4 Gaseous Detectors
93
of major directions of detector design and performance follows in Sect. 4.3: Singlewire tubes (Sect. 4.3.1), Multi-Wire-Proportional Chambers (Sect. 4.3.2), Drift
Chambers (Sect. 4.3.3), Resistive Plate Chambers (Sect. 4.3.4) and Micropattern
Devices (Sect. 4.3.5).
4.2 Basic Processes
As most processes depend on the velocity of a particle, we shall often state
numerical values for minimum ionizing particles (mip), i.e. for γ = 3 − 4.
4.2.1 Gas Ionization by Charged Particles
The passage of charged particles through a gas is signaled by the production
of electron/ion pairs along its path. The electrons are attracted by electrodes on
positive potential, in the vicinity of which they are usually amplified in a avalanche
process. We give a short summary of the various aspects of the ionization processes,
following to some extent [19].
4.2.1.1 Primary Clusters
The ionizing collisions of the particle are occurring randomly with a mean distance
λ, related to the ionization cross-section per electron σ I and the electron density N e
of the gas:
1/λ = N e σ I .
(4.1)
The number k of ionizing collisions on a path length L thus follows a Poisson
distribution with mean L/λ:
P (k|L, λ) =
(L/λ)
k /k!
exp (−L/λ) .
(4.2)
The probability to have no ionization in L is
P (0|L, λ) = exp (−L/λ) .
(4.3)
This relation is used to determine λ and defines the inefficiency of a counter
measuring a track length L, if it is sensitive to a single primary electron.
93
of major directions of detector design and performance follows in Sect. 4.3: Singlewire tubes (Sect. 4.3.1), Multi-Wire-Proportional Chambers (Sect. 4.3.2), Drift
Chambers (Sect. 4.3.3), Resistive Plate Chambers (Sect. 4.3.4) and Micropattern
Devices (Sect. 4.3.5).
4.2 Basic Processes
As most processes depend on the velocity of a particle, we shall often state
numerical values for minimum ionizing particles (mip), i.e. for γ = 3 − 4.
4.2.1 Gas Ionization by Charged Particles
The passage of charged particles through a gas is signaled by the production
of electron/ion pairs along its path. The electrons are attracted by electrodes on
positive potential, in the vicinity of which they are usually amplified in a avalanche
process. We give a short summary of the various aspects of the ionization processes,
following to some extent [19].
4.2.1.1 Primary Clusters
The ionizing collisions of the particle are occurring randomly with a mean distance
λ, related to the ionization cross-section per electron σ I and the electron density N e
of the gas:
1/λ = N e σ I .
(4.1)
The number k of ionizing collisions on a path length L thus follows a Poisson
distribution with mean L/λ:
P (k|L, λ) =
(L/λ)
k /k!
exp (−L/λ) .
(4.2)
The probability to have no ionization in L is
P (0|L, λ) = exp (−L/λ) .
(4.3)
This relation is used to determine λ and defines the inefficiency of a counter
measuring a track length L, if it is sensitive to a single primary electron.