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Half-Life and Nuclear Reactions

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Half-Life and Nuclear Reactions Review We learned that all radioactive atoms eventually decay into stable isotopes. We did not talk about how long this takes. – PowerPoint PPT presentation

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Title: Half-Life and Nuclear Reactions


1
Half-Life and Nuclear Reactions
2
Review
  • We learned that all radioactive atoms eventually
    decay into stable isotopes.
  • We did not talk about how long this takes.

3
Half-Life
  • Cannot predict when a radioisotope (RI) will
    decay.
  • Can only give probability.
  • Half-life Amount of time during which one-half
    of a radioactive substance will decay.
  • During a RIs half-life, every atom has a 50
    chance of decaying.
  • Half-lives can be as short as a fraction of a
    second or as long as billions of years.

4
Half-Lifes
  • N-13 is radioactive.
  • It decays into C-13 via a process called electron
    capture.
  • The half-life of 13N is 10 minutes.
  • If you start with 1000 atoms of N-13, approx. how
    many will remain after 10 minutes?
  • 10 minutes 1 half-life, so there would be about
    500 atoms left.
  • Approx. how many will remain after 20 minutes?
  • 20 minutes 2 half-lives, so there would be
    about 250 atoms left.
  • Approx. how many will remain after 30 minutes?
  • 30 minutes 3 half-lives, so there would be
    about 125 atoms left.

5
Half-Lifes
6
Half-Lifes
  • The half-life of 26Al is 710,000 years.
  • If you start with 28.0 grams of 26Al, how much
    will remain after 1,420,000 years?
  • At start, 28.0 grams remain.
  • At 710,000 years, 14.0 grams remain.
  • At 1,420,000 years, 7.0 grams remain.

7
Half-Lifes
  • The half-life of 61Fe is 6.0 minutes. How much
    time must pass before a 600-mg sample decays to
    75 mg?
  • At start, 600 mg remain.
  • At 6.0 minutes, 300 mg remain.
  • At 12.0 minutes, 150 mg remain.
  • At 18.0 minutes, 75 mg remain.

8
Half-Lifes
  • In 48 minutes, 12 mg of 212Rn will decay to 3 mg.
    What is the half-life of 212Rn?
  • At start, 12 mg remain.
  • At (1st half-life), 6 mg remain.
  • At (2nd half-life), 3 mg remain.
  • It takes 2 half-lives for 12 mg to decay to 3 mg.
  • 2 half-lives 48 minutes
  • 1 half-life 24 minutes

9
Nuclear Fission
  • A heavy nucleus is struck by a neutron.
  • It becomes unstable and splits into smaller
    fragments, releasing energy.
  • In some cases extra neutrons are also released.
  • The neutrons can strike other nuclei and cause
    them to split.
  • Chain reaction.

10
Nuclear Fission
11
Uses for Nuclear Fission
  • Nuclear reactors use fission to produce energy.

12
Uses for Nuclear Fission
  • Weapons the bombs that destroyed Hiroshima and
    Nagasaki, Japan, were fission bombs.

13
Nuclear Fusion
  • Two light nuclei are joined to produce a larger
    nucleus.
  • Energy is released.

14
Nuclear Fusion
Energy
15
Uses for Nuclear Fusion
  • Nuclear fusion can be performed at low
    temperatures, but it does not produce much
    useable energy.
  • Fusion only produces significant energy at
    extremely high temperature and pressure.
  • The Sun produces energy via nuclear fusion.

16
Fusion in the Sun
  • The Sun is mostly made of hydrogen.
  • Intense heat and pressure at its center causes
    nuclear fusion to occur.
  • This releases energy that supports the mass of
    the Sun and prevents it from collapsing.

17
The Sun
18
Uses for Nuclear Fusion
  • Weapons Thermonuclear (hydrogen) bombs.
  • Use a conventional fission bomb to trigger
    nuclear fusion in a lithium hydride shell.
  • Much more destructive than fission bombs.
  • Never used in war.
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