Problems and Video

DAY 1

•         How many atoms of C-14 will be left in 120,000 years if the half-life is 40,000 years and there are 64 atoms?(Problem 1)

•         If you have 1000 radioactive atoms now, how many radioactive atoms will be around in 3 half-lifes?(Problem 2)

•         How many years have gone by in problem 2 if the half-life is 20 years?(Problem 3)

ANSWERS

•         How many atoms of C-14 will be left in 120,000 years if the half-life is 40,000 years and there are 64 atoms?(Problem 1)

•         Years           atoms

•         0                              64

•         40,000         32

•         80,000         16

•         120,000                   8                  Answer= 8 atoms

•         If you have 1000 radioactive atoms now, how many radioactive atoms will be around in 3 half-lifes?(Problem 2)

•         Half-lifes                 Atoms

•         0                              1000

•         1                              500

•         2                              250

•         3                              125              Answer= 125 atoms

•         How many years have gone by in problem 2 if the half-life is 20 years?(Problem 3)

•         Half-lifes                 Atoms Years

•         0                              1000              0

•         1                              500                20

•         2                              250                40

•         3                              125                60

•         Answer= 60 Years

DAY 2

•         How many atoms of U-238 will be left in 100,000 years if the half-life is 20,000 years and there are 128 atoms?(Problem 1)

•         If you have 16,000 radioactive atoms now, how many radioactive atoms will be around in 3 half-lifes?(Problem 2)

•         How many years have gone by if the half-life is 20 years, and 400 atoms decayed into 100 atoms?(Problem 3)

•         How many atoms of U-238 will be left in 100,000 years if the half-life is 20,000 years and there are 128 atoms?(Problem 1)

•         Years   Atoms Half-life

•         0                  128                          0

•         20,000 64                            1

•         40,000 32                            2

•         60,000 16                            3

•         80,000 8                              4

•         100,000       4                          5      ANS=4 atoms

If you have 16,000 radioactive atoms now, how many radioactive atoms will be around in 3 half-lifes?(Problem 2)

•         Atoms Half-life

•         16,000         0

•         8,000           1

•         4,000           2

•         2,000           3

•         Answer is 2000 atoms.

•         How many years have gone by if the half-life is 20 years, and 400 atoms decayed into 100 atoms?(Problem 3)

•         Atoms Half-life  Years

•         400              0      0

•         200              1      20

•         100              2      40

•         The answer is 40 years

DAY 3

•         How many atoms of U-238 were around 60,000 years ago if the half-life is 20,000 years and there are currently 200 atoms? (Prob. 1)

•         If you have 64,000 radioactive atoms now, how many radioactive atoms will be around in 8 half-lifes? (Problem 2)

•         How many years have gone by if the half-life is 10 years, and 1600 atoms decayed into 200 atoms? (Problem 3)

•         How many atoms of U-238 were around 60,000 years ago if the half-life is 20,000 years and there are currently 200 atoms?(Prob. 1)

•         Years   Atoms Half-life

•         0                  200                          0

•         20,000 400                          1

•         40,000 800                          2

•         60,000 1600                        3

         ANS=1600 atoms

•         If you have 64,000 radioactive atoms now, how many radioactive atoms will be around in 8 half-lifes?(Problem 2)

•         Atoms Half-life

•         64,000 0

•         32,000         1

•         16,000 2

•         8,000   3

•         4,000   4

•         2,000      5     

•         1,000   6

•         500              7

•         250              8

•         ANS=250 atoms

•         How many years have gone by if the half-life is 10 years, and 1600 atoms decayed into 200 atoms?(Problem 3)

•         Years   Atoms Half-life

•         0                  1600                        0

•         10                800                          1

•         20                400                          2

•         30                200                          3

•                  ANS= 30 years

DAY 4

•         How many atoms of U-235 were around 4 million years ago if the half-life is 500,000 years and there is currently 1 atom? (Prob. 1)

•         If you have 200,000 radioactive atoms now, how many radioactive atoms will be around in 4 half-lifes? How many were around 3 half-lifes ago? (Problem 2)

