CORRELATION OF BLISTER DIAMETER AND BLISTER SKIN THICKNESS IN HELIUM-ION-IRRADIATED NB

A systematic study of the correlation between blister diameter and blister skin thickness has been performed for helium-ion irradiation of monocrystalline and polycrystalline Nb for ion energies ranging from 20 to 500 keV. The results indicate that a relationship Dmp∝t1.50 between the most probable blister diameter, Dmp, and blister skin thickness, t, which has been suggested by other authors, does not exist for the various types of Nb targets studied. For example, for room-temperature irradiation of annealed polycrystalline Nb the experimentally determined relationship is D mp=10.3t1.22. Furthermore, the D-t relationship was found to depend on the irradiation temperature in contrast to theoretical predictions by the lateral stress model of blister formation. These results do not appear to support the lateral stress model which predicts the relationship D∝t 1.5. However, the experimentally determined relationships can be explained in part by the gas pressure model of blister formation.