topic 6 radioactivity

• What is the charge of the nucleus in an atom?

  Positively charged
• What particles are found in the nucleus of an atom?

  Protons and neutrons
• How does the size of the nucleus compare to the atom?

  Nucleus radius is much smaller than atom
• What is the typical size of atoms?

  $1 \times 10^{-10} \text{ m}$
• What distinguishes isotopes of an element?

  Different numbers of neutrons
• What are the relative masses and charges of protons, neutrons, and electrons?

  • Proton: Mass = 1, Charge = +1
  • Neutron: Mass = 1, Charge = 0
  • Electron: Mass = 0.0005, Charge = -1
• Why is an atom neutral?

  Number of protons equals number of electrons
• How do electrons orbit the nucleus in an atom?

  At different distances from the nucleus
• What happens when an inner electron absorbs EM radiation?

  It moves to a higher energy level
• What occurs when an electron is excited?

  It moves to an empty shell
• What happens when an excited electron falls back to its original energy level?

  It emits the same amount of energy absorbed
• What is produced when an outer electron leaves the atom?

  A free electron and a positive ion
• What type of radiation do radioactive substances emit during decay?

  Alpha, beta, gamma, or neutrons
• What is background radiation?

  Low-level radiation present in the environment
• What are the origins of background radiation?

  Natural and man-made sources
• What are the sources of background radiation?

  • Naturally occurring unstable isotopes
  • Cosmic rays from space
  • Human activity (nuclear fallout)
• How does a Geiger Muller tube measure radiation?

  Transmits electrical pulses to a counting machine
• What does the count rate in a Geiger Muller tube indicate?

  The amount of radiation absorbed
• How does photographic film detect radiation?

  Becomes darker with absorbed radiation
• What is the purpose of a radiation badge?

  To monitor a person's radiation exposure
• What types of radiation are monitored by a radiation badge?

  • Alpha radiation (absorbed by paper)
  • Beta radiation (absorbed by aluminum)
  • Gamma radiation (reduced by lead)
• What is an alpha particle?

  A helium nucleus
• What is a beta particle?

  An electron emitted from the nucleus
• What is a gamma ray?

  Electromagnetic radiation
• Which type of radiation is the least penetrating?

  Alpha radiation
• What is the range of beta-minus radiation in air?

  A few meters
• How does beta-plus radiation differ from beta-minus radiation?

  Beta-plus emits a positron
• What is the penetration ability of gamma rays?

  Strongly penetrating, travels long distances
• What are the models of the atom and their key contributors?

  1. Plum pudding model: J.J. Thomson
  2. Rutherford's alpha particle scattering
  3. Niels Bohr's nuclear model
• What occurs during beta-minus decay?

  A neutron changes into a proton and electron
• What happens in beta-plus decay?

  A proton becomes a neutron and positron
• How do alpha, beta-minus, beta-plus, and neutron emissions affect atomic and mass numbers?

  • Alpha: Mass -4, Atomic -2
  • Beta-minus: Mass unchanged, Atomic +1
  • Beta-plus: Mass unchanged, Atomic -1
  • Neutron emission: Mass -1, Atomic unchanged
  • Gamma rays: No change
• What happens to nuclei after radioactive decay?

  They often undergo nuclear rearrangement
• How does the activity of a radioactive source change over time?

  It decreases as nuclei decay
• What is the unit of activity for a radioactive isotope?

  Becquerel (Bq)
• What is half-life in radioactivity?

  Time for radioactive nuclei to halve
• What are the characteristics of short and long half-lives?

  • Short half-life: Rapid decay, high initial radiation
  • Long half-life: Slow decay, low radiation over time
• Can the decay of a particular nucleus be predicted?

  No, but half-life can predict activity
• What are the uses of radioactivity?

  1. Household fire alarms
  2. Irradiating food
  3. Sterilizing equipment
  4. Medical tracers
  5. Gauging thickness
• What can ionising radiation cause in living cells?

  Tissue damage