Section 18.4 Detection Of Radiation

Section 18.4 Detection of radiation • Photographic film • Geiger-Muller counter

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18.4 Detection of radiation (SB p. 27)

Detection of radiation Radiation cannot be • seen • heard • smelt • tasted • touched

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Methods of detections 1. Photographic film 2. Diffusion cloud chamber 3. Geiger-Muller counter

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18.4 Detection of radiation (SB p. 27)

Photographic film Expt. 18E Blackening of photographic film

A set-up demonstrates the blackening effect of radiation on a photographic film

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sealed radium source lifting tool sealed photographic film

key

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18.4 Detection of radiation (SB p. 28)

Photographic film radiation penetrates the wrapping of film

cannot penetrate the metal key

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film blackened

leaving shape of key on film 4

18.4 Detection of radiation (SB p. 28)

Geiger-Muller counter Geiger-Muller (GM) counter — can measure the amount of radiation — consists of two components: (1) GM tube (2) scaler (total no. of counts over a time interval) or ratemeter (no. of counts/second) © Manhattan Press (H.K.) Ltd.

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18.4 Detection of radiation (SB p. 29)

Working principle of GM counter GM tube —a metal tube filled with argon gas at low pressure radiation enters radiation

thin mica window

Electric pulses ionized argon The argon gasgas is ionized by radiationproduced & insulator recorded

By the action of electric field, By the action of electric field, the the positive ion moves electron moves towards the anode towards the cathode metal wire as inner wall as argon gas anode (+) cathode (−)

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An electric field is set up inside by the d.c. voltage

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18.4 Detection of radiation (SB p. 29)

Use of GM counter

Detecting of α , β ,  • no. of counts recorded ∝ no. of disintegration of α / β • weak ionizing power of 

→ efficiency of detecting much lower Advantage / disadvantage

advantage: only measures intensity of radiation disadvantage: cannot distinguish types of radiation © Manhattan Press (H.K.) Ltd.

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18.4 Detection of radiation (SB p. 29)

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 exposure over one week. (b) To locate the position of a building with minimum radiation intensity. (c) To count the number of β -particles emitted by a source in 5 minutes.

GM tube connected to a scaler

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GM tube connected to a ratemeter

Photographic film

Ans wer 8

18.4 Detection of radiation (SB p. 30)

Radiation intake from food Expt 18F Radiation intake from food

Some food contains radioactive substances • content is low • but accumulate in bodies → long term effect

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To section 18.5

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