Ahmad Saeedi Graduate Student Department of Physics, Western Illinois University,

1. Nuclear reaction Fission and Fusion Ahmad Saeedi Graduate Student Department of Physics, Western Illinois University, Macomb, IL 61455

2. Outline -History First: Nuclear Fission-Spontaneous Fission -Induced Fission -Process of fission -Chin reaction Second :Nuclear Fusion-Controlling Nuclear Fusion -Conclusion

3. The Discovery of Fission • In 1939, Otto Hahn and Fritz Strassmann announced that uranium nuclei "burst" when they are bombarded with neutrons. - For proving that the barium resulting from his bombardment of uranium with neutrons was the product of nuclear fission, Hahn was awarded the Nobal Prize for Chemistry in 1944 (the sole recipient) "for his discovery of the fission of heavy nuclei"

4. Nuclear reaction A reaction in which an atomic nucleus of a radioactive element splits by bombardment from an external source (like neutrons), with simultaneous release of large amounts of energy, used for electric power generation.

5. First: Nuclear Fission Nuclear fission = nuclear reaction = radioactivity decay   • When atoms are bombarded with neutrons, their nuclei splits into 2 parts which are roughly equal in size. • Nuclear fission in the process whereby a nucleus, with a high mass number, splits into 2 nuclei which have roughly equal smaller mass numbers. • During nuclear fission, neutrons are released

6. 1- Spontaneous Fission • Some radioisotopes contain nuclei which are highly unstable and decay spontaneously by splitting into 2 smaller nuclei. • Such spontaneous decays are accompanied by the release of neutrons.

7. 2- Induced Fission • Nuclear fission can be induced by bombarding atoms with neutrons. • The nuclei of the atoms then split into 2 equal parts. • Induced fission decays are also accompanied by the release of neutrons.

8. The Fission Process • A neutron travels at high speed towards a uranium-235 nucleus. • The neutron strikes the nucleus which then captures the neutron. • The nucleus changes from being uranium-235 to uranium-236. • It then splits into 2 fission fragments and releases neutrons.

9. In a typical example of nuclear fission, one neutron starts the fission of the uranium atom and three more neutrons are produced when the uranium fissions.

10. 235 235 141 96 92 138 U U Cs Kr Ba Rb 2 3 + + + + + + 92 92 55 36 37 56 1 1 1 1 n n n n 0 0 0 0 Examples:

11. Energy from Fission • Both the fission fragments and neutrons travel at high speed. • The kinetic energy of the products of fission are far greater than that of the bombarding neutron and target atom. EK before fission << EK after fission • Energy is being released as a result of the fission reaction.

12. Energy Released • The energy released can be calculated using the equation:

13. + + + 235 138 96 U Cs Rb 2 92 37 55 1 1 n n 0 0 The amount of energy from Fission:

14. + + + 235 138 96 U Rb Cs 2 92 37 55 1 1 n n 0 0 Energy from Fission: Calculate the total mass before and after fission takes place: 235.0439299 + 1.008664916 = 236.0525948 u The total mass after fission (RHS of the equation): 137.911016704 + 95.934272637 + 2(1.008664916) = 235.8626192u

15. The total mass before fission = 236.0529548u The total mass after fission = 235.8626192u Total mass before fission > Total mass after fission

16. Mass difference m= Total mass before fission – Total mass after fission m= LHS - RHS m =236.0525948 – 235.8626192 m = 0.18997565 u • This reduction in mass results in the release of energy.

17. A chain reaction is a self-sustaining reaction. A reaction event stimulates additional reaction events to keep the process going.

18. If a chain reaction occurred in a chunk of pure U-235 the size of a baseball, an enormous explosion would likely result. In a smaller chunk of pure U-235, however, no explosion would occur. • A neutron ejected by a fission event travels a certain average distance before encountering another uranium nucleus. • If the piece of uranium is too small, a neutron is likely to escape through the surface before it “finds” another nucleus. • Fewer than one neutron per fission will be available to trigger more fission, and the chain reaction will die out

19. Second :Nuclear Fusion • Energy is released as light nuclei fuse, or combine, rather than split apart. This process is nuclear fusion. • Energy is released when heavy nuclei split apart in the fission process. • In nuclear fusion, energy is released when light nuclei fuse together. • A proton has more mass by itself than it does inside a helium nucleus.

20. Nuclear Fusion • Atomic nuclei are positively charged. • For fusion to occur, they must collide at very high speeds to overcome electrical repulsion. • Fusion brought about by high temperatures is called thermonuclear fusion.

21. Nuclear Fusion • In the central part of the sun, about 657 million tons of hydrogen are converted into 653 million tons of helium each second. • The missing 4 million tons of mass is discharged as radiant energy.

22. Think! First it was stated that nuclear energy is released when atoms split apart. Now it is stated that nuclear energy is released when atoms combine. Is this a contradiction?

23. Think! First it was stated that nuclear energy is released when atoms split apart. Now it is stated that nuclear energy is released when atoms combine. Is this a contradiction? Answer: This is contradictory only if the same element is said to release energy by both the processes of fission and fusion. Only the fusion of light elements and the fission of heavy elements result in a decrease in nucleon mass and a release of energy.

24. Controlling Nuclear Fusion • In the fusion reactions of hydrogen isotopes, most of the energy released is carried by the lighter-weight particles, protons and neutrons, which fly off at high speeds.

26. Find the Energy released per fusion?

27. Controlling Nuclear Fusion • The development of fusion power has been slow and difficult, already extending over 50 years. • It is one of the biggest scientific and engineering challenges that we face. • Our hope is that it will be achieved and will be a primary energy source for future generations.

28. Difference between Fission and Fusion

29. Conclusion of Nuclear reaction Nuclear fission and nuclear fusion reactions release huge amounts of energy.

30. Acknowledgements: • Dr. S. Mallur physics department, Western Illinois University • www.wikipedia.org • http://www.atomicarchive.com • http://www.diffen.com/difference/Nuclear_Fission_vs_Nuclear_Fusion • Nuclear and Particle Physics, B.R. Martin