Earth Systems

1
Radioactive Isotopes

• Earth Systems

2
Journal 8 9/11/2012

• Describe what you think is meant by the term
  half-life. What does it represent? Why do you, as
  an Earth Science student, think you need to
  understand half-life?

3
Journal 9 9/12/2012

• Use the above diagram to answer the questions.
• What is the half-life of the represented isotope?
• The original sample has 100 atoms. How many atoms
  are left after 2 half-lifes?
• How long does it take the original sample to
  decrease to 25 atoms?

4
Radioactivity

• Radioactivity is the spontaneous process that
  occurs when an unstable nucleus releases
  particles and/or energy to form a more stable
  nucleus.

5
Radioisotopes

• A radioisotope is an unstable radioactive
  nucleus.
• Examples include
• carbon-14
• deuterium (hydrogen with 1 neutron)
• all elements with atomic numbers above 83

6
Radioactive Decay

• Radioactive decay is the release of subatomic
  particles and/or energy by radioactive isotopes.
• Alpha and beta decay result in transformed atom.
• Gamma decay results in same atom with release of
  energy.

ALPHA DECAY
BETA DECAY
GAMMA DECAY
7
Half-life

• Half-life is the time it takes for half of the
  radioactive particles in a radioactive nucleus to
  decay.
• Example
• If an original sample of carbon-14 has a mass of
  10 grams and its half-life is 5700 years, how
  many grams of carbon-14 would remain after one
  half-life?
• ANSWER 5 grams

8
Radiometric Dating

• Because the rate of radioactive decay is
  constant, scientists use it to determine the
  absolute age of any object in which radioactive
  decay occurs.
• This method of using radioactive isotopes to date
  an object is called radiometric dating.

9
Radiocarbon Dating

• The tissues of all living organisms contain small
  amounts of Carbon-14 (C-14).
• C-14 decays but is replenished by the process of
  respiration.
• When the organism dies, the respiration process
  ends so the amount of C-14 decreases.
• Scientists can measure the amount of C-14 in
  organic material to determine how much time has
  passed since the organisms death.
• This process is called radiocarbon dating.