Why are some nuclei stable while others decay?

Discover what makes a nucleus stable, why some atoms undergo radioactive decay, and how they move towards a more balanced state.

Not every nucleus is happy with its arrangement of particles or energy.

Some nuclei can exist unchanged indefinitely, while others are unstable and naturally transform into different nuclei. Unstable atoms “want” to become stable. They will release energy in the form of radiation, a process called radioactive decay. Atoms that will undergo radioactive decay are called radioactive atoms.

Each type of atom, let’s say Oxygen, for example, can have different versions that are either stable, or radioactive. Each specific version of radioactive Oxygen is called an isotope of Oxygen.

A nucleus is made of protons and neutrons. Protons have a positive electric charge, so they repel one another. On the other hand, the strong nuclear force helps hold protons and neutrons together.

For a nucleus to be stable, there needs to be a careful balance between these competing forces.

In smaller nuclei, stability usually comes from having a similar number of protons and neutrons. As nuclei get larger, they need extra neutrons to help hold the nucleus together without adding more positive charge and increasing proton repulsion.

(I like to think of neutrons as “spacers” that keep the “fighting” protons at a distance from each other, to help ease tensions. 😆)

If a nucleus has too many neutrons, too many protons, or simply too much energy, it may be unstable. It can then undergo radioactive decay to move towards a more stable arrangement.

There are several ways this can happen:

• Alpha decay

• Beta minus decay

• Beta plus decay

• Electron capture

• Gamma decay

• Internal conversion

(More on these in the next post.)

Every radioactive decay is a change towards a lower energy, more stable state. The nucleus does not choose when to decay, and we cannot predict the exact moment one individual nucleus will transform. However, the behavior of a large group of radioactive nuclei is highly predictable, which is why we can use radioactive materials safely and accurately in medicine.

Understanding nuclear stability helps us make sense of why radioactive isotopes exist, which type of radiation they emit, and how they can be used in imaging and treatment.

In the next post, we will explore the radioactive decay schemes in more detail.

Stay in tune with your isotopes,
Sara