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Spin Dependent Parton Distributions in a Bound Nucleon

The determination of the spin distribution functions for the neutron requires an understanding of the changes induced by a nuclear medium. We present the first estimates of the changes induced in the spin-dependent, valence parton distributions of the proton and neutron bound in $^3$He and $^6$Li. For $^3$He the result is quite reassuring, in that the off-shell correction to $g_{1n}$ is very small. On the other hand, in $^6$Li the corrections to the spin distributions in the bound proton are sufficiently large that they should be taken into account if one aims for a precision of better than 10%. We provide a simple parametrization of the off-shell changes in the valence spin distributions of $^3$He and $^6$Li, which can be used with any conventional estimate of nuclear binding and Fermi motion corrections.