Probably going to get lots of downvotes for that name... Anyway, assume that you have a zeppelin, made entirely out of lead. What gas would be required to hold this in the air? Would this contraption even be able to stay together, or would it fall apart in the air?
Assumptions–The gas in the zeppelin does not have to be naturally occuring, or radioactively stable. It just needs to have a very low density. The zeppelin is approximately the size of modern-day zeppelins, or, seeing as those aren't too common, 200,000 $m^3$. The envelope is the only thing made of lead. This is also at standard temperature(think between 60 ºF and 90ºF, 1 atm pressure, earth gravity.