Topic 6 – Radioactivity

• What is the structure of an atom?

  An atom consists of a positively charged nucleus surrounded by negatively charged electrons.

  
• What particles make up the nucleus of an atom?

  The nucleus is made of positive protons and neutral neutrons.

  
• How do electrons orbit the nucleus?

  Electrons orbit the nucleus at different fixed distances.
• What is the relationship between the nuclear radius and the radius of the atom?

  The nuclear radius is much smaller than the radius of the atom.
• Where does most of the mass of an atom lie?

  Almost all the mass of the atom lies in the nucleus.
• What are the relative masses and charges of protons, neutrons, electrons, and positrons?

  • Proton: Relative Mass = 1, Relative Charge = +1
  • Neutron: Relative Mass = 1, Relative Charge = 0
  • Electron: Relative Mass = 0.0005, Relative Charge = -1
  • Positron: Relative Mass = 0.0005, Relative Charge = +1
• What defines isotopes of an element?

  Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.

  
• Give examples of isotopes of carbon.

  Carbon-12, Carbon-13, and Carbon-14 are examples of isotopes of carbon.
• How does the charge of a neutral atom relate to its protons and electrons?

  A neutral atom has the same number of electrons and protons, resulting in no overall charge.
• What happens when an electron gains enough energy?

  If an electron gains enough energy, it can leave the atom and form an ion.
• What are the different forms of radioactive decay?

  • Alpha decay: releases a helium nucleus
  • Beta Minus decay: neutron becomes a proton and releases an electron
  • Beta Plus decay: proton becomes a neutron and releases a positron
  • Gamma decay: releases electromagnetic radiation

  
• What is the nature of decay in radioactivity?

  Decay occurs in a random process.

  
• What are the characteristics of alpha radiation?

  Alpha radiation is highly ionising and weakly penetrating.

  
• What are the characteristics of beta radiation?

  Beta radiation is medium ionising and has medium penetration.

  
• What are the characteristics of gamma radiation?

  Gamma radiation is low ionising and highly penetrating.

  
• What are some examples of background radiation?

  Examples of background radiation include cosmic rays, radiation from underground rocks, nuclear fallout, and medical rays.
• What are the methods of measuring radioactivity?

  • Photographic film: darkens with radiation exposure
  • Geiger-Muller Tube: detects radiation and produces clicks based on radiation levels

  
• What was Dalton's contribution to atomic theory?

  • Dalton proposed that everything is made of atoms in 1800.
• What did JJ Thomson discover?

  • JJ Thomson discovered the electron in 1897.
• What was the Plum Pudding Model?

  • Proposed by JJ Thomson
  • Suggested that electrons were dispersed in a positively charged "pudding"
• What is the significance of the Gold Foil Experiment?

  The Gold Foil Experiment demonstrated that atoms have a small, dense, positively charged nucleus.

  
• What did Bohr contribute to atomic theory?

  • Bohr produced the final model of the atom in 1913.
  • Proposed that electrons exist in fixed orbitals around the nucleus.
• What occurs during beta-minus decay?

  • A neutron becomes a proton and releases an electron.
• What occurs during beta-plus decay?

  • A proton becomes a neutron and releases a positron.
• What is alpha decay?

  • An alpha particle is equivalent to a helium nucleus.
• What is beta decay?

  • A beta particle is an electron emitted from the nucleus.

  
• What is gamma decay?

  • A gamma ray is electromagnetic radiation emitted during decay.
• What is activity in the context of radioactivity?

  Activity is the number of decays in a sample per second.

  
• How does activity change over time?

  Activity decreases exponentially over time.
• What are the units of activity?

  The units of activity are Becquerel (Bq).
• What is half-life in the context of radioactivity?

  The half-life of an isotope is the time taken for half the nuclei in a sample to decay.
• Can the decay of a single nucleus be predicted?

  No, the decay of a single nucleus cannot be predicted, but the half-life allows for predictions of large numbers of nuclei.
• How do you calculate net decline of radioactive nuclei after X half-lives?

  • Net decline = (Initial number - Number after X half-lives) / Initial number
  • Continue halving the initial number for X half-lives.
• What are some uses of radioactivity?

  • Smoke alarms use Americium as an alpha emitter.
  • Gamma rays are used for irradiating food and sterilising equipment.
  • Beta radiation is used for tracing and gauging thickness.
  • Gamma emitters are used in cancer diagnosis and treatment.

  
• What are the dangers of ionising radiation?

  • Short half-life: Less long-term risk as it quickly becomes less radioactive.
  • Long half-life: Remains weakly radioactive for a long time, posing a long-term risk.
• What is one application of gamma emitters in medical diagnostics?

  They can be consumed or injected to reveal tumors in the body.
• How do gamma rays help in the treatment of cancer?

  Gamma rays are used to kill cancer cells in tumors.
• What is a potential risk of exposing healthy cells to gamma rays?

  Healthy cells may mutate or become damaged.
• What is a characteristic of a radioactive source with a short half-life?

  It presents less of a long-term risk as it quickly becomes less radioactive.
• Why is Americium suitable for use in smoke alarms?

  It has a long half-life and weak activity, making it safe and not needing replenishment.