Lecture 31 Chapter 22, Sections 3-5 Nuclear Reactions. Nuclear Decay Kinetics Fission Reactions Fusion Reactions

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Spencer Tyler
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1 Lecture Chapter, Sections -5 Nuclear Reactions Nuclear Decay Kinetics Fission Reactions Fusion Reactions

2 Gamma Radiation Electromagnetic photons of very high energy Very penetrating can pass through the human body Require thick layers of lead or concrete to be stopped Emitted from nuclei that have excess energy Usually from products of other nuclear decay 6 88 m 86 Ra Rn m Rn 4 α Rn γ 86 8m 84 Rn Po 8m Po 4 α Po γ Sometimes metastable (m) is denoted with a * meaning just excited

3 Belt of Stability

4 Identify the Product 58 Ce? 4 α 0%. Barium-9 0%. Barium-7 0%. Cerium-7 0% 4. Xenon-7 0% 5. Xenon-5 4 5

5 If 4 O undergoes electron capture, what is the product? 0%. Fluorine- 0%. Fluorine-4 0%. Nitrogen- 0% 4. Nitrogen-4 0% 5. Oxygen- 4 5

6 Rates of Decay Recall from Chapt 5 that nuclear decay is unimolecular First Order Rate = k concentration (or often # of nuclei) c = c ln c c 0 0 e kt = kt ln t N N 0 = ln k t ln = t

7 Some Everyday Decay Bananas K Ca β Typical banana contains about 400 mg of K Generates about decays per second 40 K half-life is,60,000,000 years Average adult male contains 40 g of K (4,400 decays per second) Fiesta ware Any old pottery with a deep orange/red color contains uranium oxide The Fiesta Ware collection (96-94) is particularly famous Luminescent dials Old (early 900 s) glow-in-the-dark dials contain radium paint Mostly replaced now by tritium

8 Induced Nuclear Reactions Reactions in which a nuclear projectile collides and reacts with another nucleus Neutron-Capture Reactions usually exothermic, the produced nuclide usually decays by proton or γ emission N 0n 7N 6C 4 m 5 7 N 0n 7N 6C 4 m Binuclear reactions collision of two nuclei at very high energy N α 9F 8O 4 m p p

Cyclotron a positive particle accelerator used to fabricate some of the unnatural elements.

9 Elements Z=4, 6, 85 and Z > 9 are not naturally occurring on Earth. They can be made from nuclear reactions. Cyclotron a positive particle accelerator used to fabricate some of the unnatural elements. Doesn t work well for heavy particles Linear accelerator a heavy-ion accelerator. Accelerators mainly used to study what happens during nuclear reactions. Making Synthetic Elements

10 Nuclear Fission Fission splits a nucleus into two fragments, which are themselves usually unstable The reaction also releases neutrons and loads of energy U 0 n 8 Xe Sr n The total energy released could be determined by the same kind of mass difference calculation we used earlier.

11 Nuclear Fission Critical Mass the amount of material that is just large enough to recapture one neutron for every fission reaction, thus causing another fission, which causes another, which Thus, fission becomes self-sustaining. Reaction growing exponentially = bomb

rate of fission is controlled by adjusting the number of recaptured neutrons with

12 Nuclear Reactors If number of neutrons absorbed can be carefully controlled, then the rate of reaction can be kept constant Constant release of energy = useful The rate of fission is controlled by adjusting the number of recaptured neutrons with Cd Moderator (water or graphite) slows neutrons smaller mass needed to become critical

13 Nuclear Fusion Fusion is easiest for lightest nuclides (smallest charge) Generates a small amount of radioactive by-products Fusion can be induced from a particle accelerator Small scale does not release useful amounts of energy Fusion begins when temperature is high enough to overcome Coulombic repulsion Not dependent on mass of reactants (i.e. no critical mass) So, just get some hot fusion! Easy! Critical temperature is 0 7 K The whole trick is to contain the fusion reaction 6 Li 0 n e e Fusion not contained == bomb Fusion bomb can be BIG because of lack of critical mass 5m 7m Li 4 4 e 0 n

14 Tokamak One solution is a toroid of magnets a tokamak reactor eat provided by electrical resistance, neutron beams and RF

15 Inertial Fusion Second possibility is to confine the plasma with the same beams that supply heat (laser or particle) Momentum of incoming beams holds fuel in place

Stellar Nuclear Reactions First-generation star Initial fuel almost entirely hydrogen Eventually creates elements up to iron (Z=6) Supernovae the explosion of a star

16 Stellar Nuclear Reactions First-generation star Initial fuel almost entirely hydrogen Eventually creates elements up to iron (Z=6) Supernovae the explosion of a star that ejects its nuclides into space. Second-generation stars create still-heavier elements Our sun is probably a third-generation star e Be e e e e m m γ β γ β

17 Today Finish CAPA #7 Wednesday Work on CAPA #8 REVIEW REVIEW REVIEW!!!

Lecture 35 Chapter 22, Sections 4-6 Nuclear Reactions. Fission Reactions Fusion Reactions Stellar Radiation Radiation Damage

Lecture 35 Chapter 22, Sections 4-6 Nuclear Reactions. Fission Reactions Fusion Reactions Stellar Radiation Radiation Damage Lecture 35 Chapter, Sections 4-6 Nuclear Reactions Fission Reactions Fusion Reactions Stellar Radiation Radiation Damage Induced Nuclear Reactions Reactions in which a nuclear projectile collides and reacts