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Resonance Reactions

Resonance Reactions. HW 34. In the 19 F ( p , ) reaction: The Q-value is 8.??? MeV. The Q-value for the formation of the C.N. is 12.??? MeV. For a proton resonance at 668 keV in the lab system, the corresponding energy level in the C.N. is at 13.??? MeV.

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Resonance Reactions

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  1. Resonance Reactions HW 34 • In the 19F(p,) reaction: • The Q-value is 8.??? MeV. • The Q-value for the formation of the C.N. is 12.??? MeV. • For a proton resonance at 668 keV in the lab system, the corresponding energy level in the C.N. is at 13.??? MeV. • If for this resonance the observed gamma energy is 6.13 MeV, what is the corresponding alpha particle energy? • If for this resonance there has been no gamma emission observed, what would then be the alpha particle energy? Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).

  2. Neutron Resonance Reactions Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).

  3. Neutron Activation Analysis (Z,A) + n (Z, A+1) -  (-delayed -ray) (Z+1, A+1) http://ie.lbl.gov/naa Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).

  4. Neutron Attenuation Neutrons Target Thickness “x” Similar to -attenuation. Why? Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).

  5. Neutron Moderation HW 35 Show that, after elastic scattering the ratio between the final neutron energy E\ and its initial energy E is given by: For a head-on collision: After ns-wave collisions: where Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).

  6. Neutron Moderation HW 35 (continued) How many collisions are needed to thermalize a 2 MeV neutron if the moderator was: 1H 4He 238U Discuss the effect of the thermal motion of the moderator atoms. Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).

  7. Nuclear Fission Surface effect Coulomb effect ~200 MeV  Fission Fusion  Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).

  8. Nuclear Fission • B.E. per nucleon for 238U (BEU) and 119Pd (BEPd) ? • 2x119xBEPd – 238xBEU = ?? K.E. of the fragments  1011J/g • Burning coal  105J/g • Why not spontaneous? • Two 119Pd fragments just touching  The Coulomb barrier is: • Crude …! What if 79Zn and 159Sm? Large neutron excess, released neutrons, sharp potential edge…! Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).

  9. Nuclear Fission • 238U (t½ = 4.5x109 y) for -decay. • 238U (t½ 1016 y) for fission. • Heavier nuclei?? • Energy absorption from a neutron (for example) could form an intermediate state  probably above barrier  induced fission. • Height of barrier above g.s. is called activation energy. Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).

  10. Nuclear Fission Liquid Drop Shell Activation Energy (MeV) Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).

  11. Nuclear Fission = Volume Term (the same) Surface Term Bs = - as A⅔ Coulomb Term BC = - aC Z(Z-1) / A⅓  fission  Crude: QM and original shape could be different from spherical. Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).

  12. Nuclear Fission Consistent with activation energy curve for A = 300. Extrapolation to 47  10-20 s. Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).

  13. Nuclear Fission 235U + n  93Rb + 141Cs + 2n Not unique. Low-energy fission processes. Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).

  14. Nuclear Fission Z1 + Z2 = 92 Z1  37, Z2  55 A1 95, A2  140 Large neutron excess Most stable: Z=45 Z=58  Prompt neutrons within 10-16 s. Number depends on nature of fragments and on incident particle energy. The average number is characteristic of the process. Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).

  15. Nuclear Fission The average number of neutrons is different, but the distribution is Gaussian. Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).

  16. Higher than Sn? Delayed neutrons ~ 1 delayed neutron per 100 fissions, but essential for control of the reactor. Follow -decay and find the most long-lived isotope (waste) in this case. Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).

  17. Nuclear Fission Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).

  18. Nuclear Fission 1/v Fast neutrons should be moderated. 235U thermal cross sections fission  584 b. scattering  9 b. radiative capture  97 b. Fission Barriers Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).

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