  The properties of low-energy neutron-proton systems are studied in an
effective field theory where only nucleons figure as relevant degrees of
freedom. With a finite momentum cut-off regularization scheme, we show that the
large scattering lengths of the np systems do not spoil the convergence of the
effective field theory, which turns out to be extremely successful in
reproducing, with little cut-off dependence, the deuteron properties, the np
1S0 scattering amplitude and most significantly, the M1 transition amplitude
entering into the radiative np capture process.
