Well my point is that the energy of the spallation neutrons is monotonically related to the energy of the protons hitting the Tungsten target ... although somewhat lower. I would consider these 100s MeV partiles to be (quite) high energy in contrast to the thermal neutrons alluded to elsewhere. Sure the spallation is lossy, but the result is still pretty high. And the physics is somewhat different with neutron experiments vs. protons... iiuc