1. Compound nucleus reactions Consider the data Propose a model

2. Consider these data…

3. Same final state; different initial state Varying energies for p and 

4. Consider these data… All reactions have the same intermediate (compound) nucleus. Each initial state can produce all three final states The cross section for each final state does not depend on the initial reactants. (data) The cross section for producing each final state depends on the excitation energy in the compound nucleus.

5. Compound nucleus model Consider these reactions as a two-stage processes: Decay of the compound nucleus Formation of the compound nucleus a + X  [C*]  Y + b

6. Compound nucleus model The lifetime  C* of the compound nucleus is long compared to the time for the incident energy to be shared among nucleons.  C* C* is almost always formed in an excited state.  Nucleus C* retains no “memory” of how it was formed.  Particle a has multiple scatters (energy exchanges) with nucleons in the target nucleus. T a is shared quickly.

7. Compound nucleus model After a “long” time, C* decays, emitting one or more particles.  C* The decay mechanism (channel) that dominates the decay of C* is determined by the excitation energy E* in C* (data)

8. m d c 2 + m Li c 2 E* m Be c 2 0.0 m  c 2 + m  c 2

9. m a c 2 + m X c 2 E* m C* c 2 0.0 m b c 2 + m Y c 2 Compound nucleus model

10. Decay of the compound nucleus Formation of the compound nucleus What is the form for these?

11.  Resonances m In-116 c 2 m n c 2 + m In c 2 m In-116 c 2 E*E* 0 Ti*Ti* Tf*Tf* TOF Exp’t

12. Time of Flight Experiment t = L/v Measure t  you know v Maxwell velocity neutron beam shutter Target/detector L tt gate Cd  Example

13. Compound nucleus model Decay of the compound nucleus Formation of the compound nucleus

14. Compound nucleus model Include spin effects