GM Counter and it's applicability in soil studies

1. GM COUNTER AND
IT'S APPLICABILITY IN SOIL STUDIES
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2. ●The Geiger Muller counter is an
instrument used for measuring ionizing
radiations.
●It detects ionization radiations such as
α, β and γ particles using the ionizing
effect produced in Geiger Muller tube.
●In wide and prominent use as a hand-
held survey survey instruments.
INTRODUCTION

3. ●In 1908, the first model of G.M. Counter was
developed by Hans Geiger and Earnest
Rutherford which was only capable of
detecting α- particles.
●In 1928, Geiger and Walther Muller
developed advanced model of sealed G.M.
Tube capable of detecting all kind of
radiations.
●

4. OLD G.M COUNTER
NEWEST AND ADVANCED GM COUNTER

5. CONSTRUCTION
V
1000 – 3000 V R
+ Anode
- Cathode
Gaseous medium
Amplifier and pulse counter
E

6. It mainly consist of a Geiger Muller tube
which is a hollow metallic cylinder and
contains some kind of noble gas.
The gas mixture usually consists of Argon
(90%) at 10 cm of Hg and ethyl alcohol
(10%) at 1 cm of Hg.
The diameter of the cylindrical cathode
varies from 1 cm to 5 cm and it's length
varies from 2 cm to 100 cm depending on
the purpose.

7. ●Now across load resistance there is an electronic
setup as shown in figure.
A metallic electrode which is made up of
tungsten basically connected to a load
resistance.

8. WORKING

9. When an ionizing particles passes through G.M Tube
ionization takes place.
The positive ion and and the electron when created
by some external nuclear particle.
Central electrode acting as an anode and metallic
surface acting as a cathode.
When positive ion and electron is created they will
subjected to extremely high electric field.
There is a battery which is capable of creating a huge
amount of potential difference.

10. Under this potential difference the electron will
experience acceleration towards central electrode
and positive ion moves upwards towards the metallic
surface and is capable of causing secondary , tertiary
and further ionization along it's path.
So, this process will lead to a kind of chain reactions
or an avalanche effect which cause whole lot of
ionization along it's path before reaching the central
electrode so this kind of a phenomena is known as
Avalanche effect or Townsend avalanche.

11. The wire (anode) is surrounded by slow moving
positive ion sheath which reduces the electric field.
As a result of decreased electric field the discharge
stops. The discharge continues to cease till the
positive ions around the wire move away from it.
Since the positive ions take enough time to move
away from the anode so during this period G.M
Counter remains dead.

12. Dead time is the time during which counter fails to
record any other ionizing particle entering the counter.
Positive ions move away from anode towards cathode,
the value of electric field increases and another
discharge takes place.
It is essential that the electric discharge caused by the
first ionizing particle is completely quenched before
the arrival of new particle.

13. COUNT PER SECOND Mainly used for α or β particles
Mainly used for γ or X ray
READ OUT
2 TYPES-

14. CHARACTERISTICS OF G. M.
COUNTER

15. APPLICATIONS OF G.M.COUNTER
For the detection of alpha and beta particles.
To detect radioactive rocks and minerals in the
course of mineral prospecting or as a mineral
collector.
To check for environmental levels of radioactivity.
For fire and police first responders to a analysis for
making an initial determination of radiation risk .

16. APPLICABILITY IN SOIL
STUDIES
●Efficiency of G.M. Counter is low and it's use had
declined markedly since the introduction of
sophisticated Scintillation counters.
● However sample preparation is very simple; no solvent
is used and radiation from sample directly interacts with
the ionization chamber.
●This technique can be readily used on soil providing the
samples are uniformly treated.

17. ●It is used in radioactive tracer technique to evaluate
dynamicity of particular radioactive element in soil
plant system.
●P-32 and P-33 can be used in soil fertility and
phosphorus cycling studies.
●P-32 emitting the β- radiation of high energy can be
readily detected by G.M. Counter.
●The main limitation with the use of P-32 is it's short
half life which limits the duration of crop growth
experiments as compared to P-33 isotopes having
longer half life than P-32

18. DISADVANTAGE
●Because the output pulse of the Geiger Muller tube is always
of the same magnitude regardless of the energy of the
incident radiation,the tube cannot differentiate between
radiation types.
●The inability to measure high radiation rates due to the dead
time of the tube. This is an insensitive period after each
ionization of the gas during which any further incident
radiation will not result in a count, and the indicative rate is
therefore lower than the actual.
There are 2 main limitations of G.M Counter

19. CONCLUSION
Geiger Muller counters are regarded as one of the
world's best radiation detection instruments and is used
widely and prominently as Hand-held radiation survey
instruments .This device is very popular due to it's robust
sensing element and relatively low cost.
G.M Counters are used in numerous fields and it is even
regarded as an indispensable tool for the detection and
measurement of ionizing radiations.

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