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What have we learned last time?

What have we learned last time?. Q value Binding energy Semiempirical binding energy formula Stability. Nuclear Reactions. Scattering Reactions. Elastic scattering A(a,a)A Inelastic scattering A(a,a’)A*. Other reactions. Energetics of nuclear reactions.

thomas-kirby
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What have we learned last time?

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  1. What have we learned last time? • Q value • Binding energy • Semiempirical binding energy formula • Stability

  2. Nuclear Reactions

  3. Scattering Reactions • Elastic scattering A(a,a)A • Inelastic scattering A(a,a’)A*

  4. Other reactions

  5. Energetics of nuclear reactions • Energy, mass number, momentum conservation • Q-value : positive exoergic; negative endoergic • Example of endoergic 14N + 4He  1H + 17O + Q Q = -1.19 MeV Is it enough to start the reaction?

  6. Momentum correction

  7. Coulomb barrier correction 14N + 4He  1H + 17O + Q Threshold energy in SL: 3.6 MeV [(4+14)/14] = 4.6 MeV

  8. Cross section • Symbol σ • Geometrical cross section σ = π (Rtarget)2 10-24 cm2 Barn, 1 b = 10-24 cm2 = 100 fm2 1 mb = 10-27 cm2 1 μm = 10-30 cm2

  9. Measurements of cross sections • Thin targets • Thick targets

  10. Compound Nucleus Reactions 3-4 MeV/A yrast line – lowest energy for a given angular momentum

  11. Discovery of Fission Until 1938 all scientists believed that the elements with Z > 92 (transuranium elements) arise when uranium atoms are bombarded with neutrons. • 1938 • average number of 2.4 neutrons. • statistical phenomenon, Gaussian distribution, independent of the fissioning nucleus. 1944 Nobel Prize in Chemistry for Otto Hahn "for his discovery of the fission of heavy atomic nuclei” Otto Hahn and Lise Meitner, 1913, at the KWI for Chemistry in Berlin

  12. Radioactive Decay Processes These radioactive products are the waste products of nuclear reactors.

  13. Mass Distribution of Fission The fragments in the vicinity of A = 95 and A = 140 share 92 protons. Prompt neutrons are emitted in 10-16 s. Delayed neutrons intensity 1 in 100 fissions or 0.02 neutrons per fission (from neutron emission). Delayed neutrons are essential for controlling the reactors. 95 140 symmetric Source: University of Waterloo

  14. Neutron Cross Sections for fission of U and Pu 1/v -dependence 1 b = 10-28 m2; 1 MeV = 1.6 x 10-13 J Source: World Nuclear Association

  15. Binding energy per nucleon http://hyperphysics.phy-astr.gsu.edu/

  16. Q-value Energy released in a nuclear reaction (> 0 if energy is released, < 0 if energy is used) Example: The sun is powered by the fusion of hydrogen into helium: 4p  4He + 2 e+ + 2ne Mass difference dMreleased as energydE = dM x c2

  17. Fusion Reaction

  18. How Do We Produce Exotic Nuclei?

  19. N=Z ? 60 61 59 Zn 58 30 58 60 59 57 Cu 29 56 57 59 58 Ni 28 28 29 30 31 58Zn and the rp-process • no excited states in Z > N • mirror symmetry • 59Zn-59Cu • 58Zn-58Cu • rp-process • Spectroscopic Information • 58Zn (Z=30, N=28) • no excited states, spin and parity • predicted from 58Ni • Astrophysics • rp-process: • hot and explosive hydrogen burning • environments (X-ray burst) • stops at 56Ni? • beyond 56Ni: 56Ni(p,γ)57Cu(p,γ)58Zn • rates 56Ni(p,γ)57Cu; spectroscopy of 57Cu • rates 56Ni(d,p); spectroscopy of 57Cu • 57Cu(p,γ)58Zn – no information • calculations based on 58Ni-58Zn mirror symmetry

  20. 58Zn28 36Ar + 24Mg → 60Zn*→ 58Zn + 2n s(2n) < 20 μb (20 x 10-34 m2) Spokespersons: C. Andreoiu and P.E. Garrett, University of Guelph @ Argonne National Laboratory, Chicago, 2006

  21. Gammasphere + Ancillary Detectors • Gammasphere • (100 Ge detectors) • MICROBALL • (95 CsI) • 20 neutron detectors

  22. Particle Detectors - MICROBALL • 95 CsI detectors • average efficiency • 80% alphas • 70% protons D.G. Sarantites et al. Nucl. Instrum. Meth. A 400, 87 (1997)

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