Joule for Joule radioactivity seems like the only reasonable sense. Who cares if it's one drop of death or a pool full of lightly toxic waste? You could easily

Joule for Joule radioactivity seems like the only reasonable sense. Who cares if it's one drop of death or a pool full of lightly toxic waste? You could easily just dilute the drop to arrive at a similar but less toxic pool (if you wanted to, for some reason).