  Resistively detected nuclear magnetic resonance is used to measure the Knight
shift of the As nuclei and determine the electron spin polarization of the
fractional quantum Hall states of the second Landau level. We show that the 5/2
state is fully polarized within experimental error, thus confirming a
fundamental assumption of the Moore-Read theory. We measure the electron
heating under radio frequency excitation, and show that we are able to detect
NMR at electron temperatures down to 30 mK.
