[en] We report on measurements of the neutron spin asymmetries A_1,2ⁿ and polarized structure functions g_1,2ⁿ at three kinematics in the deep inelastic region, with x = 0.33, 0.47 and .60 and Q₂ = 2.7, 3.5 and 4.8 (GeV/c)², respectively. These measurements were performed using a 5.7 GeV longitudinally-polarized electron beam and a polarized ³He target. The results for A₁ⁿ and g₁ⁿ at x = 0.33 are consistent with previous world data and, at the two higher x points, have improved the precision of the world data by about an order of magnitude. The new A₁ⁿ data show a zero crossing around x = 0.47 and the value at x = 0.60 is significantly positive. These results agree with a next-to-leading order QCD analysis of previous world data. The trend of data at high x agrees with constituent quark model predictions but disagrees with that from leading-order perturbative QCD (pQCD) assuming hadron helicity conservation. Results for A₂ⁿ and g₂ⁿ have a precision comparable to the best world data in this kinematic region. Combined with previous world data, the moment d₂ⁿ was evaluated and the new result has improved the precision of this quantity by about a factor of two. When combined with the world proton data, polarized quark distribution functions were extracted from the new g₁ⁿ/F₁ⁿ values based on the quark parton model. While results for Δu/u agree well with predictions from various models, results for Δd/d disagree with the leading-order pQCD prediction when hadron helicity conservation is imposed