  The reactions of nucleon and polarized deuteron scattered off a heavy target
at large impact parameter with intermediate energies have been investigated by
using the improved quantum molecular dynamics model. It is found that, due to
the difference effect of isovector potential on proton and neutron, there is a
significant difference between the angle distribution of elastic scattering
protons and neutrons. To overcome the lack of monochromatic neutron beam, the
reaction of polarized deuteron peripherally scattered off the heavy target is
used to replace the reaction of individual proton and neutron scattered off
heavy target to study the isospin effect. It is found that the distributions of
elastic scattering angle of proton and neutron originating from the breakup of
deuteron are very similar to the results of the individual proton- and
neutron-induced reaction. A new probe more effective and more clean, namely the
difference between elastic scattering angle of proton and neutron originating
from the breakup of polarized deuteron, is promoted to constrain the symmetry
energy at subsaturation density.
