The Target Ion Source
The SPIRAL Target Ion Source production system
In the classic ISOL technique a proton or a light-ion beam is accelerated to a high energy and bombards a thick target producing radioactive nuclei by spallation reactions, fragmentation of the target and/or induced fission. Other reaction mechanisms, however, come into play with heavy ions. In particular, projectile fragmentation is the process of most importance. In all cases, the fragments are stopped in the target which is heated to a high temperature (1800K to 2300K) to facilitate the migration of the radioactive atoms to the surface. Usually the target is located a short distance from the ion source and the radioactive atoms effuse via a transfer tube to the plasma region where they are ionised and then accelerated.
However, given the relatively short range of heavy ions (typically they stop in the production target) one may consider employing very small targets located inside the ion source. Such a configuration would thus eliminate the losses due to sticking of radioactive atoms in the transfer tube - a major source of losses in systems presently in use. As the atoms are ionised and accelerated in a manner identical to that for stable beams, the resulting radioactive beams have good dynamical and optical characteristics when compared with projectile fragmentation, as well as an energy which may be precisely adjusted. The originality of the GANIL project lies in the use of an extended range of heavy-ions produced at high intensities and up to the maximum available energies (e.g. 95 A.MeV, 7.4 eµA for 36Ar18+). Such an approach differs from the proton (or light-ion) beam technique in that the projectile rather than the target is varied in order to produce the different radioactive species.