Applications of Radioactivity

• What are some applications of radioactivity?

  Industry, agriculture, and medicine
• What is one use of radioactivity in medicine?

  Radiotherapy
• What is radiocarbon dating used for?

  Dating archaeological artefacts
• What isotope is commonly used in radioactive dating?

  Carbon-14
• How is carbon-14 formed?

  From cosmic rays colliding with nitrogen
• What happens to carbon-14 after an organism dies?

  It stops being absorbed
• What is the half-life of carbon-14?

  About 5730 years

  
• How can living material be dated using carbon-14?

  By comparing current and initial carbon-14 amounts

  
• What is the reliability range of carbon dating?

  500 to 60,000 years
• Why is carbon dating unreliable for samples less than 500 years old?

  Activity is too high to measure accurately
• Why is carbon dating unreliable for samples older than 60,000 years?

  Activity is too low to distinguish changes
• What method is critical for determining the age of the Earth?

  Uranium-lead dating
• What happens to uranium atoms in uranium-lead dating?

  They decay into lead atoms

  
• What is the half-life of uranium-238?

  4.5 billion years

  
• How is the age of a rock sample determined using uranium-lead dating?

  By measuring the ratio of lead to uranium
• What do radioisotope power systems do?

  Transform heat from decay into electrical power
• What isotope is typically used in radioisotope power systems?

  Plutonium-238
• How much power does 1 g of plutonium-238 generate?

  About 500 mW
• What is the process to estimate the time a plutonium-238 source can power a space probe?

  1. List known quantities (mass, half-life, energy per decay)
  2. Calculate initial number of nuclei
  3. Calculate initial activity
  4. Calculate initial power output
  5. Use exponential decay equation to find time
• What is the initial number of nuclei in 4.0 kg of plutonium-238?

  Approximately $1.012 \times 10^{25}$ nuclei
• How is the initial activity of a plutonium-238 source calculated?

  Using the decay constant and number of nuclei
• What is the initial power output of the plutonium-238 source?

  Approximately 2231 W
• What is the electrical power transferred to the probe from plutonium-238?

  Approximately 714 W
• How long is the plutonium-238 source expected to supply power to the space probe?

  About 73.3 years
• What are the steps involved in calculating the time of operation for a space probe powered by plutonium-238?

  1. List known quantities
  2. Calculate initial number of nuclei
  3. Calculate initial activity
  4. Calculate initial power output
  5. Use exponential decay equation