Lecture15NuclearReactions_001

Lecture15NuclearReactions_001 - Lecture 15: Nuclear...

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Lecture 15: Nuclear Reactions RELEVANCE : Basic Research reaction mechanisms s t r u c t u r e exotic nuclei Applications: analytical tool – neutron activation analysis astrophysics – origin of elements space radiation effects satellites, Mars landing m a t e r i a l s s c i e n c e T c (high) superconductors medical therapy tumor treatment nuclear power – 25% of U.S. electricity DEFINITION: A collision between two nuclei that produces a change in the nuclear composition and/or energy state of the colliding species ; i . e . , 2 nd order kinetics 1. Nomenclature A. Constituents 1. Projectile: nucleus that is accelerated (v > 0) ; 0 2 10 12 eV a. neutrons – reactors b. light ions – A 4: AGS (NY), FNAL (IL) c. heavy ions – A > 4 U: ANL (IL), MSU (MI), TAMU (TX), RHIC (NY) d. electrons (and photons) SLAC (CA), CEBAF (VA), MIT (MA) e. exotic beams: , K, p : FNAL f. radioactive beams: MSU, ANL (IL) HHJRF (TN) 2. Target: fixed (v = 0), usually But now have colliding beams, RHIC, FNAL
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3. Products ANYTHING PERMITTED BY CONSERVATION LAWS. Note: since projectile kinetic energy can be converted into mass, only limit on mass-energy is beam energy. B. Notation: Target [projectile, light product(s)] heavy product e . g . , 3 7 82 208 Li + Pb C. Energetics: Q-values revisited 1 . Q =  (reactants)  (products) = available energy 2. Example: 208 Pb( 7 Li, ) reaction: Q = ( 208 Pb) + ( 7 Li) ( 215 At) ( , ) Q = 21.759 + 14.908 ( 1.263) 0 Q = 5.589 MeV ENDOTHERMIC Accelerate 7 Li to 5.589 MeV, no reaction. WHY? II. Energetic Conditions for Reaction A. Energetic Threshold: E th & Excitation Energy: E* 1. DEFINITION: E th is the minimum projectile energy necessary to satisfy mass-energy and momentum conservation (i.e., compensate for Q) 215 At + : 208 Pb( 7 Li, ) 215 At 212 At + 3n : 208 Pb( 7 Li, 3n) 212 At 197 Au + 18 C : 208 Pb( 7 Li, 18 C) 197 Au fission : 208 Pb( 7 Li, f)
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2. Derivation: a. Apply conservation Laws projectile + target composite nucleus products Mass-energy: E p + p + t = CN + E CN + E* E p = projectile E T = 0 kinetic energy E* = Excitation energy; When E* = 0 E p = E th 2 2 2 ; 2 mE p m p E Linear Momentum:
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Lecture15NuclearReactions_001 - Lecture 15: Nuclear...

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