  Contributions of perturbative pions around a non-trivial fixed point are
studied by utilizing di-baryon fields. We calculate ${}^1S_0$ and ${}^3S_1$
phase shifts for the $np$ scattering at low energies up to one-pion-exchange
contributions. We also calculate effective range parameters, $v_2$, $v_3$ and
$v_4$ in the higher order of the effective range expansion, and obtain
corrections of the effective range to the expressions previously reported by
Cohen and Hansen. After the scattering length and the effective range are
renormalized, we study the role of renormailzation scale parameter $\mu$ and
discuss the range of validity of the theory.
