  Around the nuclear Fermi momentum, there is a transition of nucleon momentum
distribution n(k) in nuclear matter, i.e., from a constant to the $1/k^{4}$
nucleon momentum distribution. While nowadays the transition momentum of
minority in asymmetric matter is rarely studied and thus undetermined. In the
framework of the IBUU transport model, proton transition momentum in nuclei is
first studied. It is found that the transition momentum of proton is sensitive
to the $\pi^{-}/\pi^{+}$ ratio as well as the energetic photon production in
neutron-rich nuclear reaction. This result may push the study of how the proton
momentum is distributed in neutron-rich matter forward and help us to better
understand the dynamics of both neutron-rich nuclear reactions and neutron
stars.
