Nuclear Power Plant Isar, Germany

Spent nuclear fuel pool

Turbine of a nuclear plant

What Is Radioactivity? Definition Of Nuclear Decay

What is radioactivity? Definition of nuclear decay

Radioactivity is the spontaneous emission of particles or radiation, or both at the same time. These particles and radiation come from the decay of certain nuclides that form them. They disintegrate due to a fix in their internal structure.

The particles can be alpha, beta, or neutron. Radiations can be gamma and capture K.

Radioactive decay occurs in unstable atomic nuclei. That is, those that do not have enough binding energy to hold the nucleus together.

The decaying nucleus is called the parent. The process produces at least one daughter nuclide.

The decay is a nuclear transmutation resulting in a daughter containing a different number of protons or neutrons (or both). The exception of this rule is for gamma decay or internal conversion from a nuclear excited state.

Radiation was discovered by Antoine Henri Becquerel and Marie Curie.

There are two types of radioactivity:

  • Natural. Radioactive material is already radioactive in its natural state.
  • Artificial. It has been induced by humans.

What is natural radioactivity?

Natural radioactivity is nuclear decay naturally occurring due to chains of natural radioactive elements. It is constantly present in the environment.

Natural radioactivity can also be increased in a focus by:

  • Natural causes. For example, carbon-14 is a radioactive nuclide. It is constantly produced in Earth's upper atmosphere due to interactions between cosmic rays and nitrogen.
  • Indirect human causes. For example an excavation in the ground to make the foundations of a building. Or the exploitation of nuclear energy in nuclear reactors.

What is artificial nuclear decay?

Artificial nuclear decay is all radioactivity or ionizing radiation of human origin. The only difference between natural radiation and artificial radiation is where they come from. The effects of both radiations are identical.

In both cases, the directly ionizing radiation is alpha radiation and beta decay formed by electrons.

Examples of artificial radiation sources:

Artificial radiation sources may produce nuclear waste.

Emissions types

Among the light elements, the most frequent radiations are:

  • Beta-b radiation, which are electrons from the nucleus.
  • Beta b + radiation, which are positrons from the nucleus positively charged.
  • Gamma rays (g).
  • Electronic capture (K decays).
  • Alpha radiation is characteristic of heavy elements.

Each type of radioactive emission has different penetrating power in matter and different ionization energy. They can cause serious damage to living things.

Alpha particles

Alpha (α) particles are a form of ionizing high-energy corpuscular radiation. They are also called or alpha rays. They have little ability to penetrate tissues because they are large. They consist of two protons and two neutrons held together by a strong force.

In an alpha decay, an atomic nucleus emits an alpha particle

Alpha rays, due to their electrical charge, interact strongly with matter. They are easily absorbed by the materials. They can travel only a few centimeters in the air.

How do they affect humans?

They can be absorbed by the outermost layers of human skin. Therefore, they are therefore not toxic unless the source is inhaled or ingested. In this case, the damage would instead be greater than that caused by any other ionizing radiation.

At high doses all the typical symptoms of radiation poisoning appear.

Beta particles

Beta radiation is a form of ionizing radiation emitted by certain types of radioactive nuclei.

During beta decay, when a proton inside a nucleus is converted into a neutron emit a positron.

Gamma rays

Gamma rays are electromagnetic radiation produced by radioactivity. They stabilize the nucleus without changing its proton content. They penetrate deeper than a or beta radiation, but are less ionizing.

When an excited nucleus emits gamma radiation, neither its mass nor its atomic number varies. It only loses a certain amount of energy.

The daughter nuclei are produced from alpha and/or beta decay. Alpha or beta decay are generally excited. They emit a gamma-ray photon.

Effects in humans

Gamma radiation can cause serious damage to the nucleus of cells. So that, they are used to sterilize medical equipment and food.

What are radioactive nuclei?

A radionuclide is the set of radioactive nuclei of the same species.

All the radioactive nuclei that make up a radionuclide have a well-defined radioactivity that identifies them. In the same way that a type of chemical reaction identifies the elements that participate.

What is radioactivity?

Radioactivity is a statistical phenomenon. The important is the behavior of a set of nuclei of the radioactive substance of the same species. The radioactive constant λ is the chance of decay of a nucleus per unit time.

Common sources of radiation

There are three different types:

“Man-made” radiation

  • Smoke detectors. Smoke detectors make use isotopes.
  • Coal-burning power plants. When coal burns, these isotopes are emitted into the atmosphere.
  • Nuclear weapon detonations. The hundreds of atmospheric nuclear weapons tests that occurred left long-lived radioisotopes in the atmosphere. Some of these are still in the atmosphere and account for some of our daily dose.

Natural radiation

Radon gas. This naturally occurring gas comes from the soil. It emits alpha particles, and can therefore damage DNA and lead to cancer if inhaled.

Cosmic rays

Cosmic rays are particles that originate outside of earth. Ther are highly energetic. In the sun or in distant stars, galaxies, and supernovae. Most of these are protons

Origins of cosmic rays:

  • Outside our galaxy.
  • In our galaxy.
  • In the sun.
  • On interplanetary space.



    Published: December 10, 2009
    Last review: May 15, 2020