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8/14/2019 Section 18.4 Detection of Radiation
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Section 18.4Section 18.4
Detection of radiationDetection of radiation
Photographic filmPhotographic film
Geiger-Muller counterGeiger-Muller counter
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Detection of radiation
seen
heard
smelt tasted
touched
Radiation cannot be
1. Photographic film
2. Diffusion cloud
chamber
3. Geiger-Muller counter
Methods of detections
18.4 Detection of radiation (SB p. 27)
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Photographic film
Expt. 18E
Blackening of
photographic film
A set-up demonstrates
the blackening effect of
radiation on aphotographic film
sealed
photographic film
key
lifting
tool
sealedradiumsource
18.4 Detection of radiation (SB p. 27)
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Photographic film
penetratesthe
wrapping of film
filmblackened
leaving shape of key on
film
18.4 Detection of radiation (SB p. 28)
cannot penetrate
the metal key
radiation
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consists of two components:
(1) GM tube
(2) scaler
(total no. of counts over a time interval)
orratemeter(no. of counts/second)
Geiger-Muller(GM) counter
Geiger-Muller counter
can measure the amount of radiation
18.4 Detection of radiation (SB p. 28)
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argon gasmetal wire as
anode (+)
thin mica
window
radiationinsulator
inner wall as
cathode ()
GM tube a metal tube filled with argon gas at low pressure
An electric field is set up
inside by the d.c. voltage
By the action of electric field, the
electron moves towards the anode
By the action of electric field,
the positive ion movestowards the cathode
Electric pulses
produced &
recorded
ionized argon gas
The argon gas is ionized by radiation
Working principle of GM counter
18.4 Detection of radiation (SB p. 29)
radiation enters
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no. of counts recorded no. of disintegration of /
weak ionizing powerof efficiency of detecting much lower
advantage: only measures intensityof radiation
18.4 Detection of radiation (SB p. 29)
Detecting of , ,
Advantage / disadvantage
Use of GM counter
disadvantage: cannot distinguish types of radiation
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Class Practice 5:Class Practice 5:A student wants to measure radiation in the following situations.
Match the suitable detector with each of the following situations.
Situation Detector
(a) To test the radiation exposureover one week.
(b) To locate the position of a
building with minimum
radiation intensity.
(c) To count the number of -particles emitted by asource in 5 minutes.
GM tube connected to a scaler
GM tube connected to a ratemeter
Photographic filmAns
wer
18.4 Detection of radiation (SB p. 29)
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Radiation intake from food
Expt 18FRadiation
intake from
food
Somefood contains
radioactive substances content is low
but accumulate in bodieslong term effect
18.4 Detection of radiation (SB p. 30)
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To section 18.5
http://e-ch18_05.ppt/http://e-ch18_05.ppt/Recommended