25.1 Radioactivity

• Radioactive substances emit different types of radiation; alpha, beta and gamma. All three are described as ionizing radiations because they can ionize atoms by removing some of their electrons, leaving positive ions.
• A cloud chamber can be used to detect the presence of radiation; it contains air saturated with vapor at a very low temperature. When the air molecules are ionized, liquid condenses on the walls of the chamber.
• Beta radiation consists of fast-moving electrons or positrons.
• A beam of particles projected at a uniform electric field provided by two oppositely charged parallel plates can distinguish the different types of radiation. The negative beta-minus particles (electrons) are deflected towards the positive plate. The positive alpha and beta-plus particles particles are deflected towards the negative plate. Alpha particles are deflected less than beta particles because of their greater mass. Gamma rays are not deflected; they are uncharged.
• A geiger-muller tube is a device that detects the presence of radioactive decay, and produces a count or click.
• The large mass and charge of alpha particles mean they interact with surrounding particles to produce strong ionization and have a short range. A thin sheet of paper completely absorbs them.
• The small mass and charge of beta particles make them less ionizing than alpha particles, they have a greater range. It takes a few millimeters of aluminum to absorb them.
• Gamma rays have no charge, and this makes them less ionizing than beta particles, they have the greatest range; a few centimeters of lead to absorb it.
• All types of radiation cause ionization, which means they can damage living cells; their stored in lead-lined storage storage containers.