development of micro-pattern gaseous detectors – gem - LMU

Chapter 1
Interactions of Charged Heavy Particle
and Photons in Matter
This chapter deals with the physics inside a gaseous detector. The interaction of charged heavy 1
particle in matter and the derivation of their specific energy loss according to Bethe-Bloch is presented
before the primary interactions of photons with matter. Ch. 1.2 documents the behavior of
liberated charges in a gas volume with or without an applied electric field leading to the principle of
gas amplification.
1.1 Primary Processes in Gaseous Detectors
[Grup 08, Ch.1], [Bieb 08, Ch.2], [PDG 10], [Leo 94], [Klei 92]
When a particle interacts with matter, the physical reaction can be abstracted to an interaction of a
(virtual) photon with an atom. This is called the Photo-Absorption-Ionization-Model and will be illuminated
in the following to guide to the important primary processes of particle in gaseous detectors.
1.1.1 Ionization and Excitation
Model of Photo-Ionization and -Absorption
The interaction of heavy charged particle with matter is of electromagnetic nature and therefore mediated
by photons.
Figure 1.1: Photo-ionization-absorption model
In the so called photo-ionization-absorption model one treats the electromagnetic interaction, that
is the energy loss, of a particle with charge q = Z · e, mass m and velocity v = β · c like the
1 heavy relative to an electron
7