Radiation

Radiation is simply the transmission of energy from a source via waves or particles.

There are many kinds of radiation that move in waves, most of them very familiar to you, like radio waves, visible light, and x-rays. They are all part of the electromagnetic spectrum.

Radiation can also be described as non-ionizing or ionizing.

Non-ionizing radiation has enough energy to excite atoms, making them move more rapidly. Microwave ovens work by exciting water molecules, creating friction. The friction creates heat, and the heat warms the food. Other examples of non-ionizing sources include radio transmissions, cell phones, and visible light.

Ionizing radiation has enough energy to remove electrons from their orbits, creating ions. Examples of ionizing sources are high-level ultraviolet light, X-rays, and gamma rays.

Learn About Beneficial Uses of Radiation

Learn About Radiation Exposure

Radioactive decay

Ionizing radiation happens when an unstable atom (a radioactive isotope of an element) emits particles or waves of particles to become more stable. This process is called radioactive decay.

Not all of the atoms of a radioactive isotope decay at the same time. Instead, the atoms decay at a rate that is characteristic to the isotope. The rate of decay is a fixed rate called a half-life.

The half-life of a radioactive isotope refers to the amount of time required for half of a quantity of a radioactive isotope to decay. For example, carbon-14 has a half-life of 5730 years, which means that if you take one gram of carbon-14, half of it will decay in 5730 years. Different isotopes have different half-lives.

Radioactive decay is random; we can't tell which atoms in an isotope sample will decay. But, it is also predictable and exponential, so we can determine how long it will take for a sample to completely decay based on its half-life.

There are four basic types of ionizing radiation--alpha, beta, gamma, and neutron--and each has unique properties.

Alpha radiation happens when the unstable atom emits two protons and two neutrons—basically a helium nucleus. The original atom, with fewer protons and neutrons, becomes a different element.

Compared to other forms of ionizing radiation, alpha particles are large and heavy. They can’t travel very far, so they are useful in things like smoke detectors. They can be stopped by a piece of paper, your skin, or even just a few inches of air.

Beta radiation

Beta radiation occurs when an atom decays by giving off a high-energy, high-speed particle that has a negative or positive charge. These “beta” particles are both smaller and more energetic than alpha particles. There are two types of beta decay. When a negatively charged particle is emitted from the nucleus, it is called beta minus decay. The negative beta particle is also called an electron, but it originates from the nucleus, not the electron cloud surrounding the atom. When a positively charged particle is emitted from the nucleus, it is called beta plus decay or positron emission, because the positively charged particles are called positrons. They have the same mass as electrons.

Beta minus decay happens when an atom has more neutrons than protons. To gain stability, a neutron becomes a proton and an electron. The proton stays in the nucleus, while the electron (beta minus particle) is emitted. Because the atom gains a proton and loses a neutron, its atomic number increases by one. The mass number stays the same because the number of nucleons stays the same.

Beta plus decay (positron emission) happens when an atom has more protons than neutrons. To become more stable, a proton becomes a neutron, and a positron is emitted. Because the nucleus loses a proton and gains a neutron, its atomic number decreases by one and the atom becomes a different element. The atom still has the same number of nucleons, though, so the mass number stays the same.

Gamma radiation and x-rays, are high-energy waves that can travel great distances at the speed of light. Both can penetrate deeply into matter.

X-rays are stopped by dense materials like bone, tumors, or lead. This makes them useful for medical diagnosis.

Gamma rays can penetrate further with higher energy. Gamma radiation can be used to precisely target and eliminate tumors; it also has a number of uses in industry, agriculture, pest-control, and more. Gamma rays be stopped by several inches of lead.

Neutron radiation is created as a result of fission reactions and happens in nuclear reactors. Neutrons are extremely high energy, so need many feet of dense materials like water or concrete to stop them. Neutron radiation can make other materials radioactive and is used to create the radioisotopes used in medical treatments.