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

2. 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 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, (Saed Dababneh).

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

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

5. 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, (Saed Dababneh).

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

7. 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, (Saed Dababneh).

8. Nuclear Fission Fissile Fissionable
Q for 235U + n  236U is 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 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, (Saed Dababneh).

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

10. 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 Cs n
23592U + 10n ► 8735Br La n
23592U + 10n ► 7230Zn Sm + 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, (Saed Dababneh).
Nuclear Reactor Theory, JU, Second Semester, (Saed Dababneh). 10