GEIGER MULLER COUNTER

BY:

Samiksha Dhamarikar

INTRODUCTION

• Hans Geiger developed the device in 1908  • In 1928, Geiger and Walther Muller improved the

counter so that it could detect more types of ionizing radiation.

•  Particle detector that measures ionizing radiation

• The particles are usually beta and gamma rays, but certain models can also detect alpha particles.

CONSTRUCTION

• The Geiger-Muller tube, which is a cylindrical glass chamber filled with a mixture of an inert gas (e.g. Neon at nearly 0.1 atm) and halogen.

• Two electrodes anode and cathode coated with graphite.

• Anode is represented by wire in the centre while cathode forms the lateral area.

• One end of the cylinder from which radiation enters is sealed by Mica window.

• A high voltage supply for the tube.

• A scaler to record number of particles detected by the tube

• The source consists of any radioactive material.

WORKING

• As the radiation from the radioactive source enters the gieger-muller tube through the mica tube, it ionizes the gas inside it.

• The gas transforms into positively charged ions and electrons.

• Eventually electrons move towards anode and positively charged particles collide with the remaining inert gas to form more ions, by avalanche effect.

• This creates a short, intense pulse of current between anode and cathode.

• This current is collected, amplified, counted and displayed.

• The halogens present in the mixture prevent the emission of secondary ions by quenching.

• Most tubes detect beta and gamma radiation of about 2.5 MeV.

• To detect alpha particles mica window is used.

• Most G. M. Counters cannot detect neutrons as they do not ionize.

• However, neutron sensitive tube can be designed by coating the inner surface of the tube with boron or boron-trifluride .

SOURCES

Following radioactive materials are used to detect various radiations:

• Alpha source-

Pu-239 or Am-241• Beta source-

Sr-90 • Gamma source-

Co-60 with beta ray filter.

GRAPH BETWEEN COUNT AND APPLIED VOLTAGE

ADVANTAGES

• They are inexpensive.

• They are durable and easily portable.

• They can detect all types of radiation.

DISADVANTAGES

• They cannot differentiate which type of radiation is being detected.

• They cannot be used to determine the exact energy of detected radiation.

• They have low efficiency.

REFERENCES

• Wikipedia

THANK YOU