PHY 114 A General Physics II 11 AM-12:15 PM TR Olin 101 Plan for Lecture 26 (Chapter 45): Some topics in nuclear physics 1. Nuclear reactions 2. Fusion reactors 3. Fission reactors Link to NCSU Professor Wesley Henderson's course materials on "Engineering Challenges at the Energy Frontier (includes fission reactors) http://www.che.ncsu.edu/ileet/che596web_fall2011/index.html 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 1
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General comments on final exam: It will be comprehensive May bring up to 4 equation sheets (turned in with exam papers) Need calculator; must not use cell phone, computer, etc. May pick up final exams from my office after they are graded A PHY 114 review session has tentatively been scheduled for Thursday 5/3/2012 at 11 AM in Olin 107 A. I plan to come B. I do not plan to come C. Other suggestions? 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 3
Other exams PHY114 A NOTE: Students should have no more than two exams in a 24-hour period. They should be allowed to reschedule exams in excess of two in a 24-hour period. 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 4
How many of you need to reschedule the final exam time: A. Happy to take the exam as scheduled (May 8) B. Entitled to reschedule according to WFU policy C. Not entitled, but would prefer to reschedule For those of you who need/would like to reschedule which time is likely to be preferable A. Prefer rescheduled time earlier than May 8 B. Prefer rescheduled time later than May 8 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 5
Webassign comments: 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 6
Typical reaction : (Reactants) (Products) + excess energy kinetic energy (eg. neutron production) excess energy = photon energy Assume that any available mass can be converted to energy according to E=mc 2. 1u = 1.660539 10 E u = m u c 2-27 kg = 1.660539 10 = 931.494 MeV -27 kg Need table of atomic mass numbers: http://www.nist.gov/pml/data/comp.cfm ( 8 2.99792 10 m/s) 2 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 7
Neutron 1.008655 u 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 8
Example: 1 1 H+ H He + γ Energy available to γ ray : 1 2 3 2 [ m( H) + m( H) m( He) ] c = [ 1.007825 + 2.014102 3.016029] 1 2 1 3 2 1 2 = 0.005878 931.494MeV = 5.475 MeV 931.494MeV In principle, nuclear energy is available in both fission and fusion reactions. 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 9
Fusion reactions Summary of reactions in the sun: Total energy release for each event: 26.7 MeV This process has been occurring for 5 x 10 9 years and is expected to last for 10 9 more years 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 10
Fusion reactions which might be possible on earth: 2 1 H + 2 1H 3 2He + n (Q=3.27 MeV) 2 1 H + 2 1H 3 2He + 1 1H (Q=4.03 MeV) 2 1 H + 3 1H 4 2He + n (Q=17.59 MeV) n + 6 3Li 4 2He + 3 1H (Q=4.78 MeV) Technological challenge: How to control the energetic reactants to effect net energy gain??? Magnetic confinement tokamak design Laser confinement high powered lasers focused on fuel put into solid form 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 11
5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 12
Fission Advantages Technology has been demonstrated Disadvantages Nuclear waste Fusion Less dangerous nuclear waste Technology has not yet been demonstrated 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 13
Nuclear power plant in France (photo from textbook) 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 14
Fission: Some history 1932 James Chadwick (England) discovered neutron Enrico Fermi (Italy) discovered that neutrons could be absorbed by nuclei to form new elements Lise Meitner, Otto Hahn, Fritz Strassmann, Otto Frisch (Germany) discovered fission of U Example: n+ 140 54 ( 14s) ( 64s) ( 13d) ( 40h) ( stable) 94 38 235 92 Sr U Xe 140 55 94 39 236 92 Cs Y U 94 40 140 54 140 56 Zr Ba ( 75s)( 19min)( stable) Xe+ 94 38 140 57 Sr + 2n La 140 58 Ce Q 200 MeV 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 15
Other decay products for n+ 235 92U 236 92 U 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 16
Mechanism for power plant Heat mechanical energy generator electricity Heat sources: Chemical burning: oxygen + coal, oil, etc. Nuclear burning: n + 235 92U neutrons generated in the reaction are also used to fuel the reaction 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 17
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Model for nuclear reactor accounting for 1000 neutrons (water) 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 19
Simplified model of nuclear power plant 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 20
Thermal power release by radioactive wastes from one year s operation of a typical large nuclear power plant 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 21
http://www.nei.org 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 22
http://www.gen-4.org 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 23
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Other uses of nuclear radiation Food irradiation: http://www.epa.gov/rpdweb00/sources/food_irrad.html Food irradiation is a technology for controlling spoilage and eliminating food-borne pathogens, such as salmonella. The result is similar to conventional pasteurization and is often called "cold pasteurization" or "irradiation pasteurization." Like pasteurization, irradiation kills bacteria and other pathogens, that could otherwise result in spoilage or food poisoning. The fundamental difference between the two methods is the source of the energy they rely on to destroy the microbes. While conventional pasteurization relies on heat, irradiation relies on the energy of ionizing radiation. The FDA emphasizes that no preservation method is a substitute for safe food handling procedures. 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 26
http://www.epa.gov/rpdweb00/sources/food_irrad.html 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 27
Measures of radiation: 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 28
Fundamental processes of radiation Nuclear reactions Move nuclei of atoms in materials (Ex: neutrons can cause crystal defects) Produce many electronic excitations excited and/or charged species undergo uncontrolled chemical reactions (Ex. Electrons and γ-rays are examples of effective ionizing radiation); the greater the energy the greater the potential radiation damage The least massive reaction products carry the most energy and are responsible for the most radiation effects 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 29
Energy analysis of a simple reaction : 222 88 Ra 86Rn + 226 4 2 He Q=4.87 MeV 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 30
Energy analysis of a simple reaction : 222 88 Ra 86Rn + 226 4 2 He Q=4.87 MeV p Q E Rn = He = p 2 Rn p 2m = Rn 2 He p 2m He + He 2 He p 2m = p He 2 p 2m 1 222 1/ 4 Q 1/ 222 + 1/ 4 u 0.98 Q 4.8MeV 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 31 = + 1 4 =
Other uses of nuclear radiation Carbon dating Living organisms have a ratio of 14 C / 12 C of 1.3x10-12 reflecting normal atmospheric processes. When an organism dies, the ratio is reduced due to the 5730 yr half-life of 14 C. Example from your textbook: A piece of charcoal containing 25 g of carbon is found to have an activity of 4.167 decays/s. How long ago did the tree live that produced this charcoal? Decay rate when tree was alive for 25 g of C : dn dt N 0 0 = = λn 25 12 0 λ = 6.022 10 ln2 5730 yr 3.1556 10 23 1.3 10 12 s/yr = 1.631 10 λn 6.25 decays/s 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 32 7 = 3.83 10 12 0 = 12 /s
dn dt N dn dt dn dt Other uses of nuclear radiation Carbon dating -- continued Decay rate when tree was alive for 25 g of 0 0 = = λn 25 12 6.022 10 Current decay rate : 0 = e λt 0 λ = ln2 5730 yr 3.1556 10 t 23 = 1.3 10 dn dt = λn 1 3.83 10 12 0 e 12 = 1.631 10 -λλ ln /s s/yr 4.1667decays/s 6.25 4.17 λn = 1.06 10 6.25 decays/s 5/1/2012 PHY 114 A Spring 2012 -- Lecture 26 33 = 7 C : 12 = 3.83 10 0 = 12 11 /s s = 3400yr