5. oIt is a ion collection based detector which
is used to Detect the nuclear particles or
radiations.
oIt is classified in gaseous state detectors
Introduction
7. 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.
8. 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
9.
10. Operation
E =
𝑉
𝑟 ln(
𝑏
𝑎
)
Where:-
V = applied potential difference
b = radii of the cylinder
a = radii of an axial wire
r = distance from the central wire
11. 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.
12. In this multiplication or gas amplification, the number of
ions increases exponentially.this process is cumulative and is
called avalanche.
14. The value of gas multiplication factor ‘M’ is give by 103 in
this region.
M=
𝑛
(1−𝑛𝑝)
Here
n=number of secondary electrons produced by the primary eletrons.
p=the probability of production of photoelectrons.
15. The shape of the voltage pulse does not depend on the
track of the primary ions.
16. 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.
17. 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.
