  We calculate parity nonconserving observables in the processes where a
neutron is captured on a proton at the threshold energy radiating a photon.
Various potential models such as Paris, Bonn and Argonne $v18$ are used for the
strong interactions, and the meson-exchange description is employed for the
weak interactions between hadrons. The photon polarization $P_\gamma$ in the
unpolarized neutron capture process and photon asymmetry $A_\gamma$ in the
polarized neutron capture process are obtained in terms of the weak
meson-nucleon coupling constants. $A_\gamma$ turns out to be basically
insensitive to the employed strong interaction models and thus can be uniquely
determined in terms of the weak coupling constants, but $P_\gamma$ depends
significantly on the strong interaction models.
