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2010 PHYSICS 002C Lecture 27

# 2010 PHYSICS 002C Lecture 27 - PHYSICS 002C Lecture 27 June...

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PHYSICS 002C Lecture 27 June 2, 2010 Serway and Jewett Chapter 30 – Fission and Fusion Nuclear energy means transmuting an element from the less stable ends of Fig 30.9 towards the stable middle portion. Q : Why does the common phrase “atomic energy” mean conventionally? (a) Chemical energy from joining atoms like C and O; (b) Energy derived from changes to the nuclei of atoms; (c) Small amounts of energy; (d) Quantized energy; (e) Einstein’s concept of photons. According to the figure, U 235 can give off about 1 MeV per nucleon by breaking up into 2 lighter components like 96 Sr 38 and 136 Xe 54 plus 3 neutrons. Q : Since 1 nucleon has a mass of about 938 MeV, the fission energy yield is about 1 Mev per 938 MeV = 10 3 of the rest energy. What is the amount of energy that could be obtained from the complete fissioning of 10 kg 235 U? J 10 ) s m 10 3 ( kg 10 10 001 . 0 15 2 -1 8 3 2 Mc E (a) 10 12 J; (b) 10 13 J; (c) 10 14 J; (d) 10 15 J; (e) 10 16 J Fusing protons to make He 4 is too hard for Earthlings. It is much easier to fuse deuterons to get 6 MeV per nucleon or 0.6%M 2 c . Actually that is too hard also, so we fuse deuterons and tritons D+T He 4 +n 0 + 17.5 meV Q: What is the ratio of the neutron velocity to that of the He 4 nucleus? (a) 1 ; (b) 2 ; (c) 4; (d) 8; (e) 16 Q: What is the kinetic energy of the neutron? (a) 0.875 ; (b) 1.75 ; (c) 3.5; (d) 7; (e) 14 MeV Sadly, you have to make the tritium in a reactor. This is expensive and makes break-even difficult to achieve. If the neutrons are captured in low Z material like sand, fusion could be safer than fission because there wouldn’t be long lived radioactive waste. 1

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Outline 1. Fission and fusion 2. Introduction 3. Fallout and background 4. Radioactive decay and unpredictability 5. Alpha particle decay 6. Beta decay and neutrinos, observation of neutrinos 7. Nuclear reactors – Enrico Fermi’s pile. 8. Controlled Fusion 9. Attempting to solve the energy problem On Thursday Oct 16, 1980 China conducted its last atmospheric nuclear bomb test. The next Monday probably, Terry Kovacs at Bell Labs found radioactivity on his shoes after walking through some wet leaves during the lunch break and became worried that his Ge-70 source was leaking at Bell Labs. Guessing that 1 micro Curie had collected from 10 m 2 of rain water, the total activity dispersed into the atmosphere would have been MCi 50 Ci/m 10 ) m 10 37 . 6 ( 4 2 7 2 6 . A fission bomb needed to start an H bomb needs a yield of about 20 kt of
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2010 PHYSICS 002C Lecture 27 - PHYSICS 002C Lecture 27 June...

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