Half Life - NGfL Cymru

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					Additional Science
Chapter 13




                 Physics 2
                             Half Life
                          What is “Half Life”?

                     The time taken for
                     half the radioactive
                       atoms to decay

                                            OR
                                                    The time
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                                                  radioactivity
                                                 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
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                                                           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?
                                            ?
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                                                                     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

                                         Answer1

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


                      1. 60 nuclei
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                                                                                         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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