Lect14 -- Nuclear Principles

0055 246 kyr 235u 0720 704 myr 236u 0 23 myr 237u 0 68

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Unformatted text preview: r other energetic particle), but not when hit by slow neutrons – so not practical for reactors Uranium and related isotopes Isotope Abundance (%) half-life decays by: 233U 0 159 kyr α 234U 0.0055 246 kyr α 235U 0.720 704 Myr α 236U 0 23 Myr α 237U 0 6.8 days β- 238U 99.2745 4.47 Gyr α 239Pu no natural Pu 24 kyr α 232Th 100 14 Gyr α Why fission of 235U but not 238U? Bottom line: at thermal energies (arrow), 235U is 1000 times more likely to undergo fission than 238U even when smacked hard The fission cheat sheet 235U will undergo spontaneous fission if a neutron happens by, resulting in: •  two sizable nuclear fragments flying out •  a few extra neutrons •  other energetic particles released The net result: lots of banging around generates heat locally (kinetic energy of tiny particles) For every gram of 235U, get 65 trillion Joules, or about 16 million Calories… compare to gasoline at roughly 10 Calories per gram means a tank of gas could be replaced by a 1-mm pellet o...
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