Special Nuclear Reactions: Basic Concepts

Special Nuclear Reactions

1. Neutron Induced Fission

2. Fusion

3. Photonuclear Reactions

4. Heavy Ion Reactions

Neutron Induced Fission

• A neutron is captured by heavy nuclide to form a compound nucleus

• Compound nucleus then splits into two smaller fragments and emits two or three free neutrons along with 200 MeV of energy

• For low-mass nuclides, binding force >> Coulomb force, fission is not feasible

• For Heavy nuclides, binding force ≈ Coulomb force, addition of neutron shift the balance in favor of repulsive force

• Neutron provides some internal excitation energy that deforms the nucleus into a transition state

• Severe deformations, split the nucleus into two fragments 

The fission process involves the deformation of a nucleus through a series of shapes like those shown in figure below

Low energy neutron: asymmetric  fission

High energy neutron: symmetric  fission

Fusion

• Non spontaneous on earth

• Spontaneous in sun and star

• Threshold reactions ( charged particle reaction)

• Fusion has several advantages over fission as a source of energy

• Unlimited deuterium from oceans

• The products of d-d and d-t fusion reactions are not radioactive

• No significant waste disposal problems

   

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These reactions take places using accelerators are not self-sustaining reactions, the require the continual input of energy to continue.

Photonuclear Reactions

• Induced by electro-magnetic radiation

• Threshold reactions

• Imparted low energy on target,   emission ofone or two nucleons, (γ, n), (γ, 2n), (γ, p)

• Cross section usually on the order of millibarns

• Excitation functions  show giant resonance

Heavy Ions Reactions

• Mass > ⁴He

• ¹²C⁶⁺, ⁴⁰Ar⁸⁺, ⁸⁴Kr³⁰⁺, ²³⁵U⁵⁰⁺

• High charge, formidable Columb barrier

• Deep inelastic reaction