Ionizing Radiation

Ionizing radiation may exist in the form of a high-energy photon or charged particles. When ionizing radiation passes through matter, some of the energy is absorbed and electrons are knocked out of atoms. This creates a trail of positive ions.

ionizing radiation
Ionizing side of the electromagnetic spectrum.

In living organisms this residual energy can be damaging to tissue, cellular processes, or DNA, especially if received in large amounts within a short period.  This is the main mechanism by which ionizing radiation can cause immediate harm or long-term illness (e.g. cancer).  However, at levels of exposure associated with natural and man-made radiation sources in the environment around us, our bodies are generally able to deal with the residual energy in a similar manner that they have adapted to deal with environmental levels of chemical and biological toxins.

X-rays and gamma rays have large amounts of energy and can ionize atoms in most types of matter. Although the atmosphere surrounding the Earth blocks most of the x-rays and gamma rays emitted by the Sun some do manage to get through.  On the other hand the atmosphere itself is also a significant source of ionizing radiation: when cosmic rays (mostly protons) interact with the upper atmosphere they create secondary x-rays and subatomic particles, such as muons, which contribute to our background radiation exposure.

Geiger counter
Geiger counters can detect ionizing radiation.

As mentioned earlier, ionizing radiation can exist in the form of moving particles. When radioactive elements and isotopes decay, they eject particles. These particles include photons, alpha particles, beta particles and neutrinos. Because ionizing radiation cannot be detected by our senses, we cannot see, smell or taste it. To detect ionizing radiation we must use special devices such as Geiger-Mϋller counters (often referred to as simply “Geiger counters”), dosimeters or cloud chambers.

Nuclear Radiation

While non-ionizing radiation and x-rays are a result of electron transitions in atoms or molecules, there are three forms of ionizing radiation that are a result of activity within the nucleus of an atom.  These forms of nuclear radiation are alpha particles (α-particles), beta particles (β-particles) and gamma rays (γ-rays).

Alpha particles are heavy positively charged particles made up of two protons and two neutrons.  They are essentially a helium nucleus and are thus represented in a nuclear equation by either α or n1.  See the Alpha Decay page for more information on alpha particles.

Beta particles come in two forms: n2 and n3n3 particles are just electrons that have been ejected from the nucleus.  This is a result of sub-nuclear reactions that result in a neutron decaying to a proton.  The electron is needed to conserve charge and comes from the nucleus.  It is not an orbital electron.  n2particles are positrons ejected from the nucleus when a proton decays to a neutron.  A positron is an anti-particle that is similar in nearly all respects to an electron, but has a positive charge.  See the Beta Decay page for more information on beta particles.

Gamma rays are photons of high energy electromagnetic radiation (light).  Gamma rays generally have the highest frequency and shortest wavelengths in the electromagnetic spectrum.  There is some overlap in the frequencies of gamma rays and x-rays; however, x-rays are formed from electron transitions while gamma rays are formed from nuclear transitions.  See the Gamma Rays page for more information on gamma rays.