  In this work, a model for the n p --> d (pi pi) reaction is developed. It is
shown that the structure of the deuteron momentum spectra for a neutron beam
momentum of 1.46 GeV can be explained as a consequence of the interplay of two
mechanisms involving the excitation of the N^*(1440) resonance and its
subsequent decay into N (pi pi)^{T=0}_{S-wave} and Delta pi respectively. The
relevance of the present analysis for the study of the Roper excitation and
decay properties, as well as for the interpretation of other two-pion
production experiments is discussed.
