Radioactive

• Radioactive decay


  1. Unstable nucleus spontaneously changes to a more stable nucleus

  2. Releases high energy, ionizing radiation
• Ionizing radiation


  High energy particles that can enter cells, knock off electrons, and damage DNA
• Radioactivity


  Can be dangerous, but also useful (e.g. radiation therapy to target cancer cells)
• Chemical reactions


  • Number of elements on reactant and product side is the same
  • Cannot create new elements
• Protons


  Define the identity of an element
• Isotopes


  Atoms of the same element with different numbers of neutrons
• Mass number


  Total number of protons and neutrons in a nucleus
• Unstable nucleus


  Certain nuclei can be unstable and spontaneously change to a more stable form, releasing high energy radiation
• Unstable nuclei


  • Carbon-14
  • Heavy nuclei with many protons
• Beta decay


  Unstable parent nucleus spontaneously changes to a more stable daughter nucleus, releasing a beta particle
• Radioactive decay can be dangerous due to the ionizing nature of the released radiation, but can also be useful (e.g. radiation therapy)
• The periodic table does not go on forever because heavier elements become more unstable
• Elements above atomic number 83 do not have a stable isotope, all their isotopes are radioisotopes
• Coulomb's repulsion


  The electric force that tries to blow the nucleus apart
• Strong nuclear force


  The attractive force that keeps the nucleus together, it is the strongest force in nature
• The strong nuclear force acts on both protons and neutrons, while the Coulomb's repulsion only acts on protons
• The strong nuclear force is a short-ranged force, while the Coulomb's repulsion is long-ranged
• As the nucleus gets heavier, the Coulomb's repulsion becomes stronger and can overcome the strong nuclear force, making the nucleus unstable
• Alpha decay


  The process where a heavy nucleus emits a helium nucleus to become more stable
• The energy released during alpha decay comes out as the kinetic energy of the alpha particle and the recoil of the daughter nucleus
• Radioactive heating from alpha decay is a major source of heat in the Earth's core
• Most of the helium on Earth comes from the radioactive decay of elements inside the Earth
• Predicting the daughter nucleus after alpha decay

  1. Subtract 2 protons and 4 particles from the parent nucleus

  2. Look up the new atomic number on the periodic table to identify the element
• Ionization


  The process where alpha particles knock off electrons from atoms, creating positive ions and free electrons
• Highly ionizing radiation


  Alpha particles have high ionization power but low penetration power, they can be easily stopped by a piece of paper
• Smoke detectors use americium-241, a radioisotope that undergoes alpha decay, to detect smoke by sensing disruptions in the ionization current
• Opening a smoke detector to examine the americium source can be dangerous as it may lead to ingesting radioactive neptunium-237