How Geiger Mueller Counter Work

A Geiger Mueller Counter is a device used for the detection and measurement of all

types of radiation: alpha, beta and gamma radiation. The counter works on the "principle

of gas multiplication". Ionization in the gas is caused by the entry of photon or a

particulate radiation. The ions are attracted to their appropriate electrode (i.e. cation to

cathode, anion to anode) and thy gain sufficient energy to eject electrons from the gas

atoms as they pass through the gas. This causes the atoms to ionize. Therefore

electrons are produced continuously by this process and rapid gas multiplication takes

place (especially in the central electrode because of its strong electric field strength).

The effect of "gas multiplication" is that more than one million electrons are collected by

the central electrode for every ion produced in the primary absorption process. Theses

"electron avalanches" create electric pulses which then can be amplified electronically

and counted by a meter to calculate the number of initial ionization events. Therefore a

Geiger counter is able to detect low-energy radiation because even one ionized particle

produces a full pulse on the central wire.

Application

1. Particle detection

2. Gamma and X-ray detection

3. Neutron detection

4. Gamma measurement—personnel protection and process control

Advantages

1. Geiger counters are even more useful because they can be fine-tuned to the type

of radiation that is expected.

2. Can detect and measure all types of radiation.

Disadvantages

1. Inability to measure high radiation rates.

2. Geiger-Muller tube cannot differentiate between radiation types.

Price: US$85.00

How Ionization chamber work

When ionising radiation interacts with air, it produces ions (typically electrons and

positively charged atoms from which they arrived). In the presence of charge, the

positive particles will migrate towards a negative terminal and vice versa.

Ionisation chambers utilise this principle. All types contain a positive and negative

terminal, separated by a gas (typically air). As ions reach their respective terminals, they

produce a current which is detectable by an electrometer. The charge used within an

ionisation chamber (100-400 V) is sufficient to pull ions towards the terminals, but not

excessive enough to accelerate them and create further ionisations (see Geiger Muller

Counters ).

Ionisation chambers need to have correction factors applied for different beam energies.

They are highly sensitive (down to individual ionisations) which makes them useful in a

variety of applications.

Application

1. Nuclear industry

2. Smoke detectors

3. Medical radiation measurement

Advantages

1. Simple and easy to build.

2. Good in measuring high levels of gamma radiation.

Disadvantages

1. Electrical current produced is extremely weak, and must be amplified with

sophisticated electronic circuitry.

2. The output current tends to drift with time, and the system must be frequently re-

zeroed.

Price : US$3299.00

How Proportional counter work

The proportional counter is a type of gaseous ionization detector device used to

count particles of ionizing radiation that mean ability to measure the energy of incident

radiation and it is widely used where discrimination between radiation types is required,

such as between alpha and beta particles.

A proportional counter uses a combination of the mechanisms of a Geiger-Muller

tube and an ionization chamber that operates in an intermediate voltage region between

these. Considering a gas-filled chamber with a wire anode, if the field strength

everywhere in the volume is below a critical value, Townsend avalanches do not occur

at all, and the detector operates as an ionization chamber. If the applied voltage is too

high, complete ionisation of the fill gas occurs with almost each ion pair and the detector

operates as a Geiger-Müller counter, with the consequent loss of incident particle

energy information. The accompanying plot shows the proportional operating region for

a co-axial cylinder arrangement

In a proportional counter the fill gas of the chamber is an inert gas which is ionised by

incident radiation, and a quench gas to ensure each pulse discharge terminates; a

common mixture is 90% argon, 10% methane, known as P-10. An ionizing particle

entering the gas collides with a molecule of the inert gas and ionises it to produce an

electron and a positively charged atom, commonly known as an "ion pair". As the

charged particle travels through the chamber it leaves a trail of ion pairs along its

trajectory, the number of which is proportional to the energy of the particle if it is fully

stopped within the gas. Typically a 1 MeV stopped particle will create about 30,000 ion

pairs.

Applications

i. Spectroscopy .

ii. Photon detection.

iii. Radioactive contamination detector.

Advantages

1. They are versatile in that they can be used for a variety of different applications.

2. Proportional counters can detect a variety of radiations.

3. They can also distinguish among radiation types.

Disadvantages

1. Proportional counters require a stable high voltage supply.

2. In general, these detectors are more expensive than GM countersiii.

Price : US$1,200