Is there a way to compute or explain if a decay prefers decaying into mainly mass or mainly energy ? I know quarks prefer to decay into the most massfull quarks : http://hyperphysics.phy-astr.gsu.edu/hbase/particles/qrkdec.html
And emitting photons is a (or partially is) a massless decay.
I only know E = gamma mc^2 from relativity must hold and the things must be expressable in quanta (so no irrational energy/mass ratio or such).
Plz not all complicated answers , im no expert in QM.