  We investigate the van der Waals interaction between neutrons using the
theory of Casimir and Polder, wherein the potential for asymptotically large
separations falls off as the inverse seventh power, and compare it to the
similar interaction between a neutron and a proton, for which the asymptotic
interaction falls off as the inverse fourth power. Modifications of the
formalism to extend the validity to smaller separations using dynamic electric
and magnetic dipole polarizability data are discussed
