  In this article the particle creation process of scalar and spin 1/2
particles in a spatially open cosmological model associated with a universe
filled by radiation and dustlike matter. The Klein-Gordon and Dirac equations
are solved via separation of variables. After comparing the{\it \ in }and% {\it
\ out} vacua, we obtain that the number of created particles corresponds to
  Planckian and Fermi-Dirac distributions for the scalar and Dirac cases
