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 3He and 6Li. For 3He the result is quite reassuring, in that the off-shell correction to g1n is very small. On the other hand, in 6Li 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 3He and 6Li, which can be used with any conventional estimate of nuclear binding and Fermi motion corrections.