  We study the creation of high energy SM particles in the Starobinsky model of
dark energy (a variant of F(R)-gravity) inside the regions contracting due to
the Jeans instability. In this modification of gravity the additional degree of
freedom -- scalaron -- behaves as a particle with mass depending on matter
density. So when the mass changes light scalarons could be created at a
non-adiabatic stage. Later scalaron mass grows and could reach large values,
even the value of 10^{13} GeV, favored by early-time inflation. Heavy scalarons
decay contributing to the cosmic ray flux. We analytically calculated the
number density of created particles for the case of exponential (Jeans)
contraction and found it negligibly small provided the phenomenologically
viable and cosmologically interesting range of model parameters. We expect
similar results for a generic model of F(R)-gravity mimicking cosmological
constant.
