Compound nucleus reactions

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

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

6. C* 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. • Particle a has multiple scatters (energy exchanges) with nucleons in the target nucleus.Tais shared quickly. • Nucleus C* retains no “memory” of how it was formed. • C* is almost always formed in an excited state.

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

8. E* mc2 + mc2 mdc2 + mLic2 0.0 mBec2

9. E* mbc2 + mYc2 mac2 + mXc2 0.0 mC*c2 Compound nucleus model

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

11.  Ti* E* mnc2 + mInc2 Tf* 0 mIn-116 c2 mIn-116 c2 Resonances TOF Exp’t

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

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

14. Include spin effects Compound nucleus model