EES 0836 Lecture Notes - Lecture 6: Natural Abundance, Fissile Material, Spontaneous Fission
3 Apr 2016
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Lecture - 6, uranium decay, the natural abundance of uranium today suggests that it was created about 6 billion years ago. Assumes 235u and 238u originally equally abundant. Now have 39. 8% of original 238u and 0. 29% of original 235u. Works out to 0. 72% 235u abundance today: plutonium-239 half-life is too short (24,000 yr) to have any naturally available, thorium-232 is very long-lived, and is a major contributor to geothermal heat. Smacking business: turns out, you would actually loose energy in splitting lighter nuclei, iron is about the most tightly bound of the nuclides. And it"s the release of binding energy that we harvest. So we want to drive toward iron to get the most out: binding energy per nucleon, what does uranium break into? (fish n chips, uranium doesn"t break into two equal pieces. Usually one with mass around 95 a. m. u. and one with mass around 140 a. m. u: the fragments are very neutron-rich, and some drip off immediately.
