The effect of low‐temperature (liquid nitrogen) reactor irradiation on the white‐to‐grey tin transformation has been investigated. It was found that, compared to an unirradiated pure sample, the transformation, measured by dilatometry, is drastically accelerated by prior irradiation. The irradiation apparently eliminates the normally very long induction period. The kinetic behavior of reactor irradiated samples and of samples seeded with grey tin were found to be qualitatively similar. These results indicate that the defects introduced into white tin by reactor irradiation serve as nuclei, or at least embryos of nucleation, for the subsequent phase transformation. Whether point defects, their aggregates, or the strains surrounding the displaced atoms are responsible for the artificial ``seeding'' cannot yet be decided. Reactor irradiation appears to be a promising new tool for studying nucleation and growth processes since quite uniform artificial nucleation can be accomplished this way.