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.
                    
                                     

J.J.THOMSON METHOD TO FIND e/m :

ENLARGE BY CLICKING

LONG SOLENOID

MAGNETIC INDUCTION DUE TO A LONG SOLENOID CARRYING CURRENT:

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CYCLOTRON

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CIRCULAR COIL

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MILLIKAN OIL DROP

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ROBERT MILLIKAN,MARCH 22,1868

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YOUNG'S DOUBLE SLIT

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thomas young,june 13,1773

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EFFECT OF FREQUENCY

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GRAPH,2

VAN DE GRAAFF

VAN DE GRAAFF GENERATOR:

PRINCIPLE: 

  *IT WORKS ON THE PRINCIPLE OF ELECTROSTATIC INDUCTION AND ACTION OF POINTS.

CONSTRUCTION:

 * 'A' BE THE HOLLOW METALLIC SPHERE MOUNTED ON INSULATING PILLARS.

 * 'B' AND 'C' BE THE TWO PULLEYS.'B' IS MOUNTED AT THE CENTRE OF THE SPHERE AND 'C' IS MOUNTED NEAR THE BOTTOM.


 * PULLEY 'C' IS DRIVEN BY AN ELECTRIC MOTOR.


 *A SILK BELT MOVES OVER THE PULLEYS.

 *'D' AND 'E' BE THE TWO COMB SHAPED CONDUCTORS HAVING SHARP NEEDLES WHICH ARE MOUNTED NEAR THE PULLEYS.


 *COMB 'D' IS GIVEN A POSITIVE POTENTIAL (10^4 V) BY A POWER SUPPLY.


 *COMB 'E' IS CONNECTED TO THE INNER SIDE OF THE HOLLOW SPHERE.

WORKING:

 *SINCE HIGH ELECTRIC FIELD IS AT 'D' AIR GETS IONISED DUE TO ACTION OF POINTS.

 *NOW THE NEEDLE ATTRACTS NEGATIVE CHARGES AND REPELS POSITIVE CHARGES TOWARDS THE BELT.

 *THE POSITIVE CHARGES STICK TO THE BELT, MOVES UP AND REACHES 'E'.


 *'E' ACQUIRES NEGATIVE CHARGES DUE TO ELECTROSTATIC INDUCTION AND SPHERE ACQUIRES POSITIVE CHARGES  WHICH ARE DISTRIBUTED ON ITS OUTER SURFACE.

  *THE HIGH ELECTRIC FIELD AT 'E' IONISES THE AIR AND HENCE NEGATIVE CHARGES ARE REPELLED TOWARDS THE BELT.


 *DUE TO THIS THE POSITIVE CHARGES ARE NEUTRALISED BEFORE THE BELT MOVES OVER THE PULLEY.

 *SO THE DESCENDING BELT IS LEFT UNCHARGED.


 *THE POTENTIAL OF THE  SPHERE KEEPS ON INCREASING AND REACHES A MAXIMUM OR LIMITING VALUE.


 *AFTER THIS STAGE LEAKEGE OF CHARGES OCCUR DUE TO IONISATION OF AIR.

ROBERT J.VAN DE GRAAFF

 *THIS LEAKAGE CAN BE REDUCED BY ENCLOSING  THE MACHINE IN A GAS FILLED STEEL CHAMBER AT A VERY HIGH PRESSURE.

USES:

 *USED TO PRODUCE LARGE ELECTROSTATIC POTENTIAL DIFFERENCE UP TO 10^7  V.

 *THIS HIGH VOLTAGE IS USED TO ACCELERATE THE POSITIVE IONS (PROTONS,DEUTRONS ) FOR NUCLEAR FISSION PROCESS.