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Nuclear Fission 235 U + n 93 Rb + 141 Cs + 2 n Not unique. Low-energy fission processes. 1Nuclear Reactor Theory, JU, Second Semester, 2008-2009 (Saed.

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Presentation on theme: "Nuclear Fission 235 U + n 93 Rb + 141 Cs + 2 n Not unique. Low-energy fission processes. 1Nuclear Reactor Theory, JU, Second Semester, 2008-2009 (Saed."— Presentation transcript:

1 Nuclear Fission 235 U + n 93 Rb Cs + 2 n Not unique. Low-energy fission processes. 1Nuclear Reactor Theory, JU, Second Semester, (Saed Dababneh).

2 Nuclear Fission Z 1 + Z 2 = 92 Z 1 37, Z 2 55 A 1 95, A Large neutron excess Most stable: Z=45Z=58 Prompt neutrons Prompt neutrons within s. Number depends on nature of fragments and on incident neutron energy. The average number is characteristic of the process. 2Nuclear Reactor Theory, JU, Second Semester, (Saed Dababneh).

3 Nuclear Fission The average number of neutrons is different, but the distribution is Gaussian. 3Nuclear Reactor Theory, JU, Second Semester, (Saed Dababneh).

4 4 Why only left side of the mass parabola?

5 Delayed neutrons Higher than S n ? ~ 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. 5Nuclear Reactor Theory, JU, Second Semester, (Saed Dababneh). Waste. Poison. In general, decay favors high energy.

6 Nuclear Fission 6Nuclear Reactor Theory, JU, Second Semester, (Saed Dababneh).

7 Nuclear Fission 1/ v 235 U thermal cross sections fission 584 b. scattering 9 b. radiative capture 97 b. Fast neutrons should be moderated. Fission Barriers 7Nuclear Reactor Theory, JU, Second Semester, (Saed Dababneh).

8 8 Nuclear Fission Q for 235 U + n 236 U is MeV. Table 13.1 in Krane: Activation energy E A for 236 U 6.2 MeV (Liquid drop + shell) 235 U can be fissioned with zero-energy neutrons. Q for 238 U + n 239 U is 4.??? MeV. E A for 239 U 6.6 MeV MeV neutrons are needed. Pairing term: = ??? (Fig in Krane). What about 232 Pa and 231 Pa ? (odd Z). Odd-N nuclei have in general much larger thermal fission cross sections than even-N nuclei (Table 13.1 in Krane). Nuclear Reactor Theory, JU, Second Semester, (Saed Dababneh).

9 9 Nuclear Fission f,Th x b Why not use it?

10 10 Nuclear Fission Nuclear Reactors, BAU, 1 st Semester, (Saed Dababneh). Thermal neutron fission of 235 U forms compound nucleus that splits up in more than 40 different ways, yielding over 80 primary fission fragments (products) U n Rb Cs n U n Br La n U n Zn Sm n 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. 10Nuclear Reactor Theory, JU, Second Semester, (Saed Dababneh).


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