Isotopes: Examples, Definition, Types and Uses

Image showing the three isotopes of hydrogen with different number of neutron
Examples of hydrogen isotopes. Source: WorldAtlas

Isotopes are atoms of the same elements with the same atomic number but different mass numbers. These are not different types of elements. What distinguishes them is the difference in their constituent minerals.

Every element is made up of small components called atoms. These atoms are invisible to the naked eye and are composed of two parts. These are; the nucleus and the electron.

The electrons are negatively charged bodies of the atom. They move around the nucleus in orbits and are bonded by electromagnetic forces. There are several electrons in an atom.

The nucleus of the atom contains two particles; protons and neutrons. Protons are positively charged particles within the nucleus of the atom. Neutrons, on the other hand, are electrically neutral particles. They have similar dimensions as the proton but weigh more. Because of their combined weight, the bulk of the weight of the atom resides more in the nucleus.

The neutrality of an element is affected when there is a change in the number of either the proton or the electron. This is because the positive charges on protons balance the negative charges on electrons to give an electrically neutral atom. If the protons are more than the number of electrons, the element would be positively charged. And conversely, if the electrons are more than protons, the element would be negatively charged.

Atoms with charges are called ions. Those with positive charges are called cations while those that are negatively charged are referred to as anions.

Table of Contents

How do isotopes occur?

Isotopes occur, not because of the charges on the elements but from a variation in the proton to neutron ratio. The number of the proton or the electron in an atom is referred to as the atomic number. On the other hand, the total number of protons and neutrons in the nucleus is the mass number of the element.

Mass numbers are an indication of the weight of the nucleus and the element as a whole. It is mostly influenced by the weight of the neutron. Because the neutron weighs more, if the number of neutrons in an atom increases, the weight of the atom increases also. But if the number of neutrons is reduced, the mass number and the weight of the atom would be reduced.

Recall that the protons in an atom are the same number as the electron. Hence, when differences occur, they can be identified by subtracting the atomic number from the mass number of the element.

Asides the changes in the mass numbers, isotopes do not differ much from each other. They still retain the same atomic numbers. Therefore, they have similar physical properties.

Isotopes could occur naturally or could be man-made. These man-made isotopes are synthesized in the laboratory.

Types of Isotopes

There are two main types of isotopes. These types are divided based on their occurrences and stability.

Stable isotopes

Isotopes are known to be stable if they do not undergo any radioactive decay. Many times, this is possible because the number of protons and neutrons in the nucleus is the same. If the number of neutrons becomes more or less than that of the proton, the atom loses its stability.

Most of the stable isotopes are found as naturally occurring. These can be easily detected using any chemical or spectroscopic method.

Stable isotopes do not emit any radiation nor do they pose a major risk to health for the seemingly obvious reason that they are stable. For those that are hazardous, their toxicity does not hinge on their isotopic nature but rather on the chemical they form

Some examples of stable isotopes include oxygen-16 and oxygen-18, hydrogen-2 and hydrogen-1, nitrogen-15, and nitrogen-14. Tin holds the record of having the most stable isotopes. Ten of the thirty isotopes of tin are stable. Although there are three potentially radioactive isotopes amongst them, none of them have been observed to decay.

Unstable isotopes

Unstable isotopes unlike stable ones have different numbers of protons and neutrons in their nucleus. The number of neutrons could be more or less than the number of protons. In trying to attain stability, they could lose or gain electrons or protons. Unstable isotopes could also be called radioactive isotopes or radioactive nuclides.

Radioactive nuclides are thus constantly changing. This process of gaining stability by the unstable nuclides is referred to as radioactive decay. Radioactive decay often results in the formation of another element with the release of radioactive particles and energy. Some of the radioactive particles released are; Alpha (α), beta (β), and gamma (γ)

Many of the radioactive nuclides are less abundant in nature as most of them are created in the laboratory. They can be detected using external methods such as scintillators and gas chambers. Special handling methods are required for many of these nuclides because their unstable nature poses health and environmental risks.

