Initial state effects in deep inelastic neutron scattering.

We develop a new approach to the impulse aproximation which was first used by Gunn et al [1]. We assume, as is consistent with the existence of a single particle momentum distribution, that the struck atom has initial and final state single particle wavefunctions ψi.(r) and ψf(r) respectively. This is clearly valid when the environment of the atom can be approximated by a single particle potential [2] as for example in the Born-Oppenheimer approximation and can also be formally justified in the impulse limit for a many body system such as He4.