  It is shown that quantum nucleardynamics (QND) as an SU(2)_N \times U(1)_Z
gauge theory, which is generated from quantum chromodynamics (QCD) as an
SU(3)_C gauge theory through dynamical spontaneous symmetry breaking,
successfully describes nuclear phenomena at low energies. The proton and
neutron assigned as a strong isospin doublet are identified as a colorspin plus
weak isospin doublet. Massive gluon mediates strong interactions with the
effective coupling constant G_R/\sqrt{2}= g_n^2/8 M_G^2 \approx 10 GeV^{-2}
just like Fermi weak constant G_F/\sqrt{2} = g_w^2/8 M_W^2 \approx 10^{-5}
GeV^{-2} in the Glashow-Weinberg-Salam model where g_n and g_w are the coupling
constants and M_G and M_W are the gauge boson masses. Explicit evidences such
as lifetimes and cross sections of nuclear scattering and reaction, nuclear
matter and charge densities, nucleon-nucleon scattering, magnetic dipole
moment, gamma decay, etc. are shown in support of QND. The baryon number
conservation is the consequence of the U(1)_Z gauge theory and the proton
number conservation is the consequence of the U(1)_f gauge theory.
