[SOLVED] photon+deuteron-->p+n , E(photon)=? Problem: What is the minimal energy of photon for disassembling deuteron on proton and neutron (photon+d --> p+n)? By how much is that energy larger than energy of binding of deuteron? Binding energy of deuteron is E=2.225MeV, mass of deuteron is 1875.628MeV. This means that m(d)-m(p)-m(n)=2.225MeV. I don't understand why would do you need a photon of greater energy than 2.225MeV if that is the energy that binds proton and neutron together.