Nuclear Power Plant Isar, Germany

Spent nuclear fuel pool

Turbine of a nuclear plant

What Is An Isotope?

Isotopes are atoms whose atomic nuclei have the same number of protons but different numbers of neutrons. Not all atoms of the same element are identical and each of these varieties corresponds to a different isotope.

What is an isotope?

Each isotope of the same element has the same atomic number (Z) but each has a different mass number (A). The atomic number corresponds to the number of protons in the atomic nucleus of the atom. The mass number corresponds to the sum of neutrons and protons in the nucleus. This means that the different isotopes of the same atom differ from each other only by the number of neutrons.

periodic table of elements

Each atom can have any number of neutrons. The different combinations of neutrons and protons imply differences in the cohesion forces of the nuclei of the isotopes. Thus, although they may have any number of neutrons, there are some preferred proton and neutron combinations in the different isotopes.

Light isotopes (with few protons and neutrons) tend to equal the number of neutrons and protons, while heavy isotopes tend to have more neutrons than protons.

That each isotope of the same element has the same atomic number means that they have the same number of protons in the atomic nucleus. Atoms of the same element have the same number of protons and electrons but can have different numbers of neutrons.

Are the isotopes of natural origin?

The elements that can be found in nature can be configured in a great variety of different isotopes. The mass that appears in the periodic table of the elements is the average of all the masses of all the isotopes that can be found naturally.

An example of a natural isotope is hydrogen. Hydrogen has three natural isotopes, protium, deuterium, and tritium. These isotopes are used as fuel for nuclear fusion. In the nuclear weapons aspect, they are the basic elements that make up the hydrogen bomb.

Most natural elements are made up of various isotopes that can only be separated by physical procedures (diffusion, centrifugation, mass spectrometry, fractional distillation, and electrolysis).

How are isotopes classified?

Isotopes can be of two types:

  • Stable isotopes
  • Unstable isotopes

Stable isotopes have a half-life of the order of 3 billion years. On the other hand, unstable isotopes are radioactive. Unstable elements emit radiation and become other isotopes or elements. 

What are unstable isotopes?

Unstable atoms are radioactive atoms: their nuclei change or disintegrate, emitting radiation. Isotopes with or without neutron can be found. These atoms may exist for some time, but they are unstable.

This instability is precisely what is sought in the nuclear fuel used in nuclear power plants. Being unstable, it is much easier to generate nuclear fission reactions.

Usually what makes an isotope unstable is the large nucleus. If a nucleus becomes large enough from the number of neutrons it will be unstable and will attempt to eject its neutrons and / or protons to achieve stability. Neutron / proton emission as well as gamma radiation is radioactivity.

What applications do unstable isotopes have?

Unstable isotopes have many possible applications in our lives.

  • First, an isotope of cobalt is used in medicine to stop the spread of cancer.
  • Radioactive isotopes can be used as tracers in patients to monitor various internal processes. An isotope of iodine has been used to find brain tumors. 
  • In addition to nuclear medicine, unstable isotopes in industry can measure the thickness of metal or use it to generate electricity, such as sources of uranium or plutonium.
  • Part of the electricity we consume daily is generated in a nuclear power plant. In nuclear power plants, unstable isotopes of uranium are worked to generate fission reactions in the nuclear reactor core.
  • For dating. In archeology, for example, it is very common to use carbon 14 to establish the dating of different elements.

However, these unstable isotopes can be dangerous in high doses and difficult to store, making it extremely important to limit or completely discourage contact with these isotopes. Certain isotopes can also have very high energies and release large amounts of nuclear energy when they decompose, creating a possibly destructive hazard.

How are the different isotopes of an element represented?

Uranium is present in a wide variety of isotopesThere are two ways of representing them: according to scientific notation and according to symbolic notation.

  • Scientific notation of isotopes: Isotopes are identified by the name of the chemical element followed by the number of protons and neutrons in the isotope. For example, the three most common isotopes in uranium used as nuclear fuel would be represented like this: U-235, U-235 and U-238
  • Symbolic notation of isotopes: the number of nucleons (protons and neutrons) is denoted as a prefix superscript of the chemical symbol. In the case of the three previous isotopes of uranium it would be 234 U, 235 U and 238 U

Who discovered the isotopes?

The existence of isotopes was discovered as a result of the study on natural radioactive substances. The name of isotope was proposed by Frederick Soddy in 1911. Soddy verified the equality of its chemical properties.

Rutherford and Soody realized that the abnormal behavior of radioactive elements was due to the fact that they transformed into other elements and produced alpha, beta and gamma radiation.

Frederick Soddy received the Nobel Prize in Chemistry in 1921 for his work on isotopes and radioactivity.


Published: January 2, 2013
Last review: March 27, 2020