WJEC Science Double Award Unit 6 66 The time radioactivity takes to reach half its dose What is Half Life The time taken for half the radioactive atoms to decay OR Number of popcorn left ID: 914258
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Slide1
Half Life
WJEC Physics Unit 2 - 2.8
WJEC Science (Double Award) Unit 6 - 6.6
Slide2The time radioactivity takes to reach half its dose
What is “Half Life”?
The time taken for half the radioactive atoms to decay
OR
Slide3Number of popcorn left
16
12
8
4
0
0 10 20 30 40 50
Time (seonds)
Half-life of the popcorn = 10s
Example of half-life using a pan of popping corn
Slide420s
40s
30s
10s
50s
0s
Exercise
Number of popcorn left
32
24
16
8
0
0 20 40 60 80 100
Time (seconds)
Half life of the popcorn = 20s
The half life of the popcorn is 20s
The sample contains 32 popcorn at the start.
How many will be left after 60s?
?
Answer = 4
Slide5Number of nuclei remaining
480
360
240
120
0
0 433 866 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 8
Years 433 433 433 433 433 433
Question on half life
Answer1
Answer 2
Explanation
Half Life 1 2 3 4 5 6
1. 60 nuclei
6 x 433 years
= 2598 years
The half life of americium is 433 years.
The example contains 480 nuclei.