With the global color symmetry model (GCM) at finite chemical potential, the
density dependence of the bag constant, the total energy and the radius of a
nucleon in nuclear matter is investigated. A relation between the nuclear
matter density and the chemical potential with the action of QCD being taken
into account is obtained. A maximal nuclear matter density for the existence of
the bag with three quarks confined within is given. The calculated results
indicate that, before the maximal density is reached, the bag constant and the
total energy of a nucleon decrease, and the radius of a nucleon increases
slowly, with the increasing of the nuclear matter density. As the maximal
nuclear matter density is reached, the mass of the nucleon vanishes and the
radius becomes infinite suddenly. It manifests that a phase transition from
nucleons to quarks takes place.Comment: 18 pages, 3 figure