Q: An explosion of atomic bomb release an energy of 7.6 × 1013 J. If 200 MeV energy is released on fission of one U235 atom calculate :
(i) the number of uranium atoms undergoing fission.
(ii) the mass of uranium used in the atom bomb.
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Sol: E = 7.6 × 103 J; Energy released per fission = 200 MeV
= 200 × 106 × 1.6 × 10-19 = 3.2 × 10-11 J
Number of uranium atoms (n) = (Total energy)/(Energy per fission)
n = (7.6 × 1013)/(3.2 × 10-11 ) = 2.375 × 1024 atoms
Avogadro number (N) = 6.023 × 1023 atoms
Mass of uranium = (n × 235)/N = (2.375 × 1024 × 235 )/(6.023 × 1023 ) = 92.66 g.