Mixed Ne/Ni beams for radiation damage studies on the harwell variable-energy cyclotron

Ion irradiation facilities which use metal ions beams concurrently with beams of He or He+H have been developed extensively in recent years for the simulation of radiation effects which occur in metals during neutron irradiation in fission or fusion reactors. Helium ions are considered necessary to simulate the effect of helium on cavity nucleation and the metal atom is used to create an adequate atomic displacement rate. Many of these dual-beam facilities require the provision of two accelerators, one to produce a gas atom and the other a metal atom beam, and commonly employ low-energy metal ions (eg. 4 MeV ⁵⁸Ni ⁺) which have a limited range (0.75 μm) in metals of practical interest. Damage can be created at greater depths by use of high energy ions (eg 45 MeV ⁵⁸Ni) in a cyclotron, but charge-to-mass constraints make it difficult to produce a mixed beam of concurrent He and metal ions. It is noted that the heavier inert gas atom neon has similarities in atomistic behaviour in metals to those of helium and could possibly be used as an analogue for helium. In this report we consider this aspect and show than by suitable matching of {e}/{m} ratio a mixed beam of 15 MeV ²⁰Ne ²⁺ and 45 MeV ⁶⁰Ni ⁶⁺ can be obtained from the Harwell VEC with gas/metal atom ratios and beam currents that are suitable for use in radiation damage simulation experiments in metals. It is proposed that exploratory studies should be carried out with mixed Ne/Ni beams into nickel to investigate the possibility of using neon as an analogue for helium in radiation damage simulation studies.