Neutron Resonance Reactions

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Presentation transcript:

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

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).

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

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 n s-wave collisions: where Lethargy? Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

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).

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

Nuclear Fission B.E. per nucleon for 238U (BEU) and 119Pd (BEPd) ? 2x119xBEPd – 238xBEU = ??  K.E. of the fragments   1011 J/g Burning coal  105 J/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).

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).

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

Nuclear Fission =  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).

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).

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

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).

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).

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).

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