Examples of radioisotopes include; isotopes of uranium, thorium.

Radioactive Particles

Several radioactive particles are released from radioactive isotopes. The release of these particles is accompanied by energy. Each of these particles has unique characteristics such as how far they can penetrate, their wavelengths, and their intensities. There are three main radioactive particles; alpha particle (α), beta particle (β), and gamma radiations (γ)

Alpha particles (α)

The alpha particles are one of the most common radioactive particles released by radioactive nuclides. These particles are positively charged and are spontaneously emitted by both natural and man-made elements. They have a mass number of 4 and atomic number 2 making them similar to the element helium.

Alpha particles have a short penetration distance. Hence, they can be stopped by a sheet of paper. Their ionization power is high hence they can ionize several atoms over a short distance.

Like many radioactive particles, these particles can be dangerous to health and require to be handled with care. Therefore, a major precaution applied when handling alpha particles is the use of rubber gloves.

These have several uses of alpha particles such as smoke detectors in buildings.

Beta particles (β)

Beta particles are negatively radioactive particles. Their weight is more than that of alpha particles. Emissions of beta particles are denoted with the loss of an electron. These particles are only emitted from natural elements such as carbon-14, hydrogen-3.

These particles can penetrate much farther than alpha particles although their ionization power is lower than that of alpha particles.

Beta particles are used in the treatment of some eye diseases.

Gamma radiation (γ)

Gamma radiations do not bear any charge because they are electromagnetic radiations. They travel at the speed of light. Their penetration distance is the highest and their ionization power is the lowest. The energy within these particles is higher than those in the other radioactive types.

Can isotopes be created?

Many radioactive isotopes are as old as the earth. They were created with the earth and are referred to as long-lived radioactive isotopes. Common examples include; isotopes of thorium and uranium that are found naturally in the soil.

Some radioactive isotopes, however, can be created in the laboratory. These are made through many processes such as bombarding stable nuclei such as that of uranium with high-speed charged particles. Common examples of laboratory synthesized radioactive isotopes include; technetium-95 and promethium-146.

Another way radioisotopes occur is when they are released into the atmosphere through cosmic activities. These could be radiations emitted from stars or particles from dying or colliding stars.

Isotope Notations

Isotope notations could also be called nuclear notation. These are ways of writing isotopes and are easy ways to represent the mass and atomic numbers of the isotopes. With this, it is easy to determine how many neutrons and protons are in the nucleus of the atom.

Many times, isotopes are written just like other elements. First, a letter is written to denote the element. For instance, Carbon is denoted by the letter C, Potassium by K, and Uranium by U.

The letters or symbol of each element is got from its name on the periodic table of elements. Each element on the periodic table has a symbol unique from the others that identify it. These symbols are recognized internationally by the IUPAC

Next, you write the mass number as a superscript just in front of the element. The atomic number too is written in front of the element but as a subscript. This is the most common way of writing many elements. However, many isotopes are written using the hyphen notation.

In the hyphen notation, only the mass number is considered. A hyphen is drawn between the symbol of the element and the mass number. For example, Carbon with a mass number of 14 is written as carbon-14 while that with mass number 12 would be written as carbon-12.

What are common examples of Isotopes?

All elements have isotopes. Although some of them occur naturally, others are synthesized in the laboratory.

Isotopes of carbon are the commonest examples. There are 15 recognized isotopes of carbon; carbon-8 through carbon-22. Only carbon-12, carbon-13, and carbon-14 exist naturally. These all have the same atomic number of 6 but different numbers of neutrons hence different mass numbers.

Hydrogen has just one electron, one proton, and no neutron. Hence, it is written on the periodic table with atomic number 1 and mass number. When hydrogen occurs with a neutron, it gives rise to several isotopes of the element. There are three naturally occurring isotopes of hydrogen. These are hydrogen-1 called Protium, hydrogen-2 called Deuterium, and hydrogen-3 called Tritium.

Uranium also has three common isotopes; uranium-234, uranium-235, and uranium-238. These are well known for their radioactive properties. If left alone, these radioactive particles would decay or break down to another element. This decay process places special interest on all the isotopes of uranium and their derivatives.

