Nuclear Radiation Notes

Nuclear Radiation

Focus Question

  • How was radioactivity discovered?

New Vocabulary

  • Radioisotope: Isotopes of atoms with unstable nuclei.
  • X-ray: High-energy electromagnetic radiation not produced by radioactive sources.
  • Penetrating power: The ability of radiation to pass through matter.

Review Vocabulary

  • Element: A pure substance that cannot be broken down into simpler substances by physical or chemical means.

The Discovery of Radioactivity

  • Nuclear chemistry studies the structure of atomic nuclei and their changes.
  • Table 1: Comparison of Chemical and Nuclear Reactions
    • Chemical Reactions
      • Occur when bonds are broken and formed.
      • Involve only valence electrons.
      • Associated with small energy changes.
      • Atoms keep the same identity, may gain, lose, or share electrons, and form new substances.
      • Temperature, pressure, concentration, and catalysts affect reaction rates.
    • Nuclear Reactions
      • Occur when nuclei combine, split, and emit radiation.
      • Can involve protons, neutrons, and electrons.
      • Associated with large energy changes.
      • Atoms of one element are often converted into atoms of another element.
      • Temperature, pressure, and catalysts do not normally affect reaction rates.
  • Wilhelm Roentgen discovered X-rays in 1895.
  • Henri Becquerel, Marie Curie, and Pierre Curie pioneered the fields of radioactivity and nuclear chemistry.
  • In 1898, the Curies identified two new elements, polonium and radium, based on their radioactivity.

Types of Radiation

  • Isotopes of atoms with unstable nuclei are called radioisotopes.
  • Unstable nuclei emit radiation to attain more stable atomic configurations in a process called radioactive decay.
  • During radioactive decay, unstable nuclei release energy by emitting radiation.
  • The three most common types of radiation are alpha \alpha, beta \beta, and gamma \gamma.
  • Ernest Rutherford identified alpha, beta, and gamma radiation when studying the effects of an electric field on emissions from a radioactive source. *Alpha Particles
    • An alpha particle \alpha has the same composition as a helium nucleus—two protons and two neutrons.
    • The charge of an alpha particle is 2+ due to the presence of the two protons.
    • Alpha radiation consists of a stream of alpha particles.
    • Alpha particles are not very penetrating; a single sheet of paper stops alpha particles.
      *Example Decay:
    • Radium-226 (_{88}^{226}Ra) nucleus undergoes alpha decay to form radon-222 and an alpha particle.
    • _{88}^{226}Ra \rightarrow _{86}^{222}Rn + _{2}^{4}He
      *Beta Particles
    • A beta particle is a very fast-moving electron emitted when a neutron in an unstable nucleus converts into a proton.
    • Beta particles are represented by the symbol \beta or e^-. They have a 1- charge.
    • Beta radiation consists of a stream of fast-moving electrons.
    • A thin sheet of metal foil is required to stop beta particles.
      *Example Decay:
    • Iodine-131 nucleus undergoes beta decay to form xenon-131 and a beta particle.
    • _{53}^{131}I \rightarrow _{54}^{131}Xe + \beta
      *Gamma Rays
    • Gamma rays are high-energy electromagnetic radiation denoted by the symbol \gamma.
    • Emission of gamma rays does not change the atomic number or mass number of a nucleus.
    • Gamma rays almost always accompany alpha and beta radiation.
    • They account for most of the energy loss as a nucleus decays.
    • Some, but not all, gamma rays are stopped by a thick layer of concrete or lead.
      *X-rays
    • X-rays are high-energy electromagnetic radiation that are not produced by radioactive sources.
    • Their energy is lower than that of gamma rays.
    • X-rays are emitted when inner electrons are knocked out, and electrons from higher energy levels drop down to fill the vacancy.

Penetrating Power

  • The ability of radiation to pass through matter is called penetrating power.
  • Penetrating power is quantified as the depth of water that stops 50 percent of incoming radiation.
  • Gamma rays have the highest penetrating power because they have no charge or mass.