Nuclear Chemistry 1 Part 05 Nuclear Fission 2

Nuclear Chemistry 1

Part 05 Nuclear Fission 2

1. Nuclear Fission - transformation of large, heavy nucleus into two smaller nuclei - energy and radiation released 3

a. Spontaneous Fission - occurs only rarely - mass number must be greater than 230 4

a. Spontaneous Fission Examples 252 Cf 132 Sn + 117 Cd + 3 98 50 48 100 256 Fm 51 137 Sb + 49 117 In New + 2 0 1 n n n New Liquid Drop Model 5

b. Induced Fission - in the laboratory - neutron bombardment 92 235 U + 0 1 n 56 141 Ba + 3692 Kr + 3 0 1 n 6

b. Categories of Induced Fission 1) Slow neutrons or thermal neutrons (a) can causes neutron capture - isotope is called fertile 92 238 U + 0 1 n 92 239 U fertile slow neutron fissile 7

b. Categories of Induced Fission 1) Slow neutrons or thermal neutrons (b) can cause fission - isotope is called fissile 8

92 235 U + 0 1 n 55 144 Cs + 37 90 Rb +2 0 1 n fissile slow neutron 235 U is the only naturally-occurring isotope that undergoes fission with slow neutrons 9

b. Categories of Induced Fission 2) Fast neutrons - can cause fission - isotope is called fissionable 92 238 U + 0 1 n 57 144 La + 3592 Br + 3 0 1 n 10

b. Induced Fission - products of fission are usually radioactive - start a decay chain that produces more radioactive isotopes and more radiation 11

Example: 92 235 U 39 95 Y 40 95 Zr + 0 1 n 53 138 I + 40 95 Zr + 41 95 Nb + 39 95 Y -1 + 3 0 1 n 0 e -1 0 e 12

2. Discovery of Fission - Fermi and the Joliot-Curies probably discovered fission but didn’t know it! - credit is given to Otto Hahn and Fritz Strassmann in Germany in 1938 - credit was not given to their research partner Lise Meitner - Lise Meitner and her nephew Otto Frisch explained how fission occurs 13

3. Modification of Simple Fission Reaction a. chain reaction - one neutron sets off a series of fissions which produce more neutrons which cause more fissions - need critical mass - minimum mass for fission to occur - amount depends on isotope used - need critical shape - proper geometry for fission to occur - spherical 14

4. Uses of Fission a. Uncontrolled chain reaction - produces an explosion - used to make atomic bombs b. Controlled chain reaction - does not produce explosion - used to make nuclear reactors 15