Pardon me, I reread David's previous post
David said:
"What is needed to do it right is Curium, not Uranium nor Plutonium."
David did read the link (I am the guy being stupid). My apologies.
There are some isotopes of americium or californium that have amazing fission cross sections. In theory one could make a fission bomb that could fit in a pack of cigarettes. Fortunately these isotopes are very hard to make and too expensive for military use.
Gary
