All this talk about Nuclear chain reaction reminds me of the true story about David Hahn, the Radioactive Boy Scout.
If you've never read the story it's definitely worth the short read:-
http://www.abc.net.au/science/articl...e&topic=latest
To start with David built himself a neutron gun from Americium-241 he found in Smoke Detectors. But alas, it didn't produce enough neutrons to start the reaction....so he went for plan B.
I won't spoil the rest of the story for you, but every time I read it it brings a smile to my face. (But not in an evil Dr No type way, more like that makes my carrot top experiment look lame.)
"Where's my shed gone, son?" I can only imagine the look on his parents face.
Now...bringing it back to Astronomy Science, I'm struggling to work out what is happening on Jupiter. It's a gaseous planet, approximately 90% hydrogen, but produces more radioactivity than any other planet in the solar system. How can that be?
As I understand it the Pioneer Probes discovered the amazing amount of radioactivity, and the Voyager Probes had to be reconfigured/redesigned to take it into account.