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.