  We study the nonmesonic weak decay (NMWD) $\Lambda N \to nN$ of the
${}^{12}_{\Lambda} C$ hypernucleus induced by the nucleon $N=n,p$ with
transition rate $\Gamma_N$. The nuclear process is described by the interplay
of two models; one describing the NMWD of hyperon $\Lambda$ in the nuclear
environment, and the other taking into account the Final State Interaction
(FSI) of the two outgoing nucleons with the residual nucleus. The first one is
done in the framework of the Independent-Particle Shell-Model (IPSM), with the
decay dynamics represented by the exchange of $\pi+ \eta+ K+\rho+\omega+K^*$
mesons with usual parametrization. For the second one is used a time dependent
multicollisional intranuclear cascade schema (implemented in the CRISP code -
Collaboration Rio-S\~ao Paulo). The results obtained for inclusive and
exclusive kinetic energy spectra, and the angular correlation are compared with
recent data from KEK and FINUDA experiments. The calculated ratio $(\Gamma_n /
\Gamma_p)^{\partial{\tiny FSI}}$, between the numbers of emitted back-to-back
$nn$ and $np$ pairs, is in good agreement with the experimental data.
