# Half Life - NGfL Cymru

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```					Additional Science
Chapter 13

Physics 2
Half Life
What is “Half Life”?

The time taken for
atoms to decay

OR
The time

takes to reach
half its dose
Chapter 13
Example of half-life, using a pan of
popping popcorn
Half-life of the popcorn = 10s
16

12

Number of popcorn left
8

4

0
Chapter 13

0   10      20        30        40        50

Time (seonds)
Exercise                                                   Half life of the popcorn = 20s
32
The half life of the
popcorn is 20s

Number of popcorn left
24
The sample
contains 32
popcorn at the                                  16
start.
How many will be
8
left after 60s?
?

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

50s              10s

40s               20s

Answer = 4                      30s
Question on half life
The half life of americium is 433 years.
The example contains 480 nuclei.
480

1. How many will be left
after 1300 years?

Number of nuclei remaining
360

2. How many years will                                            240
have passed before it is
harmless?
120

1. 60 nuclei

0
2.     6 x 433 years                                                   0              433                866               1299    1732   2165
= 2598 years                                                                                             Time (years)
Chapter 13

Explanation          Nuclei 480                                       240       120       60        30          16        8
Years                 433                       433       433           433       433         433
Half Life                                      1         2         3         4           5         6

```
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