Examples of Isotopes and their Uses

Both stable and unstable isotopes have found wide application in our daily lives. These areas include medicine, agriculture, and geology. The unstable isotopes especially have gained wide recognition because of their unstable nature and the risks they pose to health. Some of the uses of isotopes include;

Uses of Stable Isotopes

Stable isotopes have several uses such as;


Several stable nuclides such as copper, zinc, and molybdenum are very useful geologic tools. The field of geology that focuses on the use of isotopes is known as isotope geology.

  • Petroleum studies:

Carbon and hydrogen are the main constituents of organic matter. Other elements such as oxygen, nitrogen, and sulfur could also be obtained in varying quantities in these materials. These materials decompose over millions of years to forms petroleum.

In petroleum studies, the stable isotopes of these elements are used to determine the maturity of oil wells and gas fields. They are also used to evaluate the source of rocks, their environment of deposition as well as the alterations that have occurred.

  • Paleontological studies:

Stable isotopes of oxygen give an idea into ancient marine environments. Thus, it is possible to understand the prevailing conditions in these environments. It is also important in tying occurrences on the stratigraphic column.

Using the stable isotopes of carbon, nitrogen, and oxygen, it is possible to reconstruct paleoclimate and follow the changes that happened within specific times.

  • Geochemistry:

Minerals are made up of different elements. Stable nuclides do not decay hence can serve as guides in understanding the mineral source especially for metals. Through the ratios of isotopes of hydrogen, carbon, oxygen, and sulfur, we gain an understanding of the source, the interaction of the mineralizing fluid as it traveled, its ore, and even the gangue.


Archaeologists employ stable isotopes to decipher the habits of some past organisms. Often times, these animals such as deep-sea creatures and nocturnal animals cannot be easily studied hence studies are carried out when they die.

Stable isotopes such as carbon-12 and carbon-13 can give information about the feeding habit of the organism. This could be done indirectly on some parts of the organism such as the hair, claws, and nails.

Marine Studies

Stable isotopes of carbon (carbon-13) and that of nitrogen (nitrogen-15) are important in studying the location of marine organisms such as fishes. The amount of sunlight trapped in marine organisms can be calculated from the ratio of these two stable nuclides.

Using stable isotopes, the diet and dietary pattern of the organism can be drawn. That is, you would be able to know whether the fish was a shallow feeder or a deep feeder. Conclusions as to whether it lived close to the shore or way inside the ocean can also be drawn using these isotopes. Ultimately, the food web in a specific water body can be drawn.


One important role of stable isotopes in medicine is as medical tracers. Patients’ responses to specific drugs could also be traced using stable isotopes. Common tracers used are isotopes of carbon, hydrogen, and nitrogen.

Stable nuclides of nitrogen-15 and carbon-13 are often used in pharmacology. They are used in identifying the active substance in drugs and for understanding the bio-availability of the drugs.

Ecological studies

Stable isotopes are used as ecological tools in deciphering the sources of materials introduced into the ecosystem. This implies that contaminants can be identified and their sources recognized. An insight into the behavior of organisms within a habitat can be understood using the stable isotopes found within a habitat.

Uses of Unstable Isotopes

Unstable nuclides have found uses in several areas. This is due to their radioactive nature. They undergo a change in form which releases energy. This energy can be tracked to measure or make specific discoveries.

Carbon dating

Every organic material is composed of a certain percentage of carbon. This can be absorbed from the atmosphere or ingested through food. This also includes the radioactive isotope, carbon-14. When the organism dies, they stop absorbing more carbon and the carbon-14 begins to decay.

It takes about 5,730 years for carbon-14 to decay to half its original amount. Thus, whatever is left after the first 5,730 years would be reduced to half its number again after another 5,730 years. Because carbon-14 is unstable, it decomposes to a more stable nitrogen-14. This method serves as a clock to measure the age of organic materials.

Using this, the estimated time the organism died could be determined making it an important tool in archaeology and geology.

