Dual-beam, charged-particle irradiation facility for simulation of nuclear environment

Heavy-ion bombardment provides a method for simulating neutron damage to metals and other materials. Simultaneous implantation of He+ ions allows the study of effects of neutronically generated helium in these samples. A 2-MeV Van de Graaff and a 2-MeV tandem accelerator at Battelle, Pacific Northwest Laboratories (PNL) have been combined to provide dual-beam irradiation with heavy ions, Ni++ or Ta++, and with He+ ions. This irradiation facility allows independent control of beam currents and energies for both heavy-ion and helium-ion beams, as well as sample temperatures to 12000C. It will be used both for investigation of materials for advanced reactor applications and for basic studies of radiation damage mechanisms. Preliminary results on molybdenum irradiated to two dose levels at 10000C, with and without simultaneous helium implantation, show the effect of helium on void nucleation. When helium is continuously implanted, the number of voids increases with dose. Without helium, existing voids grow in size but the number is unchanged. At higher heavy-ion dose rates, this effect of helium is less pronounced