Radioactivity (Radioactive decacy), its types and properties of different radioactive rays

  • The naturally occurring elements like Uranium, Polonium, Radium etc. constantly undergo a spontaneous change with the emission of different radioactive rays. This phenomenon of emission of strong radioactive rays like α, β, ϒ and X-rays by such elements is called radioactivity.
  • The substances which exhibit the properties of radioactivity are called radioactive elements.

Types of radioactivity:

  • Natural radioactivity:
    • Nuclear reactions which occur spontaneously in nature lead to natural radioactivity.
    • The heavier radioactive elements in Uranium series, Thorium series and Actinium series decay naturally through a number of unstable nuclei emitting radiation, called natural radiation.
  • Artificial radioactivity:
    • Not all nuclear reactions are spontaneous.
    • Some of the nuclear reactions only occur when stable isotopes are bombarded with particles such as neutrons and then they release radiation, called artificial radiation.
    • This property of some elements to emit radiation is called artificial radioactivity.
    • Transuranium elements (Neptunium, Lawrencium etc.) with atomic numbers more than 92 (Uranium), which have been artificially made, emit such radiation.

Types of radioactive rays and their properties;

There are different types of radioactive rays emitted from radioactive substances, but the frequently encountered are the following 3 types:

  1. Alpha rays:
    • α-radiation is a heavy, very short-range particle.
    • They have a charge of 3.202 x 10-19 coulomb (i.e. twice the charge of electron). Hence, they are actually doubly charged He nucleus.
    • The velocity of α-particles ranges from 1/10 to 1/100 of the velocity of light.
    • They produce intense ionization in the gas through which they pass. They have the strongest ionization power (about 100 times ionization power than β-particles and 10,000 times than ϒ-particles).
    • They have less or no penetrating power. They can’t penetrate human skin, clothing or other materials.
    • α- radiation emitting materials if inhaled, swallowed, or absorbed through open wounds can be harmful to humans.
    • The presence of α-radiation can be detected by thin-window Geiger-Mueller (GM) probe.
    • α- radiation cannot travel for a long distance in air and not hazardous.
    • They are deflected by electric and magnetic field.
    • Radium, Radon, Uranium, Thorium etc. emit α- radiation.
  1. Beta rays
    • Beta radiation carries a light and short-range particle (β-particle) with a charge of 1.6 x 10-19C (equal to the charge of an electron). Hence, it is actually an ejected electron.
    • They are fast moving radiation (several feet in air). The velocity of β-particles ranges from 33% to 99% of velocity of light.
    • They are moderately penetrating. They can penetrate our skin up to the germinal layer. Prolonged exposure to high level β-radiation can cause skin injury.
    • They can also ionize the gas through which they pass and are also deflected by electric and magnetic fields.
    • Most high energy and moderately penetrating β-radiation emitting substances can be detected with the help of a thin-window GM and a survey instrument. However, low-energy and poorly penetrating radiation emitted by tritium, carbon-14, and sulfur-35, may be difficult or impossible to detect.
    • Clothing provides some protection against beta radiation.
    • Strontium-90, carbon-14, tritium, and sulfur-35 are some β-radiation emitting substances.
  2. Gamma rays:
    • ϒ-radiation doesn’t carry any charged particles hence, it is charge less. But they are the most energetic of all the radioactive rays.
    • They travel in a straight line with the velocity of light in vacuum and travel longer up to many feet in air.
    • They are highly penetrating electromagnetic radiation and can penetrate through many inches in solid substances including human tissues. Hence, they are called penetrating radiation.
    • They have the least ionization power of all the radioactive radiations.
    • They are hazardous to our body. Hence, dense and thick materials are needed for shielding and protection from gamma radiation.
    • Survey meters with a sodium iodide detector probe can easily detect Gamma radiation.
    • They are not deflected by electric or magnetic fields, since they are electromagnetic waves.
    • They are used in medicine (radiotherapy), industry (sterilization and disinfection) and the nuclear industry.
    • Iodine-131, cesium-137, cobalt-60, radium-226, technetium-99m etc. emit ϒ-radiation.

Radioactivity (Radioactive decacy), its types and properties of different radioactive rays