•         How many years ago were there ½ the original  atoms (parent isotopes) if the half-life is 10 years, and there are now 1/32 of the original atoms? (Problem 3)

•         How many atoms of U-235 were around 4 million years ago if the half-life is 500,000 years and there is currently 1 atom?(Prob. 1)

•         Years           Atoms Half-life

•         0                              1      0

•         500,000                   2      1

•         1,000,000                4      2

•         1,500,000                8      3

•         2,000,000                16    4

•         2,500,000                32    5

•         3,000,000                64    6

•         3,500,000                128  7

•         4,000,000                256  8

         ANS= 256 atoms

•         If you have 200,000 radioactive atoms now, how many radioactive atoms will be around in 4 half-lifes? (Problem 2)

•         Atoms Half-life

•         200,000                   0

•         100,000                   1

•         50,000                     2

•         25,000                     3

•         12,500         4

         ANS= 12,500 atoms

•         If you have 200,000 radioactive atoms now.  How many were around 3 half-lifes ago? (Problem 2)

•         Atoms Half-life

•         200,000                   0

•         400,000                   1

•         800,000                   2

•         1,600,000    3

         ANS= 1,600,000 atoms

•         How many years ago were there ½ the original  atoms(parent isotopes) if the half-life is 10 years, and there are now 1/32 of the original atoms? (Problem 3)

•         Years   Atoms         Half-life

•         0                  1/32                        0

•         10                1/16                        1

•         20                1/8                          2

•         30                1/4                          3

•         40                1/2                          4

         ANS= 40 years

DAY 5

•         How many atoms of H-2 were around 40 years ago if the half-life is 10 years and there are currently 20 atoms?(Prob. 1)

•         If you have 50,000 radioactive atoms now, how many radioactive atoms will be around in 2 half-lifes? How many were around 4 half-lifes ago? (Problem 2)

•         How many years ago were there 128 atoms if the half-life is 1,000 years, and there are now 2 atoms? (Problem 3)

•         How many atoms of H-2 were around 40 years ago if the half-life is 10 years and there are currently 20 atoms?(Prob. 1)

•         Years   Atoms Half-life

•         0                  20                            0

•         10                40                            1

•         20                80                            2

•         30                160                          3

•         40                320                          4

         ANS= 320 atoms

•         If you have 50,000 radioactive atoms now, how many radioactive atoms will be around in 2 half-lifes? How many were around 4 half-lifes ago? (Problem 2)

•         Atoms Half-life

•         50,000                     0

•         25,000                     1

•         12,500                     2

         ANS= 12,500 atoms

•         If you have 50,000 radioactive atoms now, how many radioactive atoms will be around in 2 half-lifes? How many were around 4 half-lifes ago? (Problem 2)

•         Atoms Half-life

•         50,000                     0

•         100,000                   1

•         200,000                   2

•         400,000                   3

•         800,000                   4

         ANS= 800,000 atoms

•         How many years ago were there 128 atoms if the half-life is 1,000 years, and there are now 2 atoms? (Problem 3)

•         Years   Atoms         Half-life

•         0                  2                             0

•         1,000   4                              1

•         2,000   8                              2

•         3,000   16                            3

•         4,000   32                            4

•         5,000   64                            5

•         6,000   128                          6

         ANS=6000 YEARS

DAY 6

•         How many atoms of C-14 were around 160,000 years ago if the half-life is 40,000 years and there are currently 4 atoms?(Problem 1)

•         If you have 1000 radioactive atoms now, how many radioactive atoms were around 4 half-lifes ago?(Problem 2)

•         How many years have gone by in problem 2 if the half-life is 2000 years?(Problem 3)

•         How many atoms of C-14 were around 160,000 years ago if the half-life is 40,000 years and there are currently 4 atoms?(Problem 1)

Time                        atoms

•         0                              4

•         40,000         8

•         80,000         16

•         120,000                   32               

•         160,000                   64  Answer= 64 atoms

•         If you have 1000 radioactive atoms now, how many radioactive atoms were around 4 half-lifes ago?(Problem 2)

