Comprehensive and high-accuracy n→-He3 elastic scattering analyzing power Ay(θ) angular distributions were obtained at five incident neutron energies between 1.60 and 5.54 MeV. The data are compared to rigorous four-nucleon calculations using high-precision nucleon-nucleon potential models; three-nucleon force effects are found to be very small. The agreement between data and calculations is fair at the lower energies and becomes less satisfactory with increasing neutron energy. Comparison to p-He3 scattering over the same energy range exhibits unexpectedly large isospin effects.DOI: http://dx.doi.org/10.1103/PhysRevLett.110.152503Received 8 December 2012Published 12 April 2013© 2013 American Physical SocietyArticle Available via CHORUSDownload Accepted Manuscript