Radioactive Decay

• What is radioactive decay defined as?

  The spontaneous disintegration of a nucleus
• What particles can be emitted during radioactive decay?

  Alpha, beta, or gamma particles
• What does it mean that radioactive decay is a random process?

  Any nucleus has an equal decay probability
• Can we predict which nucleus will decay next?

  No, it cannot be known which will decay
• Can we know when a particular nucleus will decay?

  No, it cannot be known at what time
• What affects the rate of radioactive decay?

  The rate is unaffected by surrounding conditions
• How can we estimate the proportion of nuclei decaying?

  Only through estimation in a time period
• How can the random nature of radioactive decay be demonstrated?

  By observing the count rate of a GM tube
• What happens when a GM tube is placed near a radioactive source?

  Counts are irregular and cannot be predicted
• What does each count in a GM tube represent?

  A decay of an unstable nucleus
• What do fluctuations in count rate indicate?

  Evidence for the randomness of decay

  
• What is the average decay rate in radioactive decay?

  • Average number of nuclei expected to decay per unit time
  • Useful for understanding decay behavior
• What is the decay constant λ defined as?

  The probability of a nucleus decaying per unit time
• What does a high decay constant indicate?

  A high level of activity in the sample
• How is the activity A of a radioactive sample defined?

  The average number of nuclei that decay per unit time
• How can activity A be calculated?

  A = $\frac{\Delta N}{\Delta t}$ = $\lambda N$
• What is the unit of activity for a radioactive sample?

  Becquerels (Bq)
• What does an activity of 1 Bq represent?

  One decay per second
• What does the equation A = $\lambda N$ show?


  Greater decay constant means greater activity
• What does the minus sign in the decay equation indicate?

  The number of nuclei decreases with time
• What is the significance of the Curie (Ci) unit?

  • Defined by Marie and Pierre Curie
  • Represents the activity of 1 gram of radium
• How many atoms decayed in 1 minute for a 1 g sample of radium-226?

  $2.22 \times 10^{12}$ atoms
• What was the activity of a radium-226 sample containing $3.2 \times 10^{22}$ atoms?


  12 Ci
• How do you calculate the value of 1 Ci?

  1 Ci = $3.7 \times 10^{10} \text{ Bq}$
• What is the decay constant of radium-226?

  $1.388 \times 10^{-11} \text{ s}^{-1}$
• What are the steps to calculate the decay constant?

  1. Write down known quantities
  2. Use the activity equation A = λN
  3. Solve for λ