Half LifeHalf LifePhysics 2Physics 2

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The time The time radioactivity radioactivity

takes to reach takes to reach half its dosehalf its dose

What is “Half Life”?What is “Half Life”?

The time taken for The time taken for half the radioactive half the radioactive

atoms to decayatoms to decay

OROR

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Num

ber o

f pop

corn

left

16

12

8

4

00 10 20 30 40 50

Time (seonds)

Half-life of the popcorn = 10s

Example of half-life, using a pan of Example of half-life, using a pan of popping popcornpopping popcorn

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20s40s

30s

10s50s

0s

ExerciseExercise

Num

ber o

f pop

corn

left

32

24

16

8

00 20 40 60 80 100

Time (seconds)

Half life of the popcorn = 20s

The half life of the popcorn is 20sThe sample contains 32 popcorn at the start. How many will be left after 60s?

?

Answer = 4Addi

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Num

ber o

f nuc

lei r

emai

ning

480

360

240

120

00 433 866 1299 1732 2165

Time (years)

1. How many will be left after 1300 years?

2. How many years will have passed before it is harmless?

Nuclei 480 240 120 60 30 16 8Nuclei 480 240 120 60 30 16 8

Years 433 433 433 433 433 433

Question on half lifeQuestion on half life

Answer1

Answer 2

Explanation

Half Life 1 2 3 4 5 6

1. 60 nuclei

2. 6 x 433 years

= 2598 years

The half life of americium is 433 years. The example contains 480 nuclei.

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