As tracers

Radioisotopes of phosphorus are used to trace the uptake of phosphorus in plants. This serves as a tool in improving better fertilizer applications.

Adding small amounts of materials containing radioactive isotopes, it is possible to observe how some fluids flow. With this, it is easy to detect when there is a leakage.

Gamma radiations from radioisotopes are used to detect the reliability of metals. The metals are subjected to radiation from a source. Through this, faults in metals and the thickness of metals can be noted.


Radioisotopes of cesium-137 and cobalt-60 are used as preservatives for farm produce such as tomatoes, eggs, and fruits. These radiations destroy the bacteria that could cause the farm produce to spoil. The shelf life of the produces is extended and is safe for consumption.

Some radioactive particles are also employed to induce mutation to provide improved crop varieties. They are also used to hasten ripening processes.


Wines are made from vines. The fruit from these vines is gathered and pressed to produce different wines. Over the last hundred years, wines have been processed and stored. Many wine experts acclaim the quality of wine to its maturity based on how long ago it has been made. To impress people and make more sales, some recent wines are sold with labels bearing false dates of production.

In 1986, cesium-137 was accidentally introduced into the atmosphere. Some of the cesium was taken up by several plants. By calculating the amount of cesium present in wines, the vintages could be determined. This way, it is easy to identify the real-time production of wines.

Medical applications of radioisotopes

  • In diagnosis:

Some isotopes are used in the diagnosis of some conditions. An example is, iodine-131 which is used to check for thyroid activities. A calculated amount of iodine-131 is given to the patient and a scanner is used to measure the amount that collects at the thyroid gland. The thyroid gland is found in the neck and is a site for iodine concentration.

Other isotopes used in medical diagnosis include those of iron. These iron nuclides are used to diagnose anemic conditions in patients. Technetium-99m is also used in detecting liver conditions.

  • Treatments:

For treatments, a calculated amount of radioisotopes is administered to the patient. Specific nuclides can be used to treat specific conditions. Administering these isotopes in excess levels can become toxic and adversely affect the patient.

  • Medical Tracers:

Radioactive iodine is used in tracing the concentration of iodine in the thyroid gland.

Table showing some examples of isotopes and their uses

Industrial use
Medical use
Agricultural uses

(half-life: 432years)

·  In the determination of the thickness of paper and rolled steel

·  Used in locating oil wells


(half-life: 2.6years)

· In the determination of soil moisture content for road constructions

(half-life: 20 minutes)

· For PET scan in combination with glucose

(half-life: 5,730years)

·  To observe and study changes in patients with anemia, diabetes, and gout.
· Dating of organisms and materials

· For identifying the processes involved in photosynthesis



(half-life: 30.17years)

· In irradiation of farm produce

(half-life: 5.27years)

·  As radiation therapy for cancer prevention
·For irradiation of farm produce



(half-life: 8 days)

·   Used to monitor thyroid, cardiac, and liver activities.

· In the treatment of Graves’ disease

For locating tumors in the brain


(half-life; 72.8 days)

· To ascertain the reliability of parts of airplanes as well as of boilers
Phosphorus-32 and Phosphorus-33

(half-life: 14.8 days and 25.34 days respectively)

· Used in biology and genetics researches

(Half-life: 120 days)

· For studying proteins

(half-life: 14.9 hours)

· Used to identify leaks in pipes
  • Used in oil well studies.

(half-life: 4.8 days)

· To study metabolism and bone formation processes.



(half-life: 6hours)

·   Can be used to locate tumors in the brain

· In identifying damaged heart tissues and cells

· As a tracer in imaging of organs and to study blood flow.




(half-life: 73.1 hours)

·  Used to detect tumors and damages in the heart tissues
Tritium (hydrogen-3)

(half-life: 12.3 years)

· In identifying and measuring the age of groundwater up to 30 years.
· To observe and study the metabolism of drugs in organisms

(half-life: 703.8 million years)

·  As fuel in nuclear plants


·   Used to give absolute age in dating