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DETECTORS
TOPICS TO BE DISCUSSED:
DETECTORS
 CLASSIFICATION OF DETECTORS
 GAS FILLED DETECTOR
 IONIZATION CHAMBER

DETECTOR
DETECTOR IS A DEVICE THAT CONVERTS ENERGY OF
NUCLEAR PARTICLE OR RADIATION INTO USABLE
ELECTRIC SIGNAL.
METHOD OF DETECTION OF RADIOACTIVITY IS BASED ON
INTERACTION OF CHARGED PARTICLES
CLASSIFICATION OF DETECTORS
DETECTORS
GAS FILLED
SEMICONDUCTOR
SCINTILLATOR
DETECTOR
ELECTRICAL
SCINTILLATI
ON
OPTICAL
IONIZATION
CHAMBER
GM COUNTER
PROPORTIONAL
GAS FILLED DETECTORS
PRINCIPLE OF GAS
FILLED DETECTORS:
IONIZATION CHAMBER, PROPORTIONAL
COUNTER AND GM COUNTER ARE DIFFERENT
TYPES OF GAS FILLED DETECTORS. THESE ARE
BASED ON THE PRINCIPLE THAT CHARGED SUB
ATOMIC PARTICLES CAN IONIZE A GAS. THE
NUMBER OF IONS FORMED GIVES INFORMATION
ABOUT NATURE OF INCIDENT PARTICLES AS
WELL AS THEIR ENERGY.
THE PASSAGE OF NUCLEAR RADIATION THROUGH GAS
DETECTOR PRODUCES A PULSE SIGNAL WHICH CAN BE
PROCESSED FURTHER FOR COUNTING. THE OUTPUT
PULSE HEIGHT AT ANODE WILL DEPEND
ON
FOLLOWING FACTORS……….
External voltage applied
 Initial ionizing event-that is weather pulse has
been initiated by passage of α particles or β
particles.
 This behavior has been depicted in the following
fig, where graph between the output(or pulse
height as a function of applied voltage has been
shown.
 Curve (a), corresponds to large initial ionizing
event and curve (b),to smaller ionizing event.

REGION1: APPLIED VOLTAGE IS
SMALL SO THAT RECOMBINATION TAKES
PLACE.
REGION
2: VOLTAGE IS ENOUGH
HIGH SO THAT NEGLIGIBLE
RECOMBINATION TAKE PLACE
CALLED IONIZATION REGION.
REGION3: ELECTRONS
APPROACHING CENTRAL WIRE GAIN
SUFFICIENT ENERGY SO THAT HAVE
COLLISIONS WITH GAS MOLECULES
CAN TAKE PLACE. NO OF IONS
PRODUCED ,AS ION MOVE TOWARDS
CENTRAL WIRE IS CALLED
MULTIPLICATION FACTOR.
REGION4: IF VOLTAGE IS
INCREASED FURTHER PULSE
HEIGHT IS NO LONGER
PROPOTIONAL TO INITIAL
IONIZATION CALLED REGION
OF LIMITED PROPOTIONALITY
REGION 5: FOR MORE HIGHER
VOLTAGE IN WHICH PULSE
HEIGHT
IS
LARGER
INDEPENDENT OF INITIAL IONS
CALLE GEIGER REGION.
REGION6: AT END OF GEIGER
REGION THERE IS A CONTINOUS
DISCHARGE ,ITS RTEALLY NOT
CONTINOUS BUT CONSIST OF
MULTIPLE PULSES.
1.
IONIZATION CHAMBER
DRAWBACKS:
after detection of first particle detector has to be
wait for miliseconds,before it is ready to detect
the next particle.
 it is not useful for detection of electron because of
their low primary ionization.

USES:
ionization chamber have been used to study
alpha particles, protons and nuclei of lighter
elements.
 for the detection of neutron, chamber is filled
with boron trifluroide.

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