1. Nuclear Reactions Contents: Nuclear reactions Whiteboard Hahn and Strassmann and nuclear fissionHahn and Strassmann and nuclear fission Einstein’s Letter to Roosevelt The Manhattan Project Hiroshima and Nagasaki Fusion reactions Nuclear Power

2. Nuclear reactions TOC Charge and nucleon number are conserved Can be written as follows: 4 2 He + 14 7 N ---> 17 8 O + 1 1 H 14 7 N( , p) 17 8 O Initial Nucleus( bombarding particle,emitted particle )Final Nucleus  = 4 2 He, p = 1 1 H, d (deuterium) = 2 1 H, t (tritium) = 3 1 H, 1 0 n = neutron, 0 0  = gamma Left side mass vs right side mass Exoergic - releases energy Endoergic - requires energy Particle accelerators provide energy for endoergic

3. Nuclear reactions - example TOC What’s the initial nucleus? ??? + n ---> p + 14 6 C ??? (n, p) 14 6 C ? ? XX + 1 0 n ---> 1 1 p + 14 6 C 14 7 N

4. Whiteboards: Nuclear Reactions 11 | 2 | 3 | 4234 TOC

5. W 137 56 Ba(n,  ) ??? (hint) 138 56 Ba 0 0  137 56 Ba + 1 0 n ---> 0 0  + ? ? XX 138 56 Ba

6. W 137 56 Ba(n, ?) 137 55 Cs p 137 56 Ba + 1 0 n ---> ? ? XX + 137 55 Cs 11p11p

7. W 2 1 H(d, ?) 4 2 He (1 hint)  21d21d 2 1 H + 2 1 H ---> ? ? XX + 4 2 He 0000

8. W 197 79 Au( , d) ??? (2 hints) 199 80 Hg 4242 2 1 d 197 79 Au + 4 2  ---> 2 1 d + ? ? XX 199 80 Hg

9. W 9 4 Be(?, t) 8 4 Be (1 hint) 21d21d 3 1 t 9 4 Be + ? ? XX ---> 3 1 t + 8 4 Be 21d21d

10. W Is this reaction exoergic or endoergic? What energy does it require or give off? 197 79 Au( , d) 199 80 Hg 197 79 Au =196.966543  = He = 4.002602 total = 200.969145 199 80 Hg =198.968253 d = 2 H = 2.014102 total = 200.982355 It gains 0.01321 u of mass, so it requires (0.01321)(931.5) = 12.31 MeV of energy This is endoergic

11. W exo.53 MeV Try this reaction - is it endo or exo, and how much? 40 19 K(p, n) 40 20 Ca 40 19 K = 39.964000 p = H = 1.007825 40 20 Ca = 39.962591 n = 1.008665 It loses 0.00057 u of mass, so it gives off (0.00057)(931.5) =.53 MeV of energy This is exoergic

12. Hahn and Strassmann’s discovery TOC Fermi discovers that neutrons are the way to go, and discovers many nuclear reactions In 1938, Otto Hahn and Fritz Strassmann discover that Uranium will split in half: n + 235 92 U ---> 141 56 Ba + 92 36 Kr + 3n (typical) The reaction releases 200 MeV The neutrons released could trigger further fission

13. Hahn and Strassmann’s discovery TOC Scientists begin to realize that a chain reaction could lead to a very powerful explosion Demo - critical mass…

14. Einstein’s Letter to Roosevelt TOC In Summer 1939, US has no atomic energy program Hitler has halted sales of Czech Uranium Hitler classifies all nuclear research Hungarian Physicist Leo Szilard (and many others) worried Cannot convince Fermi Turns to Einstein Einstein returns from vacation, and writes a letter to Roosevelt

15. Einstein is a pacifist Einstein fears Hitler

16. US starts 1 day before Pearl Harbor bombing. (2 1 / 2 years later)

17. The Manhattan Project TOC Started in 1942 in Los Alamos NM Unprecedented rush to make a bomb Basic concept - Combining two sub critical masses: Explosive Uranium 235 Tube Separating U 235 from 238 by gaseous diffusion at Oak Ridge Feynman and the chemical engineer

18. Hiroshima and Nagasaki TOC At 8:15, August 6, 1945 The U.S. detonated a Uranium Fission bomb 1,900 feet above the city of Hiroshima. Near the end of WWII, the US had been bombing nearly every major city in Japan. For some reason, Hiroshima and Nagasaki had been spared. They had become refugee centers for those displaced by bombing elsewhere.

19. The devastation was nearly complete

20. About 100,000 people died immediately..

21. 45,000 more died later from the radiation

22. People were killed, and all the people who knew them as well

23. 3 days later, we dropped another bomb on the city of Nagasaki, killing 74,000 people,

24. This bomb was a plutonium bomb

25. Nagasaki’s rugged topography protected larger parts of the city from the direct blast.

26. Emperor Hirohito surrendered on September 2 Hindsight vs. foresight…

27. Nuclear Fusion - joining of Nuclei TOC Fusion powers the sun: Energy comes primarily from the Proton- Proton cycle: 1 H + 1 H = 2 H + e + + ν 1 H + 2 H = 3 He + γ 3 He + 3 He = 4 He + 1 H + 1 H (requires heat and pressure)

28. Nuclear Fusion - joining of Nuclei TOC Helium can also fuse: 4 He + 4 He = 8 Be + γ 4 He + 8 Be = 12 C + γ Carbon can fuse as well: 12 C + 12 C = 24 Mg + γ 16 O + 16 O = 28 Si + 4 He

29. The curve of binding energy TOC Binding energy per nucleon Going to more tightly bound releases energy A U235 bomb is technically difficult A Pu bomb is easy - not efficient? Most tightly boundFission releases energy Fusion releases energy

30. Nuclear power TOC Closed loop design No greenhouse gases emitted. What do you do with the waste?