Proportional counter

PROPORTIONALCOUTER

OBJECTIVESIntroductionconstructionPrincipleOperationWorkingUsesAdvantageDisadvantage

PROPORTIONAL COUNTER

Classification of detectors

o It is a ion collection based detector which is used to Detect the nuclear particles or radiations.

o It is classified in gaseous state detectors

Introduction

CONSTRUCTION

Thin metalic wire strip

o It contains cylinder metallic tube filled with argon and methane gas.

o The ratio of argon and methane gas is 9:1 at one atmospheric pressure .

o Metallic wire (tungsten) act as a anode.o Metallic tube act as a cathode.o The wire is connected to pulse amplifire.

When a particle of low specific ionization passes through an ionisation chamber the pulse produced is too small to be detected.

When applied voltage is increased in chamber is increased it start works in proportinal region.

PRINCIPLE

Operation

E

Where:- V = applied potential difference b = radii of the cylinder a = radii of an axial wire r = distance from the central wire

When a charged particle or radiation such as ᾳ, ᵦ-particle or ϒ-ray photon enters an ionisation chamber, ionisation of gas take place resulting in an ion pair formation.

Positive ion chamber.Electron central

wire.

In this multiplication or gas amplification, the number of ions increases exponentially.this process is cumulative and is called avalanche.

Dependency of avalanche

Radius of anode wire.Radius of tube.Applied voltage.Nature of gas.

The value of gas multiplication factor ‘M’ is give by in this region.

M Here n=number of secondary electrons produced by the primary eletrons. p=the probability of production of photoelectrons.

The shape of the voltage pulse does not depend on the track of the primary ions.

Uses

The proportional counter permits both the counting and energy determination of particles even of very low energy.

It can be used as a spectrometer.They are also used for detection of neutrons,

fission fragments etc.Counting ᾳ-particle in the presence of ᵦ-

particle and ϒ-rays.

Disadvantage

This counter is that the amplification factor depends on the applied voltage.

The applied voltage must be maintained constant within the narrow limit because a slight change in voltage changes the gas amplification.

Harish Kumawat 15CS15

Harsh Bansal 15CS16

Harshit gupta 15CS17

Hemant Khorwal 15CS18

Hemraj Saini 15Cs19

Himani Sharma 15CS20

Hitesh Runthala 15CS21

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