G M COUNTER

USE: To measure the intensity of the Radioactive radiations.

PRINCIPLE: Ionisation produced in the gas by nuclear radiations .

CONSTRUCTION: 
* A metal tube with glass envelope (C) act as cathode.
                                  
*A fine tungsten wire (W) along the axis of the tube, act as anode.
                                 
* GM tube insulated from the wire is filled with an inert gas like argon at a low pressure.
                                  
* The radiations enter through a window (E) made of thin mica sheet.



*About 1000 volt is applied through a high resistance R (100 M ohm)
                                    

WORKING:           

* Due to primary ionisations few ions produced are  accelerated by high potential difference .  
                                   
* These ions/electrons cause further ionisation and due to collisions, avalanche of electrons are produced.
                                    
* These electrons reaching the anode produces a current pulse.
                                   
* A high potential difference developed across R is amplified and operates an electronic counter. 


* The counts in the counter is directly proportional to the Intensity of Ionising radiations.


* Ionisation of the gas does not depend on type of Incident radiations.


* Wilson's Cloud Chamber ,a particle detector records the visual observations of the tracks of charged particles.