Energy dissipation versus massasymmetry in fission

1
PART 2 - THE CROSS SECTION
The nuclear structure effects can be quantified
in fission cross-section at low energies.
Structural energy variations produce many
excitations responsible for different resonances
in the cross-section.
2
In fission, the whole nuclear system is
characterized by some collective variables
which determine approximately the behavior of
many other intrinsic variables.
3
Nuclear shape parameterization
Most important degrees of freedom encountered in
fission -elongation -necking-in -mass-asymmetry
(a) Diamond-like (swollen) shapes (b) Necked
shapes
4
Potential Energy and theTrajectory in the
Configuration Space
235U -gt 100Sr135Xe
5
Single-particleLevels
235U experimental sequence of levels 7/2-,
1/2,3/2 in the first well.
6
Landau-Zener transitions
7
Landau-Zener equations
8
Theoretical Barrier and Excitation Levels
Excitations in the frame of the superfluid model
9
Phenomenological Barrier with Theoretical
Excitations
10
Double Humped Barrier Resonance and Imaginary
Potential
RP1/P2 P1PD/(PDPa) P2PB/(PnPgPAPB) P1f(W)
W depends on the spin J of the nucleus
11
Theoretical Determination of the Imaginary Values
12
Resonance due to the spin 1/2 levels
Intermediate resonance peaks similar to those
obtained within a triple humped barrier
13
Details of calculation - Cross-section
Formation of compound nucleus at a given
excitation energy and spin
Detailed balance principle
Disintegration energy widths
14
The nuclear densities
15
Cross section for 235U with 135Xe heavy fragment
16
(No Transcript)
17
(No Transcript)
18
CONCLUSIONS
It is possible that the rich resonant structure
of the fission cross section is due to
rearrangements of orbitals and the dynamics of
the process, beginning with the ground state and
reaching the scission. A large number of
different barriers are formed leading to a large
number of resonance formed in the second well.
So, the resonances carry information about the
structure of the nucleus and the dynamics.
19
Example Th anomaly
231Th-gt 100Zr 131Sn
20
(No Transcript)
21
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
232Th neutron-induced fission cross section