Mechanism map for nucleation and growth of helium bubbles in metals

The total free energy of a system containing helium bubbles and point defects (vacancies, helium and self-interstitial atoms) was evaluated and activation barrier for forming a helium bubble was derived, where the effect of helium on helium bubble formation is clearly shown. The rates of inflow to a helium bubble and outflow from a helium bubble were evaluated for vacancies, helium and self-interstitial atoms at the equilibrium and irradiation conditions to understand the mechanism of nucleation and growth of helium bubbles. It indicates that both the thermal emissions of helium and self-interstitial atoms may competitively occur at the irradiation condition from relatively small helium bubbles with high helium pressure.