<Dl> <Dd> 235 92 U → 7.038 × 10 8 y α 231 90 Th → 25.52 h β − 231 91 Pa → 3.276 × 10 4 y α 227 89 Ac (→ 21.773 y 98.62% β − 227 90 Th → 18.718 d α → 21.773 y 1.38% α 223 87 Fr → 21.8 min β −) 223 88 Ra → 11, 434 d α 219 86 Rn 219 86 Rn → 3.96 s α 215 84 Po → 1.778 ms α 211 82 Pb → 36.1 min β − 211 83 Bi (→ 2, 13 min 99.73% α 207 81 Tl → 4, 77 min β − → 2, 13 min 0, 27% β − 211 84 Po → 0, 516 s α) 207 82 Pb (stable) (\ displaystyle (\ begin (array) (l) (\ ce (^ (235) _ (92) U -> (\ alpha) (7.038 \ times 10 ^ (8) \ (\ ce (y))) _ (90) ^ (231) Th -> (\ beta ^ (-)) (25.52 \ (\ ce (h))) _ (91) ^ (231) Pa -> (\ alpha) (3.276 \ times 10 ^ (4) \ (\ ce (y))) _ (89) ^ (227) Ac)) (\ begin (Bmatrix) (\ ce (-> (98.62 \% \ beta ^ (-)) (21.773 \ (\ ce (y))) _ (90) ^ (227) Th -> (\ alpha) (18.718 \ (\ ce (d))))) \ \ (\ ce (-> (1.38 \% \ alpha) (21.773 \ y) _ (87) ^ (223) Fr -> (\ beta ^ (-)) (21.8 \ (\ ce (min))))) \ end (Bmatrix)) (\ ce (^ (223) _ (88) Ra -> (\ alpha) (11,434 \ (\ ce (d))) _ (86) ^ (219) Rn)) \ \ (\ ce (^ (219) _ (86) Rn -> (\ alpha) (3.96 \ (\ ce (s))) _ (84) ^ (215) Po -> (\ alpha) (1.778 \ (\ ce (ms))) _ (82) ^ (211) Pb -> (\ beta ^ (-)) (36.1 \ (\ ce (min))) _ (83) ^ (211) Bi)) (\ begin (Bmatrix) (\ ce (-> (99.73 \% \ alpha) (2, 13 \ (\ ce (min))) _ (81) ^ (207) Tl -> (\ beta ^ (-)) (4, 77 \ (\ ce (min))))) \ \ (\ ce (-> (0, 27 \% \ beta ^ (-)) (2, 13 \ (\ ce (min))) _ (84) ^ (211) Po -> (\ alpha) (0,516 \ (\ ce (s))))) \ end (Bmatrix)) (\ ce (^ (207) _ (82) Pb_ ((stable)))) \ end (array))) </Dd> </Dl> <Dd> 235 92 U → 7.038 × 10 8 y α 231 90 Th → 25.52 h β − 231 91 Pa → 3.276 × 10 4 y α 227 89 Ac (→ 21.773 y 98.62% β − 227 90 Th → 18.718 d α → 21.773 y 1.38% α 223 87 Fr → 21.8 min β −) 223 88 Ra → 11, 434 d α 219 86 Rn 219 86 Rn → 3.96 s α 215 84 Po → 1.778 ms α 211 82 Pb → 36.1 min β − 211 83 Bi (→ 2, 13 min 99.73% α 207 81 Tl → 4, 77 min β − → 2, 13 min 0, 27% β − 211 84 Po → 0, 516 s α) 207 82 Pb (stable) (\ displaystyle (\ begin (array) (l) (\ ce (^ (235) _ (92) U -> (\ alpha) (7.038 \ times 10 ^ (8) \ (\ ce (y))) _ (90) ^ (231) Th -> (\ beta ^ (-)) (25.52 \ (\ ce (h))) _ (91) ^ (231) Pa -> (\ alpha) (3.276 \ times 10 ^ (4) \ (\ ce (y))) _ (89) ^ (227) Ac)) (\ begin (Bmatrix) (\ ce (-> (98.62 \% \ beta ^ (-)) (21.773 \ (\ ce (y))) _ (90) ^ (227) Th -> (\ alpha) (18.718 \ (\ ce (d))))) \ \ (\ ce (-> (1.38 \% \ alpha) (21.773 \ y) _ (87) ^ (223) Fr -> (\ beta ^ (-)) (21.8 \ (\ ce (min))))) \ end (Bmatrix)) (\ ce (^ (223) _ (88) Ra -> (\ alpha) (11,434 \ (\ ce (d))) _ (86) ^ (219) Rn)) \ \ (\ ce (^ (219) _ (86) Rn -> (\ alpha) (3.96 \ (\ ce (s))) _ (84) ^ (215) Po -> (\ alpha) (1.778 \ (\ ce (ms))) _ (82) ^ (211) Pb -> (\ beta ^ (-)) (36.1 \ (\ ce (min))) _ (83) ^ (211) Bi)) (\ begin (Bmatrix) (\ ce (-> (99.73 \% \ alpha) (2, 13 \ (\ ce (min))) _ (81) ^ (207) Tl -> (\ beta ^ (-)) (4, 77 \ (\ ce (min))))) \ \ (\ ce (-> (0, 27 \% \ beta ^ (-)) (2, 13 \ (\ ce (min))) _ (84) ^ (211) Po -> (\ alpha) (0,516 \ (\ ce (s))))) \ end (Bmatrix)) (\ ce (^ (207) _ (82) Pb_ ((stable)))) \ end (array))) </Dd> <P> The fission of one atom of uranium - 235 generates 202.5 MeV = 3.24 × 10 J, which translates to 19.54 TJ / mol, or 83.14 TJ / kg . This is around 2.5 million times more than the energy released from burning coal . When 235 92 U nuclides are bombarded with neutrons, one of the many fission reactions that it can undergo is the following (shown visually in the adjacent image): </P> <P> Heavy water reactors, and some graphite moderated reactors can use unenriched uranium, but light water reactors must use low enriched uranium because of light water's neutron absorption . Uranium enrichment removes some of the uranium - 238 and increases the proportion of uranium - 235 . Highly enriched uranium (HEU), which contains an even greater proportion of uranium - 235, is sometimes used in nuclear weapon design . </P>

The fission of 235u (uranium - 235) nuclei is initiated by
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