Introduction

Much of our knowledge of nuclear physics comes from the study of nuclear reactions. We consider nuclear reactions resulting from a collision between two nuclei. As a result, we can have a rearrangement of the nucleons so that the final state differs from the intial state. We consider mainly final states in which there are one or two nuclei.

Nuclear reactions are thus a transition between an initial state and a final state.

Binary reactions with a two-body final state may generally be denoted as

where a is a projectile, A a target nucleus, b an ejectile and B a residual nucleus. This is often represented as

Many important reactions are of this type.

Some examples of reactions (note also the notation) are

Elastic scattering

-- no change in the internal energy of the constituents.

Inelastic scattering

-- there is a change in the internal energy of the , and hence in the energy of the outgoing alpha (hence the prime).

Pickup reaction

. A proton is ``picked up'' from the target nucleus. This is a typical rearrangement collision.

The final states that are accessible in a collision are governed by the conservation laws. For the reaction above, conservation of baryon number and charge results in and . As long as we are not dealing with beta decays, the number of protons and neutrons in a reaction are separately conserved.