Simulation for optimization the dimension of the Ir And Re surface ion source at ALTO Project

In order to study the nuclear structure of the neutron-rich germanium isotopes at ALTO (Accelerateur lineaire aupres de Tandem d'Orsay) via the β---decay of the neutron-rich gallium mother isotopes, it is necessary to be able to produce a highly intense and pure gallium beam. To obtain such a beam, we use the ISOL (Isotope-separation online) technique for fissioning 238U in a thick UCx target. In this approach, the ion source plays a key role and for gallium isotopes the positive surface ion source is a good candidate because the ionization potential of the neighboring elements is sufficiently higher than its own one. Hence, for our case, the surface ion source can provide us with high selectivity. The higher efficiency will be obtained when refractory metals with a high work function are chosen as ionizer cavity. For a surface ion source made by a given metal, in order to get highest ionization efficiency, the simulation for optimization the dimension of the ionization tube made from a given material is very important. In this report, the basic theory of the surface ion source and simulation method as well as its results for surface ion source using Ir and Re are shown. (author)