  A precise measurement of the neutron decay $\beta$-asymmetry $A_0$ has been
carried out using polarized ultracold neutrons (UCN) from the pulsed spallation
UCN source at the Los Alamos Neutron Science Center (LANSCE). Combining data
obtained in 2008 and 2009, we report $A_0 = -0.11966 \pm
0.00089_{-0.00140}^{+0.00123}$, from which we determine the ratio of the
axial-vector to vector weak coupling of the nucleon $g_A/g_V =
-1.27590_{-0.00445}^{+0.00409}$.
