Chapter 4
Particle scattering
The interaction of fast charged particles with matter provides the
basic physical mechanism underlying most applications of charged
particle beam instruments. In this interaction, an incident particle
strikes a target, transfering momentum and energy. The incident
particle is completely characterized by its rest mass, charge, momentum, and spin polarization. The target can consist of bulk
material (solid, liquid, or vapor), a single atom, a molecule, or a
second particle (composite or pointlike). The interaction can be
governed by the strong, weak, Coulomb, or gravitational forces.
The gravitational force is too weak to be important for charged
particles on the laboratory scale of dimensions. However the classical Kepler problem is formally identical to Coulomb scattering
between two individual charged particles via the inverse square
dependence of the instantaneous force on the separation. In all
cases, the interaction can be used to probe the physical or chemical properties of the target.
In some cases where the rest mass of the incident particle is much
smaller than the target particle, the incident particle transfers negligible energy to the target. Such an event is known as elastic
scattering. An example is the angular deflection of a fast electron
by the screened Coulomb potential of an atomic nucleus. This
provides the basic contrast mechanism of a transmission electron
microscope. In elastic scattering, the phase relationship of the in233
Particle scattering
The interaction of fast charged particles with matter provides the
basic physical mechanism underlying most applications of charged
particle beam instruments. In this interaction, an incident particle
strikes a target, transfering momentum and energy. The incident
particle is completely characterized by its rest mass, charge, momentum, and spin polarization. The target can consist of bulk
material (solid, liquid, or vapor), a single atom, a molecule, or a
second particle (composite or pointlike). The interaction can be
governed by the strong, weak, Coulomb, or gravitational forces.
The gravitational force is too weak to be important for charged
particles on the laboratory scale of dimensions. However the classical Kepler problem is formally identical to Coulomb scattering
between two individual charged particles via the inverse square
dependence of the instantaneous force on the separation. In all
cases, the interaction can be used to probe the physical or chemical properties of the target.
In some cases where the rest mass of the incident particle is much
smaller than the target particle, the incident particle transfers negligible energy to the target. Such an event is known as elastic
scattering. An example is the angular deflection of a fast electron
by the screened Coulomb potential of an atomic nucleus. This
provides the basic contrast mechanism of a transmission electron
microscope. In elastic scattering, the phase relationship of the in233