Stability of helium-filled platelets in nickel

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Abstract
In order to explain the observed behaviour of helium platelets, which grow and then collapse into clusters of smaller aggregates, a theoretical model is developed to describe the total energy of a platelet. The model is based partly on the results of atomistic computer simulations. The variation of the total energy gives information regarding the platelet stability and is calculated in both a numerical and an analytical way. It is shown that small platelets are stable and that, once a critical radius is attained, the platelet becomes unstable and a transformation into a group of smaller aggregates takes place. The theoretical model can also explain the fact that two-dimensional helium aggregates are observed to be more stable in b.c.c. than in f.c.c. structures.