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
Nuclear reactions TOC Charge and nucleon number are conserved Can be written as follows: 4 2 He N ---> 17 8 O 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
Nuclear reactions - example TOC What’s the initial nucleus? ??? + n ---> p C ??? (n, p) 14 6 C ? ? XX n ---> 1 1 p C 14 7 N
Whiteboards: Nuclear Reactions 11 | 2 | 3 | 4234 TOC
W Ba(n, ) ??? (hint) Ba 0 0 Ba n ---> 0 0 + ? ? XX Ba
W Ba(n, ?) Cs p Ba n ---> ? ? XX Cs 11p11p
W 2 1 H(d, ?) 4 2 He (1 hint) 21d21d 2 1 H H ---> ? ? XX He 0000
W Au( , d) ??? (2 hints) Hg 4242 2 1 d Au ---> 2 1 d + ? ? XX Hg
W 9 4 Be(?, t) 8 4 Be (1 hint) 21d21d 3 1 t 9 4 Be + ? ? XX ---> 3 1 t Be 21d21d
W Is this reaction exoergic or endoergic? What energy does it require or give off? Au( , d) Hg Au = = He = total = Hg = d = 2 H = total = It gains u of mass, so it requires ( )(931.5) = MeV of energy This is endoergic
W exo.53 MeV Try this reaction - is it endo or exo, and how much? K(p, n) Ca K = p = H = Ca = n = It loses u of mass, so it gives off ( )(931.5) =.53 MeV of energy This is exoergic
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 U ---> Ba Kr + 3n (typical) The reaction releases 200 MeV The neutrons released could trigger further fission
Hahn and Strassmann’s discovery TOC Scientists begin to realize that a chain reaction could lead to a very powerful explosion Demo - critical mass…
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
Einstein is a pacifist Einstein fears Hitler
US starts 1 day before Pearl Harbor bombing. (2 1 / 2 years later)
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
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.
The devastation was nearly complete
About 100,000 people died immediately..
45,000 more died later from the radiation
People were killed, and all the people who knew them as well
3 days later, we dropped another bomb on the city of Nagasaki, killing 74,000 people,
This bomb was a plutonium bomb
Nagasaki’s rugged topography protected larger parts of the city from the direct blast.
Emperor Hirohito surrendered on September 2 Hindsight vs. foresight…
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)
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
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
Nuclear power TOC Closed loop design No greenhouse gases emitted. What do you do with the waste?