5 Interactions of Beams with Surroundings
185
While electromagnetic interactions can be described in one coherent theory
(QED), the same does not apply to hadronic nuclear interactions.
The development of hadron initiated showers is determined both by atomic
processes (e.g. ionization, multiple Coulomb Scattering, etc.), which take place very
frequently, as well as relatively rare nuclear interactions (both elastic and nonelastic). Electromagnetic showers are determined by the same atomic processes plus
additional ones (e.g., Bremsstrahlung, pair production, Compton scattering, etc.)
which are specific for electrons, positrons or photons. Nuclear interactions coming
from the electromagnetic component usually play a minor role, and whenever the
interest is not in the small fraction of hadrons produced by electromagnetic particles
they can be safely neglected.
Concerning particle production, energetic (shower) particles are concentrated
mainly around the primary beam axis, regardless of their identity. Their ionization
as well as the electromagnetic cascades define the core of the energy deposition
distribution. At the same time, neutrons (since these are the only neutral hadrons
with a long enough lifetime) will dominate at energies where charged particle
ranges become shorter than the respective interaction length. In this sense, the
energy deposition associated with low energy neutron interactions constitute the
peripheral tails of the energy deposition distribution. Most of the interactions are
due to particles (mainly neutrons) of moderate energy.
Pions can be only produced by shower particle interactions, so that they are often
considered as the real indicator of a high energy cascade. Neutrons, and to a lesser
extent protons, are copiously produced also in the final stages of nuclear interactions
(e.g., evaporation) down to projectile energies that are comparable to their nuclear
binding energy.
As previously mentioned, to focus on the relevant processes one usually distinguishes between continuous and discrete (or explicit) processes. This distinction
reflects a real physical distinction, between processes which occur very frequently
with mean free paths much shorter than particle ranges in matter, and others
that, however, are often the dominating ones in determining the shower development.
The most important discrete processes are:
• inelastic nuclear interaction;
• decay;
• elastic nuclear interaction;
• delta-ray production;
• bremsstrahlung;
• annihilation;
• photoelectric effect;
• Compton scattering;
• pair production;
• coherent (Rayleigh) scattering.
In addition to these processes, nuclear interactions with a much lower rate can
occur also for photons (as well as with a reduced rate of about 1/137 for electrons
185
While electromagnetic interactions can be described in one coherent theory
(QED), the same does not apply to hadronic nuclear interactions.
The development of hadron initiated showers is determined both by atomic
processes (e.g. ionization, multiple Coulomb Scattering, etc.), which take place very
frequently, as well as relatively rare nuclear interactions (both elastic and nonelastic). Electromagnetic showers are determined by the same atomic processes plus
additional ones (e.g., Bremsstrahlung, pair production, Compton scattering, etc.)
which are specific for electrons, positrons or photons. Nuclear interactions coming
from the electromagnetic component usually play a minor role, and whenever the
interest is not in the small fraction of hadrons produced by electromagnetic particles
they can be safely neglected.
Concerning particle production, energetic (shower) particles are concentrated
mainly around the primary beam axis, regardless of their identity. Their ionization
as well as the electromagnetic cascades define the core of the energy deposition
distribution. At the same time, neutrons (since these are the only neutral hadrons
with a long enough lifetime) will dominate at energies where charged particle
ranges become shorter than the respective interaction length. In this sense, the
energy deposition associated with low energy neutron interactions constitute the
peripheral tails of the energy deposition distribution. Most of the interactions are
due to particles (mainly neutrons) of moderate energy.
Pions can be only produced by shower particle interactions, so that they are often
considered as the real indicator of a high energy cascade. Neutrons, and to a lesser
extent protons, are copiously produced also in the final stages of nuclear interactions
(e.g., evaporation) down to projectile energies that are comparable to their nuclear
binding energy.
As previously mentioned, to focus on the relevant processes one usually distinguishes between continuous and discrete (or explicit) processes. This distinction
reflects a real physical distinction, between processes which occur very frequently
with mean free paths much shorter than particle ranges in matter, and others
that, however, are often the dominating ones in determining the shower development.
The most important discrete processes are:
• inelastic nuclear interaction;
• decay;
• elastic nuclear interaction;
• delta-ray production;
• bremsstrahlung;
• annihilation;
• photoelectric effect;
• Compton scattering;
• pair production;
• coherent (Rayleigh) scattering.
In addition to these processes, nuclear interactions with a much lower rate can
occur also for photons (as well as with a reduced rate of about 1/137 for electrons