What type of nuclear decay releases energy but not a particles?
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