Correlation between blister skin thickness, the maximum in the damage-energy distribution, and projected ranges of helium ions in Nb for the energy range 10-1500 keV

The skin thickness of blisters formed on polycrystalline niobium under irradiation at room temperature by ⁴He ⁺ at energies of 15 to 80 keV have been measured. Similar measurements were conducted for 10-keV ⁴He ⁺ irradiation at 500°C to increase blister exfoliation, and thereby allow examination of a larger number of blister skins. For energies less than 100 keV the skin thicknesses are compared with both the projected range and the damage-energy distributions constructed from moments interpolated from Winterbon's tabulated values. The projected ranges and damage-energy distributions have also been computed with a Monte-Carlo program. For energies greater than 100 keV the projected ranges of ⁴He ⁺in Nb were calculated using either Brice's formalism or the one given by Schiøtt. The thicknesses of blister skins for 60 and 80-keV irradiations, and those reported earlier for 100 to 1500-keV irradiations correlate well with calculated projected ranges. For irradiation energies less than 60 keV the measured thicknesses are greater than the calculated ranges.