...Activating stable iodine isn't how we make I-131. There's some very short half life steps on the order of minutes in the there that send the party off in radioxenon territory. We normally make I-131 by activating stable Te-130 when we want to do it on purpose. Like Sr-90 and Cs-137, all the radioiodines but particularly I-131 are fission products. The creation of radioactive P-32 from stable P-31 is pretty straightforward single neutron absorption activation. P-32 is also a very common isotope used in research that people will recognize. You could do the creation of tritium, H-3, from deuterium, H-2, but that asking people to recognize there's more than one kind of hydrogen in the world for their water.