIENER PHYSIKALISCHEN KOLLOQUIUM

BETA DECAY AND STELLAR NUCLEOSYNTHESIS
Fritz BOSCH
GSI Helmholtzzentrum für Schwerionenforschung
Darmstadt

Montag, 27. April 2009, 17:30 Uhr
(ab 17:00 Uhr Kaffee)
Universität Wien, Lise Meitner Hörsaal
Strudlhofgasse 4/1. Stock, 1090 Wien


The synthesis of nuclides heavier than iron proceeds in hot stellar 
plasmas by a subtle interplay of beta decay and the capture of neutrons 
or protons. One of the major tasks of nuclear astrophysics is to redraw 
these pathways of stellar nucleosynthesis by providing unstable nuclides 
and by experimentally determining their main properties, the mass and 
the (beta) lifetime. However, in the hot stellar plasmas the nuclides 
are highly ionized which can lead to significant or even dramatic 
changes of beta lifetimes with respect to neutral atoms. The ion 
storage-cooler ring at GSI in Darmstadt, coupled to a synchrotron and a 
fragment separator, is still the only facility where beta decays of 
highly-charged nuclides could be investigated. Four selected examples of 
those experiments will be presented, including their impact for our 
understanding of the s- and r-processes of nucleosynthesis: a) the first 
observation of bound-state beta decay at the example of bare 163Dy: b) 
the dramatic change of the life-time of the "cosmic clock" 187Re when 
all bound electrons are removed; c) the first determination of the ratio 
of bound- and continuum beta decay at the example of bare 207Tl, and d) 
the first measurements of orbital electron capture decays of hydrogen- 
and helium-like nuclides for the examples of 140Pr and 142Pm.