Radioactivity refers to the particles which are emitted from nuclei as a result of nuclear instability. Radioactivity, property exhibited by certain types of matter of emitting energy and subatomic particles spontaneously. It is, in essence, an attribute of individual atomic nuclei.


Radioactive decay, also known as nuclear decay or radioactivity, is the process by which the nucleus of an unstable atom loses energy by emitting radiation, including alpha particles, beta particles, gamma rays and conversion electrons.

Key Point: A material that spontaneously emits such radiation is considered radioactive.

A radioactive atom is one that spontaneously emits energetic particles or waves (known as radiation). This radiation is emitted when an unstable (i.e. radioactive) nucleus transforms to some other nucleus or energy level. Imagine a big ball made of magnets that’s spinning really fast. Sometimes a few pieces of the magnet will shoot out and hit the wall. That’s kind of what radiation is like. As it applies to nuclear energy, many materials created during the operation of a reactor are unstable. As they decay over varying lengths of time (from microseconds to hundreds of thousands of years), they emit energetic particles or waves. The energy carried by this radiation is often sufficient to cause damage to biological cells and is therefore a health risk. Thus, radiation is the primary cause of safety concerns related to nuclear energy.



1. Smoke detectors

Smoke detectors make use of the isotope Americium-241. This isotope emits alpha-particles at energies up to 5.4 MeV. The energetic alpha particles are used to ionize air. Once the air is ionized, a small current runs through it. When smoke enters the chamber, the current experiences an increase in resistance and a circuit sounds the alarm.

2. Coal-burning power plants

Coal is an impure fuel, and it usually contains 1.3 ppm of uranium and 3.4 ppm of thorium (not to mention arsenic, mercury, and sulfur). When coal burns, these isotopes are emitted into the atmosphere, where they enter our ecosystem. This leads to the astounding fact that the population effective dose equivalent from coal plants is 100 times that from nuclear plants.

3. Nuclear weapon detonations

The hundreds of atmospheric nuclear weapons tests that occurred before they were banned by the 1963 Limited Test Ban Treaty left long-lived radioisotopes in the atmosphere. Some of these are still in the atmosphere and account for some of our daily dose.

4. Radon gas

This natural occurring gas comes from soil and is found throughout the world. It emits alpha particles, and can therefore damage DNA and lead to cancer if inhaled. The EPA recommends you check your house for radon gas.

5. Cosmic rays

Cosmic rays are energetic particles that originate outside of earth, in the sun, distant stars, galaxies, and supernovae. Most of these are protons. The atmosphere shields us from most cosmic rays, but during air travel, one will accumulate much higher dose.

Note: The first three are Man made, while the last two are Natural.