I present in this talk the latest results of the neutron spin physics program at Jefferson Laboratory in Hall A using the highly polarized electron beam and a high pressure polarized ³He target. This program includes among others experiment E99-117 in which the neutron spin asymmetry <IMG SRC="/img/revistas/bjp/v34n3a/a74img01.gif">was measured in the deep inelastic region with high precision. This asymmetry is observed, for the first time, to change sign from negative to positive values between 0.3 < x < 0.6. Furthermore we perform a flavor decomposition of the spin-dependent to spin-independent quark distributions ratios in the nucleon and find that relativistic quark models are in better agreement than pQCD fits using the hadron helicity conservation constraint as x -> 1.
