Ionizing Radiation: Definition, Sources, Types, and Examples

Ionizing radiation is the subatomic particles or electromagnetic waves which have enough energy to ionize atoms or molecules by detaching electrons from them.

• High-energy ultraviolet rays, X-rays, and Gamma rays of the electromagnetic spectrum are ionizing radiation.
• Low-energy ultraviolet rays, visible light, infrared, radio, and microwave waves are examples of non-ionizing radiation.
• Alpha particles, beta particles, and neutrons are ionizing subatomic particles created by radioactive decay.
• The energy of ionizing radiation ranges between 10 electronvolts to 33 electronvolts.
• Ionizing radiation is not seen by human eyes, so instruments like Geiger counters are used to detect and measure ionizing radiation.
• Very high-energy particles of ionizing radiation can be visible to humans visible effects.
• Ionizing radiation has several uses such as medicine, research, nuclear power plant, and industrial manufacturing.
• Cell damage and organ damage can result from prolonged exposure to ionizing radiation.

Key Terms: Electromagnetic waves, Radiation, Atoms, UV- rays, Radioactive decay, X-rays, Alpha rays, Radioactivity, Positrons, Gamma rays

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Introduction to Ionizing Radiation

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Atoms are the building block of all matter and it consists of a nucleus surrounded by electrons which revolve around the nucleus. Nuclei contain protons and neutrons together called nucleons.

• The atomic number of a chemical element is determined by the number of protons and the number of neutrons determines the isotope.
• Some isotopes are unstable and to become stable they continuously release energy (known as decay).
• The unstable atoms are radioactive and continuously released in the form of radiation.
• If the energy of the radiation is enough to detach electrons or ionize other atoms, then the radiation is referred to as Ionising radiation.
• Alpha particles, beta particles, and neutrons are high-energy ionizing subatomic particles created by radioactive decay.
• High-energy ultraviolet rays, X-rays, and Gamma rays of the electromagnetic spectrum are ionizing radiation.
• Low-energy ultraviolet rays, visible light, infrared, radio, and microwave waves are the types of non-ionizing radiation.
• Radionuclides (or radioisotopes) are unstable, radioactive elements that will gradually lose their radioactivity through radioactive decay as they decay into a more stable form over time.

Ionizing Radiation

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Sources of Ionizing Radiation

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People are always exposed to natural radiation sources as well as human-made radiation sources. Some natural and man-made sources of ionizing radiation are discussed below:

• Radioactive materials and radiation-generating machines are the sources of ionizing radiation. 
• Radioactive materials occur naturally such as radium and uranium and can be manmade in an accelerator or reactor. 
• Medical X-ray machines produce radiation-generating machines that produce ionizing radiation electronically.

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Types of Ionizing Radiation

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There are major five types of Ionizing radiation. These are

1. Alpha Particles
2. Beta Particles
3. Positrons
4. Gamma Rays
5. X Rays

Alpha Particles (α-partciles)

An alpha particle is equivalent to a helium nucleus (₂He⁴) i.e. doubly ionized helium atom consisting of 2 protons and 2 neutrons.

• They have a positive charge equal to +2e.
• They are emitted with velocities ranging between 1.4 x 10⁷ m/s to 2.2 x 10⁷ m/s.
• Radionuclides that emit alpha particles are Uranium-238, Radon-222, Thorium-230, etc. 

Beta Particles (β-particles)

A beta particle is comparable to a fast-moving electron.

• They have a negative charge equal to the charge of an electron.
• They are emitted with a velocity of about 2.97 x 10⁸ m/s.
• Some radionuclides that emit beta particles are Strontium-90 (Sr-90), Phosphorus-32, Carbon-14, etc.

Positrons

Positrons are fast-moving electrons emitted from the nucleus of various radionuclides.

• They have a positive charge of magnitude equal to the charge of an electron.
• Positions can be emitted by unstable atoms with a low neutron-to-proton ratio.
• An example of a positron-emitting radionuclide is Fluorine-18 (F-18) which is used as positron emission tomography (PET) scanning in medical facilities.

Gamma Rays

Gamma rays are high energy packets of electromagnetic radiation i.e. high energy photons.

• Gamma rays can travel great distances at very high speed and it is the pure form of energy.
• They have no charge.
• Some radionuclides that emit gamma rays are Cesium-137, Iodine-131, Cobalt-60, etc.

X Rays

These are the High-energy electromagnetic waves or photons emitted from outside the nucleus.

• The basic difference between X-rays and Gamma rays is that the X-rays are emitted from outside the nucleus and Gamma rays are emitted from inside the nucleus.
• Some radionuclides that emit X-rays are Iron-55, Iodine-125, etc. Some machines containing an X-ray tube also produce X-rays.

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Examples of Ionizing Radiation

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Ionizing radiation can be natural or man-made.

• A few examples of natural ionizing radiation are zirconium, radioactive minerals, metal mining, cosmic rays from the sun and stars, radioactive soil, metal smelting, and radioactive rocks.
• A few examples of man-made ionizing radiation are nuclear reactors, x-rays, tomography, radiotherapy, and a few other medical testing equipment.

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Things to Remember

• If the energy of the radiation from unstable isotopes is enough to detach electrons or ionize other atoms, then the radiation is referred to as Ionising radiation.
• Radioactive materials and radiation-generating machines are the sources of ionizing radiation.
• Some examples of Ionising radiation are X-rays, tomography, radiotherapy, radioactive rocks, cosmic rays from the sun and stars, etc.
• Alpha particles are emitted with velocities ranging between 1.4 x 10⁷ m/s to 2.2 x 10⁷ m/s.
• The effects of ionizing radiation on biological tissue are understood by knowing that ionizing radiation affects molecules within cells. Especially DNA molecules.

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