Half Life

1
Half Life
Physics 2
Additional Science
Chapter 13
2
What is Half Life?
The time taken for half the radioactive atoms to
decay
OR
The time radioactivity takes to reach half its
dose
Additional Science
Chapter 13
3
Example of half-life, using a pan of popping
popcorn
Half-life of the popcorn 10s
16 12 8 4 0




Number of popcorn left
Additional Science
Chapter 13

0 10 20
30 40 50

Time (seonds)
4
Exercise
Half life of the popcorn 20s
32 24 16 8 0




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

Additional Science
0 20 40
60 80 100
Chapter 13
Time (seconds)

Answer 4
5
Question on half life
The half life of americium is 433 years. The
example contains 480 nuclei.
480 360 240 120 0




1. How many will be left after 1300 years? 2.
How many years will have passed before it is
harmless?
Answer1
Number of nuclei remaining

Answer 2
Additional Science

1. 60 nuclei

• 6 x 433 years
• 2598 years

Chapter 13
0 433 866 1299 1732
2165
Time (years)
Explanation
Nuclei 480 240 120 60
30 16 8
Years 433 433 433 433
433 433
Half Life 1 2 3
4 5 6