What type of nuclear decay release energy but not an particle?

All nuclear decay releases both energy and particles. Even gamma rays from the meta stable decay of Technetium-99m, being only photons, are particles, because a photon is considered a particle - or is it energy? - or is it mass? - hmmm? - see quantum mechanics on that one.

Also, Einsten's famous mass energy equivalence equation e = mc2 states rather plainly that energy is mass and mass is energy. That means that if nuclear decay releases energy, then it also releases mass, and vice versa. There is no way around the equivalence.

Do not misunderstand this. The equation does not mean that energy can be converted into mass or vice versa, it means that energy is mass and vice versa. Neither energy nor mass can be created nor destroyed. So, when an atomic bomb goes off and loses mass generating a high amount of energy, the mass that is lost is simply carried away with the energy.

Sorry if it seems I deviated from the topic, but I did not. This is part of reinforcing the answer and enhancing the explanation.