I thought spallation was only caused by impact of momentous particles. (That is, not including photons.) You knock a nucleus on the front, and, Newton’s Cradle style, a neutron pops out the back. (Which in any case is different from star formation which completely blows the nucleus apart. )
Photons can do it too. With photoneutrons, you get neutrons, with spallation by photons you can get bigger particles. Takes an energetic photon.