SURFACE BLISTERING OF MOLYBDENUM IRRADIATED WITH 75-350-KEV HELIUM IONS

Polycrystalline molybedenum samples have been irradiated at room temperature with helium ions of energy from 75 to 350 keV in high vacuum. Irradiation parameters such as ion energy, total dose, and dose rate were varied and surfaces were examined in a scanning electron microscope. The average blister diameter increases with increasing ion energy and the blister number density increases with increasing total dose of helium. The critical dose for blister formation is independent of the beam flux in the range of 6. 7 multiplied by 10**1**3 to 2 multiplied by 10**1**5 ions cm** minus **2 s** minus **1. However, the average blister diameter changes with the change of flux. When the molybdenum surface is successively bombarded with varying ion energies, both the diameter and the number density of the blisters is significantly reduced as compared to monoenergetic helium bombardment.