We consider the possibility of neutron-antineutron ($n-bar n$) conversion, in which the change of a neutron into an antineutron is mediated by an external source, as can occur in a scattering process. We develop the connections between $n-{bar n}$ conversion and $n-{bar n}$ oscillation, in which a neutron spontaneously tranforms into an antineutron, noting that if $n-{bar n}$ oscillation occurs in a theory with B-L violation, then $n-{bar n}$ conversion can occur also. We show how an experimental limit on $n-{bar n}$ conversion could connect concretely to a limit on $n-{bar n}$ oscillation, and vice versa, using effective field theory techniques and baryon matrix elements computed in the M.I.T. bag model.
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