Let's say I'm a transdimensional or quasi-divine being whose pastime is acting as the patron for some mortal sorcerer who would very much like to turn lead into gold to impress their fellow corporeal beings. Being that I am benevolent and good and do not want my mortal playthings... i mean friends to be turned into radioactive dust, how might I turn all this energy into something less harmful, without violating the principle of conservation of energy as a whole?
(Specifically, I'm looking for a form of energy or matter that could be used to "store" the other deadly energy that a magic user might produce if they tried to transmute a heavier element into a lighter one. The presence of the transdimensional being is there to explain how all this is able to happen - they possess superior knowledge of physics and thus are aware of the dangers which they work to circumvent because they want to. For the purposes of this question they are constrained by the first law of thermodynamics, although they're obviously able to manipulate other laws of nature for this to even be a question.)