Nuclear Decay and Half-life

• Which number defines what element an atom is: the atomic number or the mass number?

  Atomic number
• What is the atomic number of an atom? What is the mass number of an atom?

  Atomic number: Number of protons in an atom. Mass number: Sum of protons and neutrons in an atom.
• What is an isotope? Are they stable?

  An isotope is a variant of an element with the same number of protons but a different number of neutrons. Some isotopes are stable, while others are unstable and undergo radioactive decay.
• For the three types ionising radiation, give: a.) their ionising power, b.) their range in air (penetration)

  1. Alpha - very ionising, a few cm in air
  2. Beta - fairly ionising, few meters in air
  3. Gamma - weakly ionising, many kilometres in air
• What is the activity of a source? How does activity relate to count-rate?

  The activity of a source refers to the rate at which it undergoes radioactive decay. The count-rate is directly proportional to the activity of the source.
• Define half-life and describe how to find a source‘s half-life, given a graph of its activity over time?

  Half-life is the time it takes for half of the radioactive atoms in a sample to decay. To find a source's half-life from a graph, identify the time it takes for the activity to decrease to half of its initial value as the half-life time on the x-axis would align to the y-axis value of half the original