  New Target-Ion Source Systems combining a target and a catcher material are
developed in the radioactive beam community, in particular at GANIL, in order
to maximise the yield of very short lived atoms by minimizing the atom-to-ion
transformation time. The aim of this study is to characterize the release
properties of 81Rb collected on two graphite catchers and two carbon nanotube
catchers. The release fractions were measured at various catcher-heating
temperatures and then compared to the analytical expressions relevant to each
catcher. This comparison led to the extraction of the pre-exponential factor
(D0) and the activation energy (Eact) involved in the diffusion coefficient of
Rb for three carbon microstructures. All these data allowed to define an ideal
catcher which could be made of aligned carbon nanotubes of small diameter and
oriented in order to collect all the 81Rb atoms produced by the target but also
to release them efficiently.
