I think adding the principle of isotopes would be a good idea: for example, a material subjected to strong neutron radiation emits a weak one in the next minute, that water absorbing a neutron has a low chance of to become deuterium oxide, or that the uranium subjected to radiation becomes fissile (U239-> U235) ... It would then be necessary to add an "irradiated state" to the particles (0 = ordinary element 1 = stable isotope 2 = radioactive isotope 3 = fissile isotope ...). What do you think about this idea ?

this would allow fissile uranium nuclear power plants, several means of obtaining deuterium, radioactive gases (tritium with hydrogen), nuclear fallout ...