There has been much research into the recently discovered iron based superconductors, but so far only the magnetic excitations at low energy have been investigated. We propose to study the spin fluctuations in the optimally doped superconductor BaFe1.9Ni0.1As2 up to around 150 meV. We will study the dispersion and spectral weight at high energies and compare with previous data collected on iron arsenide parent compounds.