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5 Ionization Counters
5.2 Ionization Counter
Although the design of ionization counter can be of varied types, in general, it
comprises two electrodes across which a DC potential difference is maintained.
In between these two electrodes, a mixture of gas is enclosed which provides a
sensitive volume of the detector. These electrodes are usually of plane, parallel or
coaxial cylinders, or of multiwire geometry. Ionizing radiations, interacting with
the gas, transfer energy mainly in the form of excitation or ionization of the gas.
The ionization of gas produces ion-pairs (i.e., electron and positively charged ions).
The respective electrodes of the counter attract these ion-pairs. Each ion-pair when
deposited at the respective electrodes of the counter produces a dc current, which is
measured to find out the number of radiations responsible to produce the ion-pairs.
There are four types of ionization counters as mentioned below and each of them has
their characteristic properties.
1. Ionization Counter
2. Proportional Counter
3. Geiger–Müller Counter
4. Spark Counter
5.3 General Design of an Ionization Chamber
Ionization chamber is made of stainless steel and its outer body is earthed. It comprises two electrodes. The body of the chamber acts as one electrode (normally
earthed), and another one (normally acts as an anode) is enclosed in the chamber
containing argon gas (Fig. 5.1). This central anode carries a positive potential insulated from outer casing by an insulator (y). At the end of the anode wire, there is a
glass bead to stop any discharge of current between the anode and the window (x).
The window is made up of a thin aluminum sheet, which is in contact with the outer
metallic casing of the chamber. The chamber is filled with argon gas at some suitable
pressure (but not more than one atmospheric pressure). The anode is connected
through a variable power source (V ). Potential applied to the anode is measured
across resistance (R).
5.3.1 Current–Voltage Characteristics of the Ionization
Chamber
When a radioactive source is kept near the window, its radiation penetrates through
the window into the active area of the chamber producing ion-pairs. These ion-pairs
have a natural tendency to interact within themselves forming thereby a neutral argon
gas. But in the presence of electrostatic field created between the two electrodes,
5 Ionization Counters
5.2 Ionization Counter
Although the design of ionization counter can be of varied types, in general, it
comprises two electrodes across which a DC potential difference is maintained.
In between these two electrodes, a mixture of gas is enclosed which provides a
sensitive volume of the detector. These electrodes are usually of plane, parallel or
coaxial cylinders, or of multiwire geometry. Ionizing radiations, interacting with
the gas, transfer energy mainly in the form of excitation or ionization of the gas.
The ionization of gas produces ion-pairs (i.e., electron and positively charged ions).
The respective electrodes of the counter attract these ion-pairs. Each ion-pair when
deposited at the respective electrodes of the counter produces a dc current, which is
measured to find out the number of radiations responsible to produce the ion-pairs.
There are four types of ionization counters as mentioned below and each of them has
their characteristic properties.
1. Ionization Counter
2. Proportional Counter
3. Geiger–Müller Counter
4. Spark Counter
5.3 General Design of an Ionization Chamber
Ionization chamber is made of stainless steel and its outer body is earthed. It comprises two electrodes. The body of the chamber acts as one electrode (normally
earthed), and another one (normally acts as an anode) is enclosed in the chamber
containing argon gas (Fig. 5.1). This central anode carries a positive potential insulated from outer casing by an insulator (y). At the end of the anode wire, there is a
glass bead to stop any discharge of current between the anode and the window (x).
The window is made up of a thin aluminum sheet, which is in contact with the outer
metallic casing of the chamber. The chamber is filled with argon gas at some suitable
pressure (but not more than one atmospheric pressure). The anode is connected
through a variable power source (V ). Potential applied to the anode is measured
across resistance (R).
5.3.1 Current–Voltage Characteristics of the Ionization
Chamber
When a radioactive source is kept near the window, its radiation penetrates through
the window into the active area of the chamber producing ion-pairs. These ion-pairs
have a natural tendency to interact within themselves forming thereby a neutral argon
gas. But in the presence of electrostatic field created between the two electrodes,