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Lecture II. 2 The basics of nuclear reactions

Lecture II. 2 The basics of nuclear reactions. Alexandru Negret. Lecture II.2 – Nuclear Reactions A. Negret. Outline. Nuclear reaction kinematics Conservation laws: energy, momentum, angular momentum, parity Reaction mechanisms Nucleosynthesis Cross section databases.

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Lecture II. 2 The basics of nuclear reactions

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  1. Lecture II.2The basics of nuclear reactions Alexandru Negret

  2. Lecture II.2 – Nuclear Reactions A. Negret Outline • Nuclear reaction kinematics • Conservation laws: energy, momentum, angular momentum, parity • Reaction mechanisms • Nucleosynthesis • Cross section databases

  3. Lecture II.2 – Nuclear Reactions A. Negret Nuclear reaction kinematics b Y X a projectile target recoil ejectile X(a,b)Y pb q pa pY

  4. Lecture II.2 – Nuclear Reactions A. Negret Conservation laws: The energy X(a,b)Y mac2+mXc2+Eka = mbc2+mYc2+Ekb+EkY+eb+eY Q = Ekfinal – Ekinitial = mac2 + mXc2 - mbc2 - mYc2 Reaction energy (Q-value) Eth = - Q (ma+mX) / mX Reaction threshold (only if Q<0) QUESTION: Why is the reaction threshold larger than Q?

  5. Lecture II.2 – Nuclear Reactions A. Negret Conservation laws: The momentum X(a,b)Y pb pa = pb + pY q pa pY2 = pa2 + pb2 – 2papbcosq pY The angular momentum Center – of – mass system: IX + Sa + LaX = IY + Sb + LbY The parity PaPX(-1)L_aX = PbPY(-1)L_bY

  6. Lecture II.2 – Nuclear Reactions A. Negret Reaction mechanisms Reaction mechanisms: • COMPOUND NUCLEUS @ Low interaction energy (Bohr postulate) • PRE-EQUILIBRIUM • DIRECT REACTION Examples: • Elastic scattering (shape elastic / compound elastic): (n, n), (a, a) • Inelastic scattering: (p,pg), (n,ng) • Coulex (Coulomb excitation) • Charge exchange reaction: (p,n), (n,p) • Transfer reaction: Stripping: (d,n), (d,p) • Transfer reaction: Pick-up: (p, d) • Capure: (n,g), (p,g) • Fragmentation: 48Ca + Be -> 44S + … -> RIB, GSI – FRS • Spallation: p(1.4 GeV @ ISOLDE) + 238U -> RIB, CERN – ISOLDE • Fission: 235U(n,F) • Fusion: 12C(a, g)16O; d + t -> a + n

  7. Lecture II.2 – Nuclear Reactions A. Negret Exercise: guess the reaction type 28Si(p, p)28Si Elastic / inelastic scattering 12C(a, 3He)13C Stripping 14N(d, 2He)14C Charge exchange 194Pt(6Li, 3n)197Tl Fusion-evaporation • Elastic scattering (shape elastic / compound elastic): (n, n), (a, a) • Inelastic scattering: (p,pg), (n,ng) • Coulex (Coulomb excitation) • Charge exchange reaction: (p,n), (n,p) • Transfer reaction: Stripping: (d,n), (d,p) • Transfer reaction: Pick-up: (p, d) • Capure: (n,g), (p,g) • Fragmentation: 48Ca + Be -> 44S + … • Spallation: p(1.4 GeV @ ISOLDE) + 238U • Fission: 235U(n,F) • Fusion: 12C(a, g)16O; d + t -> a + n

  8. Lecture II.2 – Nuclear Reactions A. Negret Nucleosynthesis Where are the nuclei formed? 1. During the Big Bang: H, He, very little amounts of Li, Be, B 2. In stars, through fusion: elements lighter than 56Fe (Why 56Fe?) • CNO cycle: Nuclear fusion process of H occuring in stars and using C, N, and O. • S-process: Sequence of n-capture reactions followed by beta decays producing elements heavier than Fe in the stars. 3. During the final explosion of a big star – Supernovae: elements heavier than 56Fe, but also lighter elements: 24Mg – 60Ni. • R-process: Sequence of n-capture reactions followed by beta decays producing heavy elements during the explosion.

  9. Lecture II.2 – Nuclear Reactions A. Negret Reaction databases • Evaluated (theoretical) databases: • ENDF/B-VII.1 (USA) • JEFF-3.1 (Europe) • JENDL-4.0 (Japan) • CENDL-3.1 (China) • ROSFOND (Russia) • Experimental databases: • EXFOR http://www.nndc.bnl.gov/exfor/endf00.jsp

  10. Lecture III.1 – Nuclear Reactions A. Negret Summary • Nuclear reaction kinematics • Conservation laws: energy, momentum, angular momentum, parity • Reaction mechanisms • Nucleosynthesis • Cross section databases

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