Nuclear Fission 235U + n  93Rb + 141Cs + 2n Not unique.

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Presentation transcript:

Nuclear Fission 235U + n  93Rb + 141Cs + 2n Not unique. Low-energy fission processes. Nuclear Reactor Theory, JU, Second Semester, 2008-2009 (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 neutron energy. The average number is characteristic of the process. Nuclear Reactor Theory, JU, Second Semester, 2008-2009 (Saed Dababneh).

Nuclear Fission The average number of neutrons is different, but the distribution is Gaussian. Nuclear Reactor Theory, JU, Second Semester, 2008-2009 (Saed Dababneh).

Why only left side of the mass parabola? Nuclear Reactor Theory, JU, Second Semester, 2008-2009 (Saed Dababneh).

In general,  decay favors high energy. Higher than Sn? Delayed neutrons ~ 1 delayed neutron per 100 fissions, but essential for control of the reactor. In general,  decay favors high energy. Waste. Poison. Follow -decay and find the most long-lived isotope (waste) in this case. Nuclear Reactor Theory, JU, Second Semester, 2008-2009 (Saed Dababneh).

Nuclear Fission Nuclear Reactor Theory, JU, Second Semester, 2008-2009 (Saed Dababneh).

Nuclear Fission 1/v 235U thermal cross sections fission  584 b. Fast neutrons should be moderated. 235U thermal cross sections fission  584 b. scattering  9 b. radiative capture  97 b. Fission Barriers Nuclear Reactor Theory, JU, Second Semester, 2008-2009 (Saed Dababneh).

Nuclear Fission Fissile Fissionable Q for 235U + n  236U is 6.54478 MeV. Table 13.1 in Krane: Activation energy EA for 236U  6.2 MeV (Liquid drop + shell)  235U can be fissioned with zero-energy neutrons. Q for 238U + n  239U is 4.??? MeV. EA for 239U  6.6 MeV  MeV neutrons are needed. Pairing term:  = ??? (Fig. 13.11 in Krane). What about 232Pa and 231Pa? (odd Z). Odd-N nuclei have in general much larger thermal fission cross sections than even-N nuclei (Table 13.1 in Krane). Fissionable Nuclear Reactor Theory, JU, Second Semester, 2008-2009 (Saed Dababneh).

Nuclear Fission Why not use it? f,Th 584 2.7x10-6 700 0.019 b Nuclear Reactor Theory, JU, Second Semester, 2008-2009 (Saed Dababneh).

Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh). Nuclear Fission Thermal neutron fission of 235U forms compound nucleus that splits up in more than 40 different ways, yielding over 80 primary fission fragments (products). 23592U + 10n ► 9037Rb + 14455Cs + 210n 23592U + 10n ► 8735Br + 14657La + 310n 23592U + 10n ► 7230Zn + 16062Sm + 410n ! The fission yield is defined as the proportion (percentage) of the total nuclear fissions that form products of a given mass number. Revisit thermal and look for fast. Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh). Nuclear Reactor Theory, JU, Second Semester, 2008-2009 (Saed Dababneh). 10