  In this paper we study the creation of super-massive real scalar particles in
the framework of a $f(R)=R-\beta/R^n$ modified gravity theory, with parameters
constrained by observational data. The analysis is restrict to a homogeneous
and isotropic flat and radiation dominated universe. We compare the results to
the standard Einstein gravity with cosmological constant ($\Lambda CDM$ model),
and we show that the total number density of created particles in the $f(R)$
model is very close to the standard case. Another interesting result is that
the spectrum of created particles is $\beta$ independent at early times.
