  We study the motion of topological defects in 1+1 and 2+1 d relativistic
$\phi^6$ model with three equal vacua in the presence of radiation. We show
that even small fluctuations can trigger a chain reaction leading to vanishing
of topological defects. Only one vacuum remains stable and domains containing
other vacua vanish. We explain this phenomenon in terms of radiation pressure
(both positive and negative). We construct an effective model which translates
the fluctuations into additional term in the field theory potential. In case of
two dimensional model we find a relation between the critical size of the bulk
and amplitude of the perturbation.
