Difference Between Isotope and Radioisotope

Main Difference – Isotope vs Radioisotope

Isotopes are different forms of the atoms of the same element. Radioisotopes are also a type of isotopes. But these isotopes are different since these are radioactive. This means these isotopes can undergo radioactive decay. Atoms undergo radioactive decay when their atoms are unstable. Therefore, the unstable isotopes of a particular chemical element are the radioisotopes of that element. The key difference between isotopes and radioisotopes is that isotopes may or may not undergo radioactive decay whereas radioisotopes essentially undergo radioactive decay.  

Key Areas Covered

1. What is an Isotope
      – Definition, Properties, Examples
2. What is a Radioisotope
      – Definition, Properties, Examples
3. What is the Difference Between Isotope and Radioisotope
      – Comparison of Key Differences

Key Terms: Half-life, Isotopes, Radioactive Decay, Radioactivity, Radioisotopes

Difference Between Isotope and Radioisotope - Comparison Summary

What is an Isotope

Isotopes are different forms of atoms of the same element. They are composed of the same number of protons in their nucleus and have the same atomic number. This is because atoms of the same element have the same atomic number. But the number of neutrons present in their nuclei are different from each other. Therefore, the atomic masses of isotopes are different from each other.

Some isotopes of certain chemical elements are stable where other isotopes are unstable. Stable isotopes can occur either alone or in combination with other elements in nature. But unstable isotopes cannot occur in nature. In order to become stable, these unstable isotopes undergo radioactive decay.

However, the chemical behavior of isotopes of a particular chemical element is the same because all the isotopes have the same number of electrons and the same atomic structure with respect to the electronic configuration. But they have different physical properties due to the differences in their atomic masses. These differences can be observed mainly in smaller chemical elements such as hydrogen.

Difference Between Isotope and Radioisotope

Figure 1: Isotopes of Hydrogen

For example, when the isotopes of hydrogen are considered, there are three main isotopes of hydrogen element. They are protium, deuterium, and tritium. All these isotopes have the same number of protons in their nucleus, one proton. Protium has no neutrons; deuterium has one neutron and tritium has two neutrons. Therefore, in hydrogen isotopes, the atomic masses have great differences between them. But, all these isotopes have only one electron. Therefore, the chemical properties of hydrogen isotopes are nearly the same.

What is a Radioisotope

A radioisotope is an unstable isotope of a chemical element that can undergo radioactive decay. Since these isotopes are unstable, they undergo radioactive decay in order to become stable. Most stable isotopes don’t show radioactivity.

The term “half-life” is defined as the time taken by a compound to get half of its initial mass through radioactive decay. For unstable radioisotopes, the half-life is very short. They quickly undergo radioactivity and become stable.

The radioactive decay causes emission of radiation. Unstable isotopes have a high number of neutrons or protons in their nuclei. Neutron-rich isotopes can emit radiation by converting neutrons into different particles. In proton-rich isotopes, protons are converted into different particles. These particles are emitted as radiation. There are three main types of radiation that a radioisotope can emit. They are alpha radiation, beta radiation, and gamma radiation. These radiations can harm our body by penetrating the skin. Therefore, we should take care when handling those elements.

Main Difference - Isotope vs Radioisotope

Figure 2: Radioisotopes are kept in safe boxes where the emitted radiation could not come out.

Radioisotopes are used in different applications due to their ability to emit radiation. For example, radioisotopes can be used to monitor processes such as DNA replication or amino acid transport. Heavy radioisotopes are used in nuclear power generation.

Difference Between Isotope and Radioisotope


Isotope: Isotopes are different forms of atoms of the same element.

Radioisotope: A radioisotope is an unstable isotope of a chemical element that can undergo radioactive decay.


Isotope: Isotopes can be either stable or unstable.

Radioisotope: Radioisotopes are unstable isotopes.


Isotope: Isotopes of some elements can show radioactivity.

Radioisotope: Radioisotopes essentially are radioactive.

Presence in Nature

Isotope: Stable isotopes can be found in the elemental form or in combination with other elements in nature.

Radioisotope: Radioisotopes can be found in nature for a short time period.


Isotope: Stable isotopes do not have half-lives but unstable isotopes have half-lives.

Radioisotope: Radioisotopes always have half-lives.


Radioisotopes are a type of isotopes. They are the unstable isotopes of a particular chemical element. Stable isotopes do not undergo radioactive decay because they can exist in nature as stable compounds. But radioisotopes are not stable. Therefore they have to undergo radioactive decay in order to become stable. This is the main difference between isotope and radioisotope.


1. Helmenstine, Anne Marie. “Know What Isotopes Are in Chemistry.” ThoughtCo, . Accessed 25 Sept. 2017.
2. “Radionuclide.” Wikipedia, Wikimedia Foundation, 22 Sept. 2017, . Accessed 25 Sept. 2017.
3. “What Are Isotopes? – Definition, Types & Examples.” Study.com, ,  Accessed 25 Sept. 2017.

Image Courtesy:

1. “The 3 isotopes of Hydrogen” By Johannes Schneider – Own work via
2. “Radioisotopes refrigerator” By real name: Nadina Wiórkiewiczpl.wiki: Nadine90commons: Nadine90 – Own work via

About the Author: Madhusha

Madhusha is a BSc (Hons) graduate in the field of Biological Sciences and is currently pursuing for her Masters in Industrial and Environmental Chemistry. Her interest areas for writing and research include Biochemistry and Environmental Chemistry.

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