When a nuclear reaction occurs in only even-even nuclei, the nuclear reaction is a result of photo fission.
Remember, Rossi states at his reaction is centered on the Ni62 and Ni64 nickel isotopes. DGT states that all even isotopes of nickel react but Ni61 does not. This is a possible indication that a low spin nuclear reaction based on photo fission is occurring. https://user.physics.unc.edu/research/nuclear/photonuclear_phys/photofission.php “The absorption of a photon by a heavy, even-even causes an excitation to an unstable, low-spin state. The states will subsequently undergo a nuclear reaction or decay to reach a more stable configuration. One likely reaction available to heavy nuclei is fission, the splitting of the original nucleus into two distinct nuclei, also known as fragments. Fission occurs when the nuclear shape deforms to the point when the Coulomb repulsion overcomes the nuclear surface tension; the nucleus is then unbound and splits into two nuclei, referred to as fragments.”
