Radioactive decay

• What is the activity of a radioactive source?

  The number of atoms that decay per second
• What is half-life?

  The time it takes for the active nuclei in a sample to halve
• What is meant by the random nature of radioactive decay?

  It is unpredictable which nuclei will decay and when
• What sort of curve does a radioactive decay plot?

  Exponential decay
• What is the decay constant?

  The fixed probability that a nucleus will decay in a second
• What is the equation of the activity 'N' nuclei?

  $A=$$Nλ$
• What is the unit for decay constant?

  $s^-1$