Introduction to GM Counter

1. GM Counter
Presented by: Ehsan Yousaf
Roll no: SSR-18-12 (Replica)

2. Contents:
Introduction
History
GM Counter Figure
Principle
Diagram
Experiment
Graph

3. Introduction
• The Geiger Muller Counter is an
instrument used for measuring ionizing
radiation.
• It detects ionization radiations such as α-
particles, β-particles and ϒ rays using
the ionization effect produced in a GM
Counter.

4. History
• The original detection principle was discovered in
1908.
• In 1908, The first model of GM counter was
developed by Hans Gieger and Ernest Rutherford
which was only capable of detecting alpha particles.
• In 1928, Geiger and Walther Muller developed
advanced model of GM counter consisting of sealed
GM Tube capable of detecting all kinds of radiation.
• With the development of the GM tube in 1928 that
the GM counter became a practical Instrument.

5. GM Counter

6. Principle
• A GM counter consists of Geiger-Muller tube, the
sensing element which detects radiation.
• GM Tube is filled with an inert gas such as
Helium, Neon or Argon at low pressure to which
high voltage is applied.
• GM Tube briefly conducts electrical charge when
a particle or photon of incident radiation makes
the gas conductive by ionization

7. Diagram:

8. Diagram:

9. Principle of Operation:
When a single gamma or beta ray entering
the tube, a small amount of ionization is
produced.
The center electrode which is at high positive
potential attracts the electrons and gives
them energy to produce further ionization
until the whole volume contains ion pairs.

10. The electrons are rapidly collected.
The voltage on the center electrode drops
and the slow positive ions go to the outer
wall.
After 400 sec (Dead time) the tube is
ready to repeat the process.

11. Types of Radiation Detectors:
GM Counter
Scintillation Counter
Proportional Counter
Multi channel Analyzer System
Ionization chamber

12. Experiment:
To determine the range of β-particle

13. 8. As with GM tube, working voltage is chosen so that saturation
ionization current is achieved, for then the sensitivity is
independent of applied voltage.
9. The graph gives the characteristics of ionization chamber.
10. Measure the distance d between source and gauze .
11. Record the ionization current I.
12. Plot a graph between distance d and ionization current.
13. Find range of beta particle from graph.
Precautions:
 Distance between source and counter should remain fixed.
 Handle the radioactive source by lifting tool.
 All connections should be neat and tight to avoid spurious
counts.
 After switching on the counter wait for 5 min for its warm up.

14. Graph: