1. Nuclear Reactions --Part 2
Lesson 11
Nuclear Reactions --Part 2

2. Compound Nuclear Reactions
The compound nucleus is a long-lived reaction intermediate that is formed by a complex set of interactions between the projectile and the target.
The projectile and target nuclei fuse and the energy of the projectile is shared among all the nucleons of the composite system.
The lifetime of the CN is ~ s. This lifetime is directly measurable by crystal-blocking techniques.

3. Independence Hypothesis or “Amnesia Assumption”
The mode of decay of the CN is independent of its mode of formation.
Caveat: Conservation laws apply.
Experimental evidence: the Ghoshal expt.
Angular distributions symmetric about 90 in CN frame.

4. 62Cu>63Zn>62Ni
ang. mom effects

5. Cross Sections--General

6. Cross Sections--Energy Dependence

7. /D << 1 For reaction a + A Cb + B
Applying this to (n,) reactions

9. /D >>1
For reaction a + A Cb + B
ab = C PC(b)

10. /D >>1 Assumption is that of statistical equilibrium
For reaction a + A Cb + B
ab = C PC(b)
So the problem is to calculate the probability that C will decay to B + b.

11. Level densities

12. If emitted particles are neutrons

13. If emitted particles are charged particles

14. Excitation functions

15. Photonuclear Reactions

16. Photonuclear Reactions
GDR-- a giant oscillation of the nuclear protons vs the nuclear neutrons
dipole sum rule

17. Heavy Ion Reactions Classical motion
Dominated by high angular momentum
Aproj > 4

18. Mechanisms

19. Mechanisms

20. Elastic scattering

22. Fusion

26. Deep Inelastic Scattering

27. High Energy Reactions Low energy (< 10 MeV/A)
Intermediate Energy ( MeV/A)
High Energy (>250 MeV/A)

28. Spallation

29. New high energy mechanisms
Spallation
IMF formation
Cascade processes
Participant-Spectator Picture

30. Cascades
nucleon-nucleon
collisions

31. Participant-Spectator Physics

32. Multifragmentation
“Multifragmentation” refers to central collisions where several IMFs are emitted.
Caloric curve