  A simple model of particle creation and annihilation in an isolated assembly
of particles with conserved energy and fixed volume, the Cell Model, is
formulated. With increasing time, particle number distribution, obtained by
averaging over many systems, approaches a time-independent, steady state
distribution. Dependence of the steady state distribution on creation and
annihilation conditional reaction probabilities is studied. The results
obtained for the steady state are compared with predictions of statistical
mechanics within the microcanonical ensemble. In general, the predictions of
both models are different. They agree only if the creation and annihilation
conditional probabilities are equal. This condition also results in the
detailed balance in the steady state.
