Basic Ideas

• Atom


  Made up of three particles: protons, neutrons, electrons
• Proton


  • Relative mass 1, relative charge +1
• Neutron


  • Relative mass 1, relative charge 0
• Electron


  • Relative mass 1/1840, relative charge -1
• Atomic number


  Number of protons
• Atoms of the same element have the same number of protons
• Mass number


  Sum of protons and neutrons
• Atoms of the same element can have different numbers of neutrons. These are called isotopes
• Radioactive isotopes


  • Unstable, usually heavy nuclei like uranium and plutonium, spontaneously disintegrate and can emit alpha, beta, and gamma radiation
• Alpha (α) particles


  • Positively charged helium nuclei, mass of four units, stopped by a piece of paper, strongly ionising
• Beta (β) particles


  • Negatively charged electrons, negligible mass, stopped by 0.5 cm of aluminium
• Gamma (γ) radiation


  • Very high energy electromagnetic radiation, > 2cm of lead required to stop it, weakly ionising
• Radioactive decay


  1. Alpha decay

  2. Beta decay

  3. Positron emission

  4. Electron capture

  5. Gamma emission
• Half-life


  The time taken for the radioactivity of a radioactive isotope to fall to half of its initial value, or the time taken for half the atoms in a radioactive isotope to decay
• The half-life of a radioisotope is characteristic of each radioisotope and unaffected by catalysts or changes in temperature
• Half-life calculations


  1. Finding the time taken for the radioactivity to fall to a certain fraction of its initial value

  2. Finding the mass of a radioactive isotope remaining after a certain length of time given the initial mass
• Penetrating power/danger of radioactive emissions


  • Gamma radiation is likely to be the most hazardous if the source is outside the body, but alpha-emitting isotopes are far more dangerous if ingested
• Effects of ionising radiation


  • Can damage DNA, leading to changes in cell function, mutations, cancer, and cell death at higher doses
• Beneficial uses of radioactivity


  • Treatment of cancer
  • Tracer
  • Calculating age of plant and animal remains
  • Estimating geological age of rocks
  • Production of electricity
  • Measuring the thickness of metal foil