Radioactive vs irradiated

A radioactive object and an irradiated object are very different things. Although they both involve radiation, the way that this radiation interacts with the object is what makes a radioactive substance different than a substance or object that has been irradiated.

Radioactive Objects

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A radioactive substance is one that releases radiation from its surface, potentially through some radioactive decay process—such as alpha decay, beta decay, or gamma decay. The radiation that is released is energy that doesn't require a medium to travel and is released in small, quantized packets of energy known as photons. Radioactive objects can be dangerous to human health or not, depending on their levels of radioactivity. Many common objects, even bananas and smoke detectors, are radioactive at levels that are not harmful. However if the levels of radiation from the object become too great there can be associated health risks.

Irradiated Objects

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An irradiated substance is one that has had radiated energy interact with it, generally the radiation has simply fallen on the surface.[1] When radiation is incident on a surface, it is either absorbed or reflected depending on the properties of the surface. Blackbodies absorb all the radiation incident on the surface while other objects reflect to some degree.


Figure 1. A radioactive substance has the ability to emit radiation—an irradiated substance can absorb and/or reflect. [2]

Essentially, the main difference between the two is how radiation is connected to the object being discussed. A radioactive object is the source of some radiation, while an irradiated object is some object that has had some radiation interact with it.[1]

An analogy may be helpful, an irradiated object is like a book with light shining on it, while a radioactive object is like a light bulb. Radioactive objects give off the radiation that is produced from nuclear processes inside of them. Being irradiated can affect the properties of the object (like killing germs in food) but doesn't make the object radioactive.[3]

Additionally, irradiated objects and radioactive objects tend to serve different purposes. Food is generally irradiated to control spoilage and eliminate food-borne pathogens and bacteria.[4] Conversely, radioactive isotopes are used extensively in the medical field. As well, radioactive isotopes are used in the nuclear fission reactors that are used to generate electricity worldwide.

For Further Reading


  1. 1.0 1.1 Difference Between. (July 8, 2015). Difference Between Radiation and Irradiation [Online]. Available:
  2. Made internelly by a member of the Energy Education team.
  3. Thanks to Dr. Anna Harding for this excellent analogy, private communication with Dr. Jason Donev in April of 2011.
  4. EPA. (July 8, 2015). Food Irradiation [Online]. Available: