Physics - Topic 6 - Radioactivity

• What is the charge of a proton?

  +1
• What is the charge of a neutron?

  0
• What is the charge of an electron?

  • 1
• What is the relative mass of a proton?

  1
• What is the relative mass of a neutron?

  1
• What is the relative mass of an electron?

  0.0005
• What is the approximate size of an atom?

  ~0.1 nanometers
• What defines isotopes of an element?

  Isotopes have the same number of protons but different numbers of neutrons
• What is the mass number represented by in isotopes?

  A
• What does Z represent in isotopes?

  The proton number
• How does an atom become ionized?

  When an electron gains enough energy to leave the atom
• What happens when electrons move to a higher orbit?

  The atom absorbs electromagnetic radiation
• What happens when electrons fall to a lower orbit?

  The atom emits electromagnetic radiation
• What is alpha decay?

  It is the emission of a helium nucleus
• What is the ionizing power of alpha particles?

  Highly ionizing
• What is the penetrating power of alpha particles?

  Weakly penetrating
• What is beta minus decay?

  A neutron becomes a proton and releases an electron
• What is the ionizing power of beta particles?

  Medium ionizing
• What is the penetrating power of beta particles?

  Medium penetration
• What is gamma radiation?

  Electromagnetic radiation
• What is the ionizing power of gamma radiation?

  Low ionizing
• What is the penetrating power of gamma radiation?

  Highly penetrating
• What are examples of background radiation?

  Cosmic rays, radiation from underground rocks, nuclear fallout, medical rays
• How does photographic film measure radiation?

  It darkens when it absorbs radiation
• How does a Geiger-Muller tube detect radiation?

  It produces a clicking sound for each radiation pulse detected
• What are the key historical developments in atomic theory from 1800 to 1913?

  • 1800: Dalton proposed that everything is made of atoms.
  • 1897: JJ Thomson discovered the electron, leading to the Plum Pudding Model.
  • 1911: Rutherford discovered that most of the atom is empty space through the Gold Foil Experiment.
  • 1913: Bohr produced the final model of the atom.
• What does the Gold Foil Experiment demonstrate about atomic structure?

  It shows that most of the atom is empty space and that the nucleus is positively charged

  
• What is beta-plus decay?

  A proton becomes a neutron and releases a positron
• What is the equation for alpha decay?

  $^{A}_{Z}X \rightarrow ^{A-4}_{Z-2}Y +$ \alpha\
• What is the equation for beta decay?

  $^{A}_{Z}X \rightarrow ^{A}_{Z+1}Y +$$e^{-} +$ \bar{\nu}\
• What is the equation for gamma decay?

  $^{A}_{Z}X \rightarrow ^{A'}_{Z'}Y +$ \gamma\
• What is activity in the context of radioactivity?

  Activity is the number of decays in a sample per second
• What is half-life?

  The time taken for half the nuclei in a sample to decay
• How do you calculate net decline after X half-lives?

  $\text{net decline} =$$\frac{\text{initial number} - \text{number after X half-lives}}{\text{initial number}}$
• What is the net decline after 3 half-lives if the initial number of nuclei is 80?

  $\text{Net decline} =$$\frac{80 - 10}{80} =$$\frac{70}{80} =$$\frac{7}{8}$
• What are the uses of radioactivity?

  • Smoke alarms using Americium
  • Irradiating food to kill bacteria
  • Sterilization of equipment using gamma radiation
  • Tracing and gauging thickness in production processes
  • Diagnosis and treatment of cancer using gamma emitters
• What are the dangers of ionizing radiation?

  • Short half-life: Less long-term risk as it decays quickly
  • Long half-life: Remains weakly radioactive for a long time, posing a long-term risk
• Why is Americium suitable for use in smoke alarms?

  It has a long half-life and is an alpha emitter
• How do gamma rays sterilize food?

  They transfer energy to bacteria, killing them
• How is beta radiation used in gauging thickness?

  It passes through paper and detects changes in thickness