  Vaporized and multifragmenting sources produced in heavy ion collisions at
intermediate energies are good candidates to investigate the phase diagram of
nuclear matter. The properties of highly excited nuclear sources which undergo
a simultaneous disassembly into particles are found to sign the presence of a
gas phase. For heavy nuclear sources produced in the Fermi energy domain, which
undergo a simultaneous disassembly into particles and fragments, a fossil
signal (fragment size correlations) reveals the origin of
multifragmentation:spinodal instabilities which develop in the unstable
coexistence region of the phase diagram of nuclear matter. Studies of
fluctuations give a direct signature of a first order phase transition through
measurements of a negative microcanonical heat capacity.
