Speaker
Gilbert GOSSELIN
(Comissariat a l'energie atomique (CEA))
Description
In hot dense plasmas, the electronic environment in the immediate vicinity of the
nucleus is modified, and thus, the plasma conditions influence key processes driving
the lifetime of a nuclear level [1]. A correct lifetime prediction requires every
deexcitation process to be evaluated jointly with its corresponding excitation process.
For heavy nuclei, the nuclear lifetime of discrete levels is often strongly dependent
on internal conversion which involves bound electrons. In plasma, many of these
electrons are no longer in a bound state and the internal conversion rate can be
significantly reduced. Its coupling with its inverse process, Nuclear Excitation by
Electron Capture (NEEC), can lead to greatly increased nuclear lifetimes.
In some cases, an atomic transition can be coupled with a nuclear transition in a
process called Nuclear Excitation by Electron Transition (NEET) if their energies are
closely matched [2]. This can accelerate the deexcitation of the excited nuclear
level, and reduce its lifetime.
We developped a model able to deal with these processes in plasma under thermodynamic
equilibrium. It evaluates internal conversion, NEEC and NEET rates in plasma.
Depending on the particular situation, we use either an average atom description or a
Multi Configuration Dirac Fock (MCDF) approach to describe the electronic environment
of the atom. Large variations of several excited nuclear level lifetimes have been
predicted.
A complete description of the nuclear lifetime must also include some other nuclear
levels through which indirect nuclear excitation or deexcitation may occur. This
particular situation may provide a fast method to populate or depopulate nuclear
isomers [3].
[1] M. R. Harston and J. F. Chemin, Phys. Rev. C59, 2462 (1999)
[2] P. Morel, V. Meot, G. Gosselin, D. Gogny and W. Younes, Phys. Rev. A69, 063414 (2004)
[3] G. Gosselin and P. Morel, Phys. Rev. C70, 064603 (2004)
Author
Gilbert GOSSELIN
(Comissariat a l'energie atomique (CEA))
Co-authors
Dr
Pascal MOREL
(Comissariat a l'energie atomique (CEA))
Dr
Vincent MEOT
(Comissariat a l'energie atomique (CEA))
