In reply to Stephen A. Lawrence's message of Thu, 08 Mar 2007 15:55:17 -0500: Hi, [snip] >Finally, uranium itself may seem to be a puzzle: Where did it come >from? What reaction formed it? The universe started with hydrogen; how >did atoms like uranium "climb the energy hill"? The answer, as I >understand it, is supernova explosions: There is so much energy >released in the explosion, that some amount of it may get "soaked up" >again in the core of the exploding star by _endothermic_ fusion >reactions which do not normally take place.
The standard answer is that even heavy elements like uranium still profit from fusion with a neutron. IOW the mass of the product is less than that of the ingredients. During a supernova explosion, masses of free neutrons are produced, some of which fuse with elements heavier then iron to create even heavier elements. I presume this means that first many neutrons fuse with nuclei till very heavy isotopes are created which then consequently undergo rapid beta decay, and convert into heavier elements before the supply of neutrons runs out (Supernova's don't last very long). Of course some of these heavy elements can be recycled, and end up in new stars, which then get bumped another few levels during the next supernova. Regards, Robin van Spaandonk http://users.bigpond.net.au/rvanspaa/ Competition (capitalism) provides the motivation, Cooperation (communism) provides the means.
