Neutron spin-dependent structure function, Bjorken sum rule, and first evidence for singlet contribution at low x

We perform the isospin decomposition of proton and neutron SLAC data in the region $0.01 \leq x \leq 0.1$. The isovector part is well described by a power behaviour $x^{\alpha}$, where $\alpha$ leads to the validity of Bjorken sum rule and it is consistent with the power extracted from all previous data using NLO evolution. The isoscalar part behaviour may be interpreted as a partial cancellation between a positive non-singlet contribution and a singlet one strongly negative.