Topic of neutron skin is very interesting issue related to the asymmetry term in the nuclear
equation of state. The last one is a basis for nuclear physics and e.g. neutron stars. One
of the observables connected with the topic is ratio of number of positive and negative
pions R = N ($π^+$) /N ($π^−$) that can change as a function of Feymann variable $x_F$ . In this
short note we present our study of neutron skin issue by using UrQMD model for ultra
relativistic reactions 208 Pb+ 208 Pb, p + 208 P and $\overline{p}$ + 208 Pb.