For my level of understanding the only explanation of mass to energy, ie nuclear weaponry, is limited to a simple summing game where a mass deficit is expressed as energy. For the 'reverse' process, ie in the LHC at CERN, it is a similar story, energy in, mass out.
Is there a more detailed physical explanation of what is occuring and if so is it mirrored by the two processes?
(Obviously pure physical theory at some level is just numbers in, numbers out but that alone doesn't preclude the possibility of some physical description between high level text book and base theory.)