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Neutron Resonance Reactions

Neutron Resonance Reactions. Neutron Activation Analysis. ( Z,A ) + n  ( Z , A+1 ).  -.  (-delayed -ray). ( Z+1 , A+1 ). Neutron Attenuation. Neutrons. Target Thickness “x”. Similar to -attenuation. Why?. Neutron Moderation. HW 44.

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Neutron Resonance Reactions

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  1. Neutron Resonance Reactions Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

  2. Neutron Activation Analysis (Z,A) + n (Z, A+1) -  (-delayed -ray) (Z+1, A+1) Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

  3. Neutron Attenuation Neutrons Target Thickness “x” Similar to -attenuation. Why? Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

  4. Neutron Moderation HW 44 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 Lethargy? Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

  5. Neutron Moderation HW 44 (continued) How many collisions are needed to thermalize a 2 MeV neutron if the moderator was: 1H 2H 4He 12C 238U Discuss the effect of the thermal motion of the moderator atoms. Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

  6. Nuclear Fission Surface effect Coulomb effect ~200 MeV  Fission Fusion  Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

  7. 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…! Crude! Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

  8. 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 is called activation energy. Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

  9. Nuclear Fission Liquid Drop Shell Activation Energy (MeV) Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

  10. 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, First Semester, 2007-2008 (Saed Dababneh).

  11. Nuclear Fission Consistent with activation energy curve for A = 300. Extrapolation to 47  10-20 s. Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

  12. Nuclear Fission 235U + n  93Rb + 141Cs + 2n Not unique. Low-energy fission processes. Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

  13. 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, First Semester, 2007-2008 (Saed Dababneh).

  14. Nuclear Fission The average number of neutrons is different, but the distribution is Gaussian. Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

  15. 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, First Semester, 2007-2008 (Saed Dababneh).

  16. Nuclear Fission Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

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