When two deuterium nuclei are shot at each other they have some probability of fusing into a He nuclei. At the start we have a proton and a neutron in a potential well 1 MeV deep and another proton and neutron in another well 1 MeV deep. At the end we have two protons and two neutrons all in a well 7 MeV deep. At which point a 24 MeV phton can be emitted. My question is what happens in between? Is there a time when the four particles are in a well 2MeV deep, 3MeV, etc. And why don't they radiate lower energy photons as the well forms? Why do they wait until the end to radiate one high energy photon?