•         Half-lifes                 Atoms

•         0                              1000

•         1                              2000

•         2                              4000

•         3                              8000           

•         4                              16,000 Answer= 16,000 atoms

How many years have gone by in problem 2 if the half-life is 2000 years?(Problem 3)

Half-lifes                 Atoms Time

•         0                              1000            0

•         1                              2000            2,000

•         2                              4000            4,000

•         3                              8000            6,000

•         4                              16,000         8,000

•         Answer= 8,000 years

DAY 7

•         How many atoms of Po-208 were around 2 hours ago if the half-life is 20 minutes and there are currently 2000 atoms? (Prob. 1)

•         If you have 64 radioactive atoms now, and in 10 days you have 16 atoms, what is the length of the half-life? (Problem 2)

•         How many minutes have gone by if the half-life is 4 minutes, and 3200 atoms decayed into 50 atoms? (Problem 3)

•         How many atoms of Po-208 were around 2 hours ago if the half-life is 20 minutes and there are currently 2000 atoms? (Prob. 1)

•         Time            Atoms         Half-life

•         0                  2,000           0

•         20 min.        4,000           1

•         40 min.        8,000           2

•         60 min.        16,000         3

•         80 min.        32,000         4

•         100 min.         64,000          5

•         120 min        128,000          6

         ANS= 128,000 atoms

If you have 64 radioactive atoms now, and in 10 days you have 16 atoms, what is the length of the half-life? (Problem 2)

Atoms Half-life

•         64                0

•         32                1

•         16                2

•         ANS=10 days/2 half-lifes= 5 days

•         How many minutes have gone by if the half-life is 4 minutes, and 3200 atoms decayed into 50 atoms? (Problem 3)

•         Minutes       Atoms                     Half-life

•         0                  3200                                    0

•         4                  1600                                    1

•         8                  800                                      2

•         12                400                                      3

•         16                200                                      4

•         20                100                                      5

•         24                50                                        6

•                  ANS= 24 minutes

DAY 8

•         How many atoms of U-235 were around 1 million years ago if the half-life is 100,000 years and there is currently 4 atoms? (Prob. 1)

•         If you have 1,000 radioactive atoms now, how many radioactive atoms will be around in 3 half-lifes? How many atoms were around 4 half-lifes ago? (Problem 2)

•         How long is a half-life if 8000 atoms decay into 125 atoms in 18 years? (Problem 3)

•         How many atoms of U-235 were around 1 million years ago if the half-life is 100,000 years and there is currently 4 atom? (Prob. 1)

•         Time                       Atoms Half-life

•         0                              4      0

•         100,000                   8      1

•         200,000                   16    2

•         300,000                   32    3

•         400,000                   64    4

•         500,000                   128  5

•         600,000                   256  6

•         700,000                   512  7

•         800,000                   1024 8

•         900,000                   2048 9

•         1,000,000                4096 10

         ANS= 4096 atoms

If you have 1,000 radioactive atoms now, how many radioactive atoms will be around in 3 half-lifes? How many atoms were around 4 half-lifes ago? (Problem 2) Atoms  Half-life

•         1,000           0

•         500              1

•         250              2

•         125                          3

         ANS= 125 atoms

If you have 1,000 radioactive atoms now, how many radioactive atoms will be around in 3 half-lifes? How many atoms were around 4 half-lifes ago? (Problem 2)

Atoms Half-life

•         1,000           0

•         2,000           1

•         4,000           2

•         8,000           3

•         16,000         4

         ANS= 16,000 atoms

•         How long is a half-life if 8000 atoms decay into 125 atoms in 18 years? (Problem 3)

•         Years  Atoms         Half-life

•         0                  8,000                      0

•         3                  4,000                      1

•         6                  2,000                      2

•         9                  1,000                      3

•         12                500                         4

•         15                250                          5

•         18                125                          6

         ANS= 18/6 =3 years