What is a Geiger Muller?
The Geiger-Müller tube or the G-M tube is the sensor element of the Geiger counter instrument used for the detection of ionizing radiation.Hans Geiger developed the device in 1908.In 1928, Geiger and Walther Muller improved the GEIGER MULLER 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 OF GEIGER MULLER TUBE
- 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 OF GEIGER MULLER COUNTER
- 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-tri fluride